Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

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  • 2020 • 256 On the reversible deactivation of cobalt ferrite spinel nanoparticles applied in selective 2-propanol oxidation
    Anke, S. and Falk, T. and Bendt, G. and Sinev, I. and Hävecker, M. and Antoni, H. and Zegkinoglou, I. and Jeon, H. and Knop-Gericke, A. and Schlögl, R. and Roldan Cuenya, B. and Schulz, S. and Muhler, M.
    Journal of Catalysis 382 57-68 (2020)
    CoFe2O4 nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N2 physisorption revealed non-porous spinel phase CoFe2O4 NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min−1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe2O4 yielding acetone and H2O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO2 was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O2 or N2O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O2 temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO2 during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies. © 2019 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2019.12.007
  • 2020 • 255 Enhanced dissolution of silver nanoparticles in a physical mixture with platinum nanoparticles based on the sacrificial anode effect
    Breisch, M. and Loza, K. and Pappert, K. and Rostek, A. and Rurainsky, C. and Tschulik, K. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
    Nanotechnology 31 (2020)
    A strategy to reduce implant-related infections is the inhibition of the initial bacterial implant colonization by biomaterials containing silver (Ag). The antimicrobial efficacy of such biomaterials can be increased by surface enhancement (nanosilver) or by creating a sacrificial anode system for Ag. Such a system will lead to an electrochemically driven enhanced Ag ion release due to the presence of a more noble metal. Here we combined the enlarged surface of nanoparticles (NP) with a possible sacrificial anode effect for Ag induced by the presence of the electrochemically more noble platinum (Pt) in physical mixtures of Ag NP and Pt NP dispersions. These Ag NP/Pt NP mixtures were compared to the same amounts of pure Ag NP in terms of cell biological responses, i.e. the antimicrobial activity against Staphylococcus aureus and Escherichia coli as well as the viability of human mesenchymal stem cells (hMSC). In addition, Ag NP was analyzed by ultraviolet-visible (UV-vis) spectroscopy, cyclic voltammetry, and atomic absorption spectroscopy. It was found that the dissolution rate of Ag NP was enhanced in the presence of Pt NP within the physical mixture compared to a dispersion of pure Ag NP. Dissolution experiments revealed a fourfold increased Ag ion release from physical mixtures due to enhanced electrochemical activity, which resulted in a significantly increased toxicity towards both bacteria and hMSC. Thus, our results provide evidence for an underlying sacrificial anode mechanism induced by the presence of Pt NP within physical mixtures with Ag NP. Such physical mixtures have a high potential for various applications, for example as antimicrobial implant coatings in the biomedicine or as bactericidal systems for water and surface purification in the technical area. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab4e48
  • 2020 • 254 Conductive films prepared from inks based on copper nanoparticles synthesized by transferred arc discharge
    Fu, Q. and Stein, M. and Li, W. and Zheng, J. and Kruis, F.E.
    Nanotechnology 31 (2020)
    Copper nanoparticles (NPs) are considered as a promising alternative for silver and gold NPs in conductive inks for the application of printing electronics, since copper shows a high electrical conductivity but is significantly cheaper than silver and gold. In this study, copper NPs were synthesized in the gas phase by transferred arc discharge, which has demonstrated scale-up potential. Depending on the production parameters, copper NPs can be continuously synthesized at a production rate of 1.2-5.5 g h-1, while their Brunauer-Emmett-Teller sizes were maintained below 100 nm. To investigate the suitability in electronic printing, we use ball milling technique to produce copper conductive inks. The effect of ball milling parameters on ink stability was discussed. In addition, the electrical resistivity of copper films sintered at 300 °C in reducing atmosphere was measured to be 5.4 ± 0.6 μΩ cm which is about three times higher than that of bulk copper (1.7 μΩ cm). This indicates that conductive inks prepared from gas-phase synthesized copper NPs are competitive to the conductive inks prepared from chemically synthesized copper NPs. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab4524
  • 2020 • 253 Diffusion of Gold Nanoparticles in Inverse Opals Probed by Heterodyne Dynamic Light Scattering
    Giraudet, C. and Knoll, M.S.G. and Galvan, Y. and Süß, S. and Segets, D. and Vogel, N. and Rausch, M.H. and Fröba, A.P.
    Transport in Porous Media 131 723-737 (2020)
    The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data. © 2019, Springer Nature B.V.
    view abstractdoi: 10.1007/s11242-019-01364-1
  • 2020 • 252 Gas-phase synthesis of iron oxide nanoparticles for improved magnetic hyperthermia performance
    Hammad, M. and Hardt, S. and Mues, B. and Salamon, S. and Landers, J. and Slabu, I. and Wende, H. and Schulz, C. and Wiggers, H.
    Journal of Alloys and Compounds 824 (2020)
    Magnetic nanoparticle-mediated hyperthermia has shown great potential in cancer therapy. However, upscaling of the synthesis of iron oxide nanoparticle with the required narrow size distribution remains challenging. This paper describes the reproducible and scalable synthesis of citric acid-functionalized iron oxide nanoparticles optimized for hyperthermia treatment. Iron oxide nanoparticles were synthesized by a spray flame method, which is eco-friendly and cost-effective. To the best of our knowledge, this is the first study reporting spray-flame synthesis of small iron oxide nanoparticles (approx. 7 nm) with narrow size distribution (polydispersity index ≪ 0.1). The citric acid-coated iron oxide nanoparticles revealed a hydrodynamic size of approx. 37 nm and a high magnetic saturation of 69 Am2/kg at room temperature. The magnetic hyperthermia study showed a significantly enhanced value of the intrinsic loss power (4.8 nHm2/kg), which is 1.5-fold higher than the best commercially available equivalents. The improved heating efficiency and small hydrodynamic size of citric acid-coated iron oxide nanoparticles demonstrate that the system could potentially be used as a nanoplatform for hyperthermia treatment. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.jallcom.2020.153814
  • 2020 • 251 Rational design of thiolated polyenes as trifunctional Raman reporter molecules in surface-enhanced Raman scattering nanotags for cytokine detection in a lateral flow assay
    Keller, T. and Brem, S. and Tran, V. and Sritharan, O. and Schäfer, D. and Schlücker, S.
    Journal of Biophotonics 13 (2020)
    The characteristic vibrational spectroscopic fingerprint of Raman reporter molecules adsorbed on noble metal nanoparticles is employed for the identification of target proteins by the corresponding surface-enhanced Raman scattering (SERS) nanotag-labeled antibodies. Here, we present the modular synthesis of thiolated polyenes with two to five C═C double bonds introduced via stepwise Wittig reactions. The experimental characterization of their electronic and vibrational properties is complemented by density functional theory calculations. Highly SERS-active nanotags are generated by using the thiolated polyenes as Raman reporter molecules in Au/Au core/satellite supraparticles with multiple hot spots. The cytokines IL-1β and IFN-γ are detected in a duplex SERS-based lateral flow assay on a nitrocellulose test strip by Raman microscopy. The thiolated polyenes are suitable for use in immuno-SERS applications such as point-of-care testing as well as cellular and tissue imaging. © 2020 The Authors. Journal of Biophotonics published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/jbio.201960126
  • 2020 • 250 Picosecond laser-induced surface structures on alloys in liquids and their influence on nanoparticle productivity during laser ablation
    Nadarajah, R. and Barcikowski, S. and Gökce, B.
    Optics Express 28 2909-2924 (2020)
    The productivity of nanoparticles formed by laser ablation of gold-silver and iron-gold alloy as well as copper and iron-nickel alloy targets in water is correlated with the formation of laser-induced surface structures. At a laser fluence optimized for maximum nanoparticle productivity, it is found that a binary alloy with an equimolar ratio forms laser-induced periodic surface structures (LIPSS) after ablation, if one of the constituent metals also form LIPSS. The ablation rate of nanoparticles linearly depends on the laser fluence if LIPSS is not formed, while a logarithmic trend and a decrease in productivity is evident when LIPSS is formed. To cancel LIPSS formation and recover from this decrease, a change to circularly polarized light is performed and an increase in nanoparticle productivity of more than 30% is observed. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
    view abstractdoi: 10.1364/OE.28.002909
  • 2020 • 249 Synthesis of plasmonic Fe/Al nanoparticles in ionic liquids
    Schmitz, A. and Meyer, H. and Meischein, M. and Garzón Manjón, A. and Schmolke, L. and Giesen, B. and Schlüsener, C. and Simon, P. and Grin, Y. and Fischer, R.A. and Scheu, C. and Ludwig, Al. and Janiak, C.
    RSC Advances 10 12891-12899 (2020)
    Bottom-up and top-down approaches are described for the challenging synthesis of Fe/Al nanoparticles (NPs) in ionic liquids (ILs) under mild conditions. The crystalline phase and morphology of the metal nanoparticles synthesized in three different ionic liquids were identified by powder X-ray diffractometry (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and fast Fourier transform (FFT) of high-resolution TEM images. Characterization was completed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) for the analysis of the element composition of the whole sample consisting of the NPs and the amorphous background. The bottom-up approaches resulted in crystalline FeAl NPs on an amorphous background. The top-down approach revealed small NPs and could be identified as Fe4Al13 NPs which in the IL [OPy][NTf2] yield two absorption bands in the green-blue to green spectral region at 475 and 520 nm which give rise to a complementary red color, akin to appropriate Au NPs. © 2020 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/d0ra01111h
  • 2020 • 248 Nanocellulose-Mediated Transition of Lithium-Rich Pseudo-Quaternary Metal Oxide Nanoparticles into Lithium Nickel Cobalt Manganese Oxide (NCM) Nanostructures
    Zehetmaier, P.M. and Zoller, F. and Beetz, M. and Plaß, M.A. and Häringer, S. and Böller, B. and Döblinger, M. and Bein, T. and Fattakhova-Rohlfing, D.
    ChemNanoMat 6 618-628 (2020)
    We report the syntheses of various compounds within the pseudo-quaternary system of the type LiwNixCoyMnzOδ (δ≤1) (pre-NCMs). Four different compositions of this compound were realized as ultrasmall crystalline nanoparticles of 1–4 nm diameter using low-temperature solvothermal reaction conditions in tert-butanol at only 170 °C. All of the pre-NCMs crystallize in the rock-salt structure and their lithium content is between 20% and 30% with respect to the complete metal content. By adjusting the lithium content to 105% stoichiometry in the solvothermal reaction, the pre-NCMs can easily react to the respective Li(NixCoyMnz)O2 (NCM) nanoparticles. Furthermore, nanosized desert-rose structured NCMs were obtained after addition of nanocellulose during the synthesis. By using the mixed metal monoxides as precursor for the NCMs, cation mixing between lithium and nickel is favored and gets more pronounced with increasing nickel content. The cation mixing effect compromises good electrochemical capacity retention, but the desert-rose structure nevertheless enables enhanced stability at high power conditions, especially for NCM333. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cnma.201900748
  • 2019 • 247 Electrical conductivity of silver nanoparticle doped carbon nanofibres measured by CS-AFM
    Ali, W. and Shabani, V. and Linke, M. and Sayin, S. and Gebert, B. and Altinpinar, S. and Hildebrandt, M. and Gutmann, J.S. and Mayer-Gall, T.
    RSC Advances 9 4553-4562 (2019)
    In this work, a pioneering study on the electrical properties of composite carbon nanofibres (CNFs) using current-sensitive atomic force microscopy (CS-AFM) has been demonstrated. CNFs are highly interesting materials which are usable in a wide array of applications e.g. electrode materials for biosensors, lithium ion batteries, fuel cells and supercapacitors. CNFs offer a high specific surface area and thus have a high contact area for charge transfer. CNFs can be produced using spinnable polyacrylonitrile (PAN) as a precursor for carbonisation. For the purpose of developing efficient CNFs with high conductivity and power density, silver nanoparticle (AgNPs)-containing PAN solutions were electrospun to form composite nanofibres which was followed by heat treatment. The applied voltage of the spinning setup and the content of both PAN and the silver nanoparticles in the spinning solution were varied in order to study their influence on the morphology and the electrical properties of the nanofibres. The resultant morphologies and fibre diameters were determined by scanning electron microscopy (SEM). The formation of silver nanoparticles was characterised in solution by UV-visible absorption spectroscopy and dynamic light scattering (DLS), while energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM) were carried out to investigate the presence as well as the average diameter of the AgNPs. The electrical properties of the CNFs were investigated using CS-AFM. This technique gives us the possibility to explore the electrical properties of single fibers and hence derive relationships between the structural features and the electrical properties. Our results show that the composite CNFs have a higher electrical conductivity than the neat CNFs and both the average diameter of the fibers and the electrical conductivity increase with an increasing AgNP content. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/C8RA04594A
  • 2019 • 246 Cobalt metalloid and polybenzoxazine derived composites for bifunctional oxygen electrocatalysis
    Barwe, S. and Andronescu, C. and Engels, R. and Conzuelo, F. and Seisel, S. and Wilde, P. and Chen, Y.-T. and Masa, J. and Schuhmann, W.
    Electrochimica Acta 297 1042-1051 (2019)
    The development of bifunctional oxygen electrodes is a key factor for the envisaged application of rechargeable metal-air batteries. In this work, we present a simple procedure based on pyrolysis of polybenzoxazine/metal metalloid nanoparticles composites into efficient bifunctional oxygen reduction and oxygen evolution electrocatalysts. This procedure generates nitrogen-doped carbon with embedded metal metalloid nanoparticles exhibiting high activity towards both, oxygen reduction and oxygen evolution, in 0.1 M KOH with a roundtrip voltage of as low as 0.81 V. Koutecký-Levich analysis coupled with scanning electrochemical microscopy reveals that oxygen is preferentially reduced in a 4e− transfer pathway to hydroxide rather than to hydrogen peroxide. Furthermore, the polybenzoxazine derived carbon matrix allows for stable catalyst fixation on the electrode surface, resulting in unattenuated activity during continuous alternate polarisation between oxygen evolution at 10 mA cm−2 and oxygen reduction at −1.0 mA cm−2. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2018.12.047
  • 2019 • 245 Bimetallic silver-platinum nanoparticles with combined osteo-promotive and antimicrobial activity
    Breisch, M. and Grasmik, V. and Loza, K. and Pappert, K. and Rostek, A. and Ziegler, N. and Ludwig, Al. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
    Nanotechnology 30 (2019)
    Bimetallic alloyed silver-platinum nanoparticles (AgPt NP) with different metal composition from Ag10Pt90 to Ag90Pt10 in steps of 20 mol% were synthesized. The biological effects of AgPt NP, including cellular uptake, cell viability, osteogenic differentiation and osteoclastogenesis as well as the antimicrobial activity towards Staphylococcus aureus and Escherichia coli were analyzed in comparison to pure Ag NP and pure Pt NP. The uptake of NP into human mesenchymal stem cells was confirmed by cross-sectional focused-ion beam preparation and observation by scanning and transmission electron microscopy in combination with energy-dispersive x-ray analysis. Lower cytotoxicity and antimicrobial activity were observed for AgPt NP compared to pure Ag NP. Thus, an enhanced Ag ion release due to a possible sacrificial anode effect was not achieved. Nevertheless, a Ag content of at least 50 mol% was sufficient to induce bactericidal effects against both Staphylococcus aureus and Escherichia coli. In addition, a Pt-related (≥50 mol% Pt) osteo-promotive activity on human mesenchymal stem cells was observed by enhanced cell calcification and alkaline phosphatase activity. In contrast, the osteoclastogenesis of rat primary precursor osteoclasts was inhibited. In summary, these results demonstrate a combinatory osteo-promotive and antimicrobial activity of bimetallic Ag50Pt50 NP. © 2019 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6528/ab172b
  • 2019 • 244 Effect of hepatic vein on gold nanoparticle-mediated-hyperthermia in liver cancer
    Jalali, M. and Mertin, P. and Rennings, A. and Erni, D.
    Proceedings of SPIE - The International Society for Optical Engineering 11207 (2019)
    Gold nanoparticle-mediated hyperthermia is a non-invasive, target-based cancer treatment with significantly reduced side effects compared to conventional treatments. In this work a simulation model for gold nanoparticlemediated hyperthermia is set up and used to investigate the case of a liver tumor located in the vicinity of a hepatic vein. Gold nanorods with optimized size and aspect ratio are embedded within the liver, and the temperature raise under CW laser illumination is calculated, while taking into account the convective heat transfer through blood perfusion. For this purpose, an analytical model based on the Navier-Stokes equation is used. Results show that due to the heat drain in the blood stream, an effective temperature raise is not achievable when the tumor is located in the vicinity of the hepatic vein. Additionally it is shown that even in the case of a 90% occluded vein, the temperature raise with such nanoparticle arrangement is still not enough for tumor ablation. © 2019 SPIE.
    view abstractdoi: 10.1117/12.2526978
  • 2019 • 243 Synthesis of Mixed AuZn Nanoparticles by Spark Discharge Technique
    Kala, S. and Kruis, F.E.
    MRS Advances 4 1621-1629 (2019)
    In this study, feasibility of spark discharge technique to generate mixed metal nanoparticles is demonstrated. Two immiscible metals Au and Zn are selected to prepare AuZn mixed nanoparticles. Ignition of spark between Au and Zn electrodes under normal pressure, in the presence of carrier gas, leads to formation of mixed nanoparticles by condensation and nucleation. Online particle size-distribution is monitored by a scanning mobility particle sizer on changing carrier gas flow rate and capacitor charging current during co-sparking between Au and Zn electrodes. The technique provides flexibility to generate binary mixture of AuZn nanoparticles in the size range of 10-80 nm. Distribution of Au and Zn in the prepared mixed nanoparticles is mapped by scanning electron microscopy and high resolution electron microscopy. © Materials Research Society 2019.
    view abstractdoi: 10.1557/adv.2019.221
  • 2019 • 242 Fe/Co/Ni mixed oxide nanoparticles supported on oxidized multi-walled carbon nanotubes as electrocatalysts for the oxygen reduction and the oxygen evolution reactions in alkaline media
    Kazakova, M.A. and Morales, D.M. and Andronescu, C. and Elumeeva, K. and Selyutin, A.G. and Ishchenko, A.V. and Golubtsov, G.V. and Dieckhöfer, S. and Schuhmann, W. and Masa, J.
    Catalysis Today (2019)
    Fabrication of efficient and cost-effective bifunctional oxygen electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remains a challenge for the development of rechargeable metal-air batteries and unitized regenerative fuel cells technologies. Herein, we report high-performance bifunctional ORR/OER electrocatalysts consisting of mixed transition metal (Fe, Co, Ni) oxide nanoparticles supported on oxidized multi-walled carbon nanotubes (MWCNT). Investigation of the ORR and OER activity of samples with different metal compositions showed that trimetallic/MWCNT composites having Fe:Ni:Co = x:x:(1-2x) ratios, with 0.25 ≤ x ≤ 0.4, exhibit highest bifunctional activity in terms of the reversible ORR/OER overvoltage at a given current density. Moreover, the trimetallic catalysts exhibited improved selectivity with respect to the reduction of O 2 to OH − compared to the bimetallic Fe-Ni, Fe-Co and Co-Ni catalysts, thus revealing synergistic interactions among the metal oxide components. Correlation of the electrocatalytic activity with the structure of the composites is discussed for the most representative cases. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.cattod.2019.02.047
  • 2019 • 241 Assessment of cytotoxicity and antibacterial effects of silver nanoparticle-doped titanium alloy surfaces
    Kirmanidou, Y. and Sidira, M. and Bakopoulou, A. and Tsouknidas, A. and Prymak, O. and Papi, R. and Choli-Papadopoulou, T. and Epple, M. and Michailidis, N. and Koidis, P. and Michalakis, K.
    Dental Materials 35 e220-e233 (2019)
    Objectives: This study aimed to develop silver nanoparticle (AgNP)-doped Ti6Al4V alloy surfaces and investigate their antibacterial properties against representative periopathogens and potential cytotoxicity on osteoblastic cells. Methods: AgNPs of different size distributions (5 and 30 nm) were incorporated onto the Ti6Al4V surfaces by electrochemical deposition, using colloid silver dispersions with increasing AgNP concentrations (100, 200 and 300 ppm). The time-course silver release from the specimen surfaces to cell culture media was assessed by Atomic Absorption Spectroscopy (AAS). Cell attachment, viability and proliferation were investigated by SEM, live/dead staining MTT and BrdU assays. The antibacterial effects were assessed against P. gingivalis and P. intermedia by serial dilution spotting assays. Results: A time- and concentration-dependent silver release from the experimental surfaces was observed. Overall, cell viability and attachment on the AgNP-doped surfaces, suggested adequate cytocompatibility at all concentrations. A transient cytotoxic effect was detected at 24 h for the 5 nm-sized groups that fully recovered at later time-points, while no cytotoxicity was observed for the 30 nm-sized groups. A statistically significant, concentration-dependent decrease in cell proliferation rates was induced at 48 h in all AgNP groups, followed by recovery at 72 h in the groups coated with 5 nm-sized AgNPs. A statistically significant, concentration-dependent antibacterial effect up to 30% was confirmed against both periopathogens. Significance: This study sheds light to the optimal size-related concentrations of AgNP-doped Ti6Al4V surfaces to achieve antibacterial effects, without subsequent cytotoxicity. These results significantly contribute to the development of antibacterial surfaces for application in oral implantology. © 2019 The Academy of Dental Materials
    view abstractdoi: 10.1016/
  • 2019 • 240 Epitaxial InGaAs Quantum Dots in Al0.29Ga0.71As Matrix: Intensity and Kinetics of Luminescence in the Near Field of Silver Nanoparticles
    Kosarev, A.N. and Chaldyshev, V.V. and Kondikov, A.A. and Vartanyan, T.A. and Toropov, N.A. and Gladskikh, I.A. and Gladskikh, P.V. and Akimov, I. and Bayer, M. and Preobrazhenskii, V.V. and Putyato, M.A. and Semyagin, B.R.
    Optics and Spectroscopy 126 492-496 (2019)
    Abstract: Quantum dots of indium gallium arsenide buried in a thin layer of aluminum gallium arsenide were grown by means of molecular-beam epitaxy. The influence of silver nanoparticles grown on the surface of the semiconductor structure by vacuum thermal evaporation on photoluminescence of quantum dots was investigated. Photoluminescence spectra of quantum dots were obtained under stationary and pulsed excitation. The influence of silver nanoparticles exhibiting plasmon resonances on spectral distribution and kinetics of luminescence of the epitaxial quantum dots was studied. © 2019, Pleiades Publishing, Ltd.
    view abstractdoi: 10.1134/S0030400X19050151
  • 2019 • 239 Impact of Preparation Method and Hydrothermal Aging on Particle Size Distribution of Pt/γ-Al2O3 and Its Performance in CO and NO Oxidation
    Ogel, E. and Casapu, M. and Doronkin, D.E. and Popescu, R. and Störmer, H. and Mechler, C. and Marzun, G. and Barcikowski, S. and Türk, M. and Grunwaldt, J.-D.
    Journal of Physical Chemistry C 123 5433-5446 (2019)
    The influence of the preparation method and the corresponding particle size distribution on the hydrothermal deactivation behavior at 600-800 °C and performance during CO/NO oxidation was systematically investigated for a series of Pt/Al2O3 catalysts. Representative conventional (incipient wetness impregnation) and advanced preparation methods (flame spray pyrolysis, supercritical fluid reactive deposition, and laser ablation in liquid) were selected, which generated samples containing narrow and homogeneous but also heterogeneous particle size distributions. Basic characterization was conducted by inductively coupled plasma-optical emission spectrometry, N2 physisorption, and X-ray diffraction. The particle size distribution and the corresponding oxidation state were analyzed using transmission electron microscopy and X-ray absorption spectroscopy. The systematic study shows that oxidized Pt nanoparticles smaller than 2 nm sinter very fast, already at 600 °C, but potential chlorine traces from the catalyst precursor seem to stabilize Pt nanoparticles against further sintering and consequently maintain the catalytic performance. Samples prepared by flame spray pyrolysis and laser ablation showed a superior hydrothermal resistance of the alumina support, although, due to small interparticle distance in case of laser synthesized particles, the particle size distribution increases considerably at high temperatures. Significant deceleration of the noble metal sintering process was obtained for the catalysts containing homogeneously distributed but slightly larger Pt nanoparticles (supercritical fluid reactive deposition) or for particles deposited on a thermally stable alumina support (flame spray pyrolysis). The correlations obtained between Pt particle size distribution, oxidation state, and catalytic performance indicate different trends for CO and NO oxidation reactions, in line with their structure sensitivity. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b11065
  • 2019 • 238 Impact of Preparation Method and Hydrothermal Aging on Particle Size Distribution of Pt/γ-Al 2 O 3 and Its Performance in CO and NO Oxidation
    Ogel, E. and Casapu, M. and Doronkin, D.E. and Popescu, R. and Störmer, H. and Mechler, C. and Marzun, G. and Barcikowski, S. and Türk, M. and Grunwaldt, J.-D.
    Journal of Physical Chemistry C (2019)
    The influence of the preparation method and the corresponding particle size distribution on the hydrothermal deactivation behavior at 600-800 °C and performance during CO/NO oxidation was systematically investigated for a series of Pt/Al 2 O 3 catalysts. Representative conventional (incipient wetness impregnation) and advanced preparation methods (flame spray pyrolysis, supercritical fluid reactive deposition, and laser ablation in liquid) were selected, which generated samples containing narrow and homogeneous but also heterogeneous particle size distributions. Basic characterization was conducted by inductively coupled plasma-optical emission spectrometry, N 2 physisorption, and X-ray diffraction. The particle size distribution and the corresponding oxidation state were analyzed using transmission electron microscopy and X-ray absorption spectroscopy. The systematic study shows that oxidized Pt nanoparticles smaller than 2 nm sinter very fast, already at 600 °C, but potential chlorine traces from the catalyst precursor seem to stabilize Pt nanoparticles against further sintering and consequently maintain the catalytic performance. Samples prepared by flame spray pyrolysis and laser ablation showed a superior hydrothermal resistance of the alumina support, although, due to small interparticle distance in case of laser synthesized particles, the particle size distribution increases considerably at high temperatures. Significant deceleration of the noble metal sintering process was obtained for the catalysts containing homogeneously distributed but slightly larger Pt nanoparticles (supercritical fluid reactive deposition) or for particles deposited on a thermally stable alumina support (flame spray pyrolysis). The correlations obtained between Pt particle size distribution, oxidation state, and catalytic performance indicate different trends for CO and NO oxidation reactions, in line with their structure sensitivity. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b11065
  • 2019 • 237 Early appearance of crystalline nanoparticles in pulsed laser ablation in liquids dynamics
    Reich, S. and Letzel, A. and Menzel, A. and Kretzschmar, N. and Gökce, B. and Barcikowski, S. and Plech, A.
    Nanoscale 11 6962-6969 (2019)
    The size and crystallinity of gold and silver nanoparticles during the process of pulsed laser ablation in water (PLAL) is investigated with microsecond and sub-microsecond time resolution. While basic observations have already been established, such as detection of particles inside the cavitation bubble, trapping of ablated matter by the bubble or the action of size quenching on a sub-millisecond time scale, the structure formation mechanism is still a matter of debate. Quantifying the nanoparticle release and crystallinity close to the irradiated metal target by wide and small angle X-ray scattering reveals the presence of nanoparticles ahead of the developing vapour bubble and inside the bubble. While the (temporal) distribution is in agreement with a homogeneously particle-filled bubble, solid particles are detected at the advancing bubble front. Wide-angle X-ray scattering confirms the crystalline nature of these large particles. This reveals that for picosecond ablation the expulsion of condensed phases of material during the ablation process adds significantly to the bimodal size distribution, relating to recent models of film lift-off and liquid metal Rayleigh instabilities. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9nr01203f
  • 2019 • 236 Design and optimization of a medium flow differential mobility analyzer (MF-DMA) for classification of high-density particles
    Rosenberger, T. and Kiesler, D. and Hontañón, E. and Fuentes, D. and Ramiro, E. and Kruis, F.E.
    Aerosol Science and Technology 53 1172-1185 (2019)
    A new design of a Differential Mobility Analyzer (DMA) was tested with medium aerosol flow rates ranging from 1.5 to 10 slm and high-density particles. The vacuum-tight construction makes it possible to classify pure metal nanoparticles from production processes. The selectable electrical mobility range is comparable to the TSI Long and Nano DMA and covers the full nanometer scale from 15–600 nm. The Medium Flow-DMA (MF-DMA) is characterized by its transfer function, which was determined by a tandem DMA setup using a SMPS with Long DMA downstream. Silver nanoparticles with a density of 10.49 g cm−3 were used to demonstrate the size-selecting performance of high-density particles. The transfer function was calculated for aerosol to sheath gas flow ratios of 1/10, 1/5, and 1/3 directly from the SMPS data by a new method using modeling approach and comparison to the theory. Sufficiently high resolution was reached by increasing the SMPS scan time of the classified size distribution to 300 s. During the investigation, a broadened transfer function could be attributed to an inhomogeneous flow field resulting from the aerosol inlet design. The aerosol inlet of the MF-DMA was optimized by the number of inlet drillings and the opening of the inlet slit to achieve a more homogeneous flow field. CFD simulations of the MF-DMA also confirmed this. The modification improved the transfer function especially for medium aerosol flow rates above 5 slm. Copyright © 2019 American Association for Aerosol Research. © 2019, © 2019 American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2019.1642443
  • 2019 • 235 X-ray powder diffraction to analyse bimetallic core-shell nanoparticles (gold and palladium; 7-8 nm)
    Rostek, A. and Loza, K. and Heggen, M. and Epple, M.
    RSC Advances 9 26628-26636 (2019)
    A comparative X-ray powder diffraction study on poly(N-vinyl pyrrolidone) (PVP)-stabilized palladium and gold nanoparticles and bimetallic Pd-Au nanoparticles (both types of core-shell nanostructures) was performed. The average diameter of Au and Pd nanoparticles was 5 to 6 nm. The two types of core-shell particles had a core diameter of 5 to 6 nm and an overall diameter of 7 to 8 nm, i.e. a shell thickness of 1 to 2 nm. X-ray powder diffraction on a laboratory instrument was able to distinguish between a physical mixture of gold and palladium nanoparticles and bimetallic core-shell nanoparticles. It was also possible to separate the core from the shell in both kinds of bimetallic core-shell nanoparticles due to the different domain size and because it was known which metal was in the core and which was in the shell. The spherical particles were synthesized by reduction with glucose in aqueous media. After purification by multiple centrifugation steps, the particles were characterized with respect to their structural, colloid-chemical, and spectroscopic properties, i.e. particle size, morphology, and internal elemental distribution. Dynamic light scattering (DLS), differential centrifugal sedimentation (DCS), atomic absorption spectroscopy (AAS), ultraviolet-visible spectroscopy (UV-vis), high-angle annular dark field imaging (HAADF), and energy-dispersed X-ray spectroscopy (EDX) were applied for particle characterization. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9ra05117a
  • 2019 • 234 Solution NMR Spectroscopy with Isotope-Labeled Cysteine (13C and 15N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 767-778 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13C-labeled and 15N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1H-13C-heteronuclear single-quantum coherence and 13C-13C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy (1H-, 13C-, and 1H-13C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au174(cysteine)67. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b03840
  • 2019 • 233 Solution NMR Spectroscopy with Isotope-Labeled Cysteine ( 13 C and 15 N) Reveals the Surface Structure of l -Cysteine-Coated Ultrasmall Gold Nanoparticles (1.8 nm)
    Ruks, T. and Beuck, C. and Schaller, T. and Niemeyer, F. and Zähres, M. and Loza, K. and Heggen, M. and Hagemann, U. and Mayer, C. and Bayer, P. and Epple, M.
    Langmuir 35 767-778 (2019)
    Ultrasmall gold nanoparticles with a diameter of 1.8 nm were synthesized by reduction of tetrachloroauric acid with sodium borohydride in the presence of l-cysteine, with natural isotope abundance as well as 13 C-labeled and 15 N-labeled. The particle diameter was determined by high-resolution transmission electron microscopy and differential centrifugal sedimentation. X-ray photoelectron spectroscopy confirmed the presence of metallic gold with only a few percent of oxidized Au(+I) species. The surface structure and the coordination environment of the cysteine ligands on the ultrasmall gold nanoparticles were studied by a variety of homo- and heteronuclear NMR spectroscopic techniques including 1 H- 13 C-heteronuclear single-quantum coherence and 13 C- 13 C-INADEQUATE. Further information on the binding situation (including the absence of residual or detached l-cysteine in the solution) and on the nanoparticle diameter (indicating the well-dispersed state) was obtained by diffusion-ordered spectroscopy ( 1 H-, 13 C-, and 1 H- 13 C-DOSY). Three coordination environments of l-cysteine on the gold surface were identified that were ascribed to different crystallographic sites, supported by geometric considerations of the nanoparticle ultrastructure. The particle size data and the NMR-spectroscopic analysis gave a particle composition of about Au 174 (cysteine) 67 . © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b03840
  • 2019 • 232 Aggregation control of Ru and Ir nanoparticles by tunable aryl alkyl imidazolium ionic liquids
    Schmolke, L. and Lerch, S. and Bülow, M. and Siebels, M. and Schmitz, A. and Thomas, J. and Dehm, G. and Held, C. and Strassner, T. and Janiak, C.
    Nanoscale 11 3773-3779 (2019)
    Metal-nanoparticles (M-NPs) were synthesized in a wet-chemical synthesis route in tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl-substituted imidazolium motif from Ru3(CO)12 and Ir4(CO)12 by microwave-heating induced thermal decomposition. The size and size dispersion of the NPs were determined by transmission electron microscopy (TEM) to an average diameter of 2.2(±0.1) to 3.9(±0.3) nm for Ru-NPs and to an average diameter of 1.4(±0.1) to 2.4(±0.1) nm for Ir-NPs. The TAAILs used contain the same bis(trifluoromethylsulfonyl)imide anion but differ in the substituents on the 1-aryl ring, e.g. 2-methyl-, 4-methoxy- and 2,4-dimethyl groups and in the 3-alkyl chain lengths (C4H9, C5H11, C8H17, C9H19, C11H23). All used TAAILs are suitable for the stabilization of Ru- and Ir-NPs over months in the IL dispersion. Different from all other investigations on M-NP/IL systems which we are aware of the particle separation properties of the TAAILs vary strongly as a function of the aryl substituent. Good NP separation can be achieved with the 4-methoxyphenyl- and 2,4-dimethylphenyl-substituted ILs, irrespective of the 3-alkyl chain lengths. Significant aggregation can be observed for 2-methylphenyl-substituted ILs. The good NP separation can be correlated with a negative electrostatic potential at the 4-methoxyphenyl or 4-methylphenyl substituent that is in the para-position of the aryl ring, whereas the 2-(ortho-)methylphenyl group assumes no negative potential. ϵ-ePC-SAFT calculations were used to validate that the interactions between ILs and the washing agents (required for TEM analyses) do not cause the observed aggregation/separation behaviour of the M-NPs. Ru-NPs were investigated as catalysts for the solvent-free hydrogenation of benzene to cyclohexane under mild conditions (70 °C, 10 bar) with activities up to 760 (mol cyclohexane) (mol Ru)-1 h-1 and over 95% conversion in ten consecutive runs for Ru-NPs. No significant loss of catalytic activity could be observed. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8nr10286d
  • 2019 • 231 Milling Down to Nanometers: A General Process for the Direct Dry Synthesis of Supported Metal Catalysts
    Schreyer, H. and Eckert, R. and Immohr, S. and de Bellis, J. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition 58 11262-11265 (2019)
    Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet-chemical methods, such as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO2, Al2O3, Fe2O3, and Co3O4, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost-effective alternative to the conventionally used impregnation methods. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201903545
  • 2019 • 230 Precision Plasmonics with Monomers and Dimers of Spherical Gold Nanoparticles: Nonequilibrium Dynamics at the Time and Space Limits
    Schumacher, L. and Jose, J. and Janoschka, D. and Dreher, P. and Davis, T.J. and Ligges, M. and Li, R. and Mo, M. and Park, S. and Shen, X. and Weathersby, S. and Yang, J. and Wang, X. and Meyer Zu Heringdorf, F. and Sokolowski-Ti...
    Journal of Physical Chemistry C 123 13181-13191 (2019)
    Monomers and dimers of spherical gold nanoparticles (NPs) exhibit highly uniform plasmonic properties at the single-particle level due to their high structural homogeneity (precision plasmonics). Recent investigations in precision plasmonics have largely focused on static properties using conventional techniques such as transmission electron microscopy and optical dark-field microscopy. In this Feature Article, we first highlight the application of femtosecond time-resolved electron diffraction for monitoring the nonequilibrium dynamics of spherical gold NPs after ultrafast optical excitation. The analysis of the transient diffraction patterns allows us to directly obtain quantitative information on the incoherent excitation of the lattice, that is, heating upon electron-lattice equilibration, as well as on the development of strain due to lattice expansion on picosecond time scales. The controlled assembly of two spherical gold NPs into a dimer with a few nanometers gap leads to unique optical properties. Specifically, extremely high electric fields (hot spot) in the gap are generated upon resonant optical excitation. Conventional optical microscopy cannot spatially resolve this unique hot spot due to the optical diffraction limit. We therefore employed nonlinear photoemission electron microscopy to visualize hot spots in single dimers of spherical gold NPs. A quantitative comparison of different single dimers confirms the homogeneity of the hot spots on the single-particle level. Overall, these initial results are highly encouraging because they pave the way to investigate nonequilibrium dynamics in highly uniform plasmonic nanostructures at the time and space limits. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.9b01007
  • 2019 • 229 Detailed simulation of iron oxide nanoparticle forming flames: Buoyancy and probe effects
    Sellmann, J. and Rahinov, I. and Kluge, S. and Jünger, H. and Fomin, A. and Cheskis, S. and Schulz, C. and Wiggers, H. and Kempf, A. and Wlokas, I.
    Proceedings of the Combustion Institute 37 1241-1248 (2019)
    Nanoparticle formation in flames is strongly influenced by the residence-time-temperature history inside the flame. We study how the temperature history can be intentionally modified by orienting flames either in an upward-firing or downward-firing configuration. We also investigate the influence of unintended residence-time modifications caused by sampling nozzles. These phenomena are investigated by experiments and simulations for the synthesis of iron oxide nanoparticles from premixed iron-pentacarbonyl-doped hydrogen/oxygen flat flames. The experiments apply molecular-beam sampling with a particle mass spectrometer to measure particle sizes and a quartz microbalance to detect the presence of condensed matter. The simulations rely on a finite-rate chemistry approach with species-specific diffusion, particle dynamics are described by a bi-modal population balance model. It is demonstrated that the downward-burning flame forms a detached stagnation point, causing longer residence times at elevated temperature than an upward- or horizontally firing flame, permitting the growth of larger particles. These iron oxide particles are eventually formed in the recombination zone of the flame, but no condensed matter was found in the reaction zone. The experiments also observed the formation of particles in the preheat zone, but their composition and all aspects of their disappearance remain uncertain. Current models do, however, suggest the formation of iron particles and their subsequent evaporation and combustion. © 2018 The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2018.06.041
  • 2019 • 228 Photocatalytic one-step synthesis of Ag nanoparticles without reducing agent and their catalytic redox performance supported on carbon
    Shui, L. and Zhang, G. and Hu, B. and Chen, X. and Jin, M. and Zhou, G. and Li, N. and Muhler, M. and Peng, B.
    Journal of Energy Chemistry 36 37-46 (2019)
    Synthesis of silver nanoparticles (Ag NPs) with state-of-the-art chemical or photo-reduction methods generally takes several steps and requires both reducing agents and stabilizers to obtain NPs with narrow size distribution. Herein, we report a novel method to synthesize Ag NPs rapidly in one step, achieving typical particle sizes in the range from 5 to 15 nm. The synthesis steps only involve three chemicals without any reducing agent: AgNO3 as precursor, polyvinylpyrrolidone (PVP) as stabilizer, and AgCl as photocatalyst. The Ag NPs were supported on carbon and showed excellent performance in thermal catalytic p-nitrophenol reduction and nitrobenzene hydrogenation, and as electrocatalyst for the oxygen reduction reaction. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences
    view abstractdoi: 10.1016/j.jechem.2019.04.006
  • 2019 • 227 Biomimetic fabrication of mineralized composite films of nanosilver loaded native fibrillar collagen and chitosan
    Socrates, R. and Prymak, O. and Loza, K. and Sakthivel, N. and Rajaram, A. and Epple, M. and Narayana Kalkura, S.
    Materials Science and Engineering C 99 357-366 (2019)
    Silver nanoparticles loaded fibrillar collagen-chitosan matrix (CC) was prepared by biomimetic approach by blending silver nanoparticles (tAgNPs), collagen fibril and chitosan hydrogel followed by cross-linking and biomineralization. Electron micrograph showed that the surface of the composites exhibited native fibrillar morphology of collagen and their cross-section revealed layer-like arrangement of native fibrillar collagen. The mineralized composites exhibited surface mineralization of calcium phosphates incorporated with magnesium. FT-IR ATR analysis revealed the uniform blending of collagen and chitosan without any chemical interaction between them. XRD analysis showed incorporation of silver nanoparticles and lamellar structure of collagen and chitosan. The mechanical property of the dry composite film showed increase in tensile strength with the addition of chitosan and raised to 4.6 fold in M-CC4 composite. The incorporation of chitosan in M-CC3 led to 2.2 fold increase in mineralization as confirmed by the TGA analysis. Contact angle analysis revealed the hydrophilic nature of the composite. Hemolysis analysis of the composites verified the hemocompatible nature of composites with hemolysis < 5%. MTT assay for the composites was carried by seeding MG-63 cells and indicated cell viability > 80%. Antibacterial activity analysis showed the percent growth inhibition of about 27% and 37% for S. aureus and E. coli respectively. The prepared composite would possess silver nanoparticles loaded collagen fibril in the native state and the formed biomineral will be similar to the bone mineral. Hence the fabricated composite -could be used as a biomaterial for bone tissue engineering applications. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2019.01.101
  • 2019 • 226 Scanning Electrochemical Cell Microscopy Investigation of Single ZIF-Derived Nanocomposite Particles as Electrocatalysts for Oxygen Evolution in Alkaline Media
    Tarnev, T. and Aiyappa, H.B. and Botz, A. and Erichsen, T. and Ernst, A. and Andronescu, C. and Schuhmann, W.
    Angewandte Chemie - International Edition 58 14265-14269 (2019)
    “Single entity” measurements are central for an improved understanding of the function of nanoparticle-based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF-67)-derived Co−N-doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non-interfering Os complex as free-diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s−1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/anie.201908021
  • 2019 • 225 Click Chemistry on the Surface of Ultrasmall Gold Nanoparticles (2 nm) for Covalent Ligand Attachment Followed by NMR Spectroscopy
    Van Der Meer, S.B. and Loza, K. and Wey, K. and Heggen, M. and Beuck, C. and Bayer, P. and Epple, M.
    Langmuir 35 7191-7204 (2019)
    Ultrasmall gold nanoparticles (core diameter 2 nm) were surface-conjugated with azide groups by attaching the azide-functionalized tripeptide lysine(N3)-cysteine-asparagine with ∼117 molecules on each nanoparticle. A covalent surface modification with alkyne-containing molecules was then possible by copper-catalyzed click chemistry. The successful clicking to the nanoparticle surface was demonstrated with 13C-labeled propargyl alcohol. All steps of the nanoparticle surface conjugation were verified by extensive NMR spectroscopy on dispersed nanoparticles. The particle diameter and the dispersion state were assessed by high-resolution transmission electron microscopy (HRTEM), differential centrifugal sedimentation (DCS), and 1H-DOSY NMR spectroscopy. The clicking of fluorescein (FAM-alkyne) gave strongly fluorescing ultrasmall nanoparticles that were traced inside eukaryotic cells. The uptake of these nanoparticles after 24 h by HeLa cells was very efficient and showed that the nanoparticles even penetrated the nuclear membrane to a very high degree (in contrast to dissolved FAM-alkyne alone that did not enter the cell). About 8 fluorescein molecules were clicked to each nanoparticle. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.9b00295
  • 2019 • 224 Kinetically-controlled laser-synthesis of colloidal high-entropy alloy nanoparticles
    Waag, F. and Li, Y. and Ziefuß, A.R. and Bertin, E. and Kamp, M. and Duppel, V. and Marzun, G. and Kienle, L. and Barcikowski, S. and Gökce, B.
    RSC Advances 9 18547-18558 (2019)
    The single-step incorporation of multiple immiscible elements into colloidal high-entropy alloy (HEA) nanoparticles has manifold technological potential, but it continues to be a challenge for state-of-the-art synthesis methods. Hence, the development of a synthesis approach by which the chemical composition and phase of colloidal HEA nanoparticles can be controlled could lead to a new pool of nanoalloys with unparalleled functionalities. Herein, this study reports the single-step synthesis of colloidal CoCrFeMnNi HEA nanoparticles with targeted equimolar stoichiometry and diameters less than 5 nm by liquid-phase, ultrashort-pulsed laser ablation of the consolidated and heat-treated micropowders of the five constituent metals. Further, the scalability of the process with an unprecedented productivity of 3 grams of colloidal HEA nanoparticles per hour is demonstrated. Electrochemical analysis reveals a unique redox behavior of the particles' surfaces in an alkaline environment and a potential for future application as a heterogeneous catalyst for the oxygen evolution reaction. © 2019 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c9ra03254a
  • 2019 • 223 The electrochemical dissolution of single silver nanoparticles enlightened by hyperspectral dark-field microscopy
    Wonner, K. and Evers, M.V. and Tschulik, K.
    Electrochimica Acta 301 458-464 (2019)
    Nowadays, silver nanoparticles are extensively employed in several branches of industry and medicine. Hence, those particles are amongst the most studied class of nanomaterials, yet their reactivity and in particular their reactivity in biological systems is still poorly understood. This discrepancy leads to a huge demand for further insights into the reaction dynamics of electrochemical reactions. For this purpose, coupled opto- and spectro-electrochemical dark-field microscopy is used herein to study the electrochemical oxidation and dissolution process of individual silver nanoparticles in thiocyanate solutions. It is observed, that upon electrochemical oxidation of silver, a silver thiocyanate complex is formed. This is indicated by a change of both the measured plasmon resonance frequency and scattering intensity, simultaneous to the detection of an oxidative current. Subsequently, this silver pseudo-halide is chemically converted to a silver thiocyanate complex with higher solubility in the presence of high thiocyanate concentrations. This follow-up reaction is only detectable thanks to in situ spectroscopy as no current is associated with this chemical conversion but a distinct change in the spectroscopy response of the individual particles is seen. We were thus able to reveal that the total conversion of silver nanoparticles in the presence of thiocyanate is a multi-step process which lasts much longer than the electrochemical response suggests. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2019.01.129
  • 2019 • 222 Sensitive and selective detection of Cu2+ ions based on fluorescent Ag nanoparticles synthesized by R-phycoerythrin from marine algae Porphyra yezoensis
    Xu, Y. and Hou, Y. and Wang, Y. and Wang, Y. and Li, T. and Song, C. and Wei, N. and Wang, Q.
    Ecotoxicology and Environmental Safety 168 356-362 (2019)
    In this study, using a natural and green protein R-phycoerythrin (R-PE) extracted from marine Porphyra yezoensis as the stabilizer and reducer, silver nanoparticles (AgNPs) were synthesized. Based on this, a highly sensitive and selective method for the detection of Cu2+ ions was developed using R-PE-AgNPs as fluorescent probe. The interactions between R-PE-AgNPs and Cu2+ ions were systematically characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), elemental mapping and Fourier transform infrared (FTIR). It was found that Cu2+ ions could cause aggregation of the R-PE-AgNPs, accompanied by the greatly increased particle size. Importantly, the method offered a wide linear detection range from 0 μM to 100.0 μM with a detection limit of 0.0190 μM. Moreover, the proposed method was successfully applied to analyze Cu2+ ions in tap water and lake water samples, acquiring satisfactory recovery between 91.6% and 102.2%. Such a green, fast and cost-effective fluorimetric method of the R-PE-AgNPs probe has great potential for tracing Cu2+ ions in diverse aqueous media. © 2018 Elsevier Inc.
    view abstractdoi: 10.1016/j.ecoenv.2018.10.102
  • 2019 • 221 Surface Plasmon Coupling in Dimers of Gold Nanoparticles: Experiment and Theory for Ideal (Spherical) and Nonideal (Faceted) Building Blocks
    Yoon, J.H. and Selbach, F. and Schumacher, L. and Jose, J. and Schlücker, S.
    ACS Photonics 6 642-648 (2019)
    The surface plasmon (SP) coupling in dimers of spherical and faceted gold nanoparticles was investigated experimentally and computationally at the single-particle level. Individual ideal dimers of two spherical gold nanoparticles with a constant gap, filled by a self-assembled monolayer of 1,8-octanedithiol linker molecules, exhibit highly uniform dark-field (DF) scattering spectra. In contrast, single nonideal dimers of two faceted gold nanoparticles with the same constant gap exhibit a high degree of spectral nonuniformity. We attribute this significant spectral heterogeneity to the many possible gap morphologies, that is, the many possible configurations of the crystal facet orientations at the junction of the two faceted particles in nonideal dimers. This configurational complexity is reduced in so-called hybrid dimers, which comprise an ideal spherical particle and a nonideal faceted particle. Hybrid dimers were therefore investigated theoretically and experimentally for revealing the influence of crystal facet orientation in the gap. Computed scattering spectra of ideal dimers (two spheres) and three different configurations of hybrid dimers (sphere and icosahedron) with face, edge, or point contact, respectively, were obtained using the finite-difference time-domain method. Theory predicts a blue shift of the longitudinal bonding dipolar plasmon coupling mode for hybrid dimers with point and edge contacts, but a red shift for face contact due to the stronger SP coupling. Experimental DF scattering spectra of individual hybrid dimers were measured for comparison with the predictions from theory. All single-particle DF scattering spectra of hybrid dimers exhibit either a blue shift (two distinct classes) or a red shift relative to the corresponding ideal dimers, in agreement with the predictions from computer simulations. Copyright © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acsphotonics.8b01424
  • 2018 • 220 Catalyst Support Effect on the Activity and Durability of Magnetic Nanoparticles: Toward Design of Advanced Electrocatalyst for Full Water Splitting
    Davodi, F. and Mühlhausen, E. and Tavakkoli, M. and Sainio, J. and Jiang, H. and Gökce, B. and Marzun, G. and Kallio, T.
    ACS Applied Materials and Interfaces 10 31300-31311 (2018)
    Earth-abundant element-based inorganic-organic hybrid materials are attractive alternatives for electrocatalyzing energy conversion reactions. Such material structures do not only increase the surface area and stability of metal nanoparticles (NPs) but also modify the electrocatalytic performance. Here, we introduce, for the first time, multiwall carbon nanotubes (MWNTs) functionalized with nitrogen-rich emeraldine salt (ES) (denoted as ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe2O3) NPs. The latter component has been synthesized by a simple and upscalable one-step pulsed laser ablation method on Ni core forming the core-shell Niγ-Fe2O3 NPs. The catalyst (Niγ-Fe2O3/ES-MWNT) is formed via self-assembly as strong interaction between ES-MWNT and Niγ-Fe2O3 results in NPs' encapsulation in a thin C-N shell. We further show that Ni does not directly function as an active site in the electrocatalyst but it has a crucial role in synthesizing the maghemite shell. The strong interaction between the NPs and the support improves notably the NPs' catalytic activity toward oxygen evolution reaction (OER) in terms of both onset potential and current density, ranking it among the most active catalysts reported so far. Furthermore, this material shows a superior durability to most of the current excellent OER electrocatalysts as the activity, and the structure, remains almost intact after 5000 OER stability cycles. On further characterization, the same trend has been observed for hydrogen evolution reaction, the other half-reaction of water splitting. Copyright © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acsami.8b08830
  • 2018 • 219 Role of Citrate and NaBr at the Surface of Colloidal Gold Nanoparticles during Functionalization
    Dinkel, R. and Jakobi, J. and Ziefuß, A.R. and Barcikowski, S. and Braunschweig, B. and Peukert, W.
    Journal of Physical Chemistry C 122 27383-27391 (2018)
    A molecular understanding of the ligand shell and the functionalization process is essential for the development of surface-functionalized gold nanoparticles (AuNPs). Obviously, the initial ligand shell from the synthesis plays a crucial role in this process. Here, in situ second-harmonic scattering is applied to study the adsorption of a 3-mercapto-1-propanesulfonate (MPS) at the surface of laser-ablated NaBr- and citrate-stabilized AuNPs with sizes of 5 nm. This systematic comparison is possible due to the fact that laser ablation in micromolar saline water gives access to narrowly distributed colloidal AuNPs without organic stabilizers. The Gibbs free energy of adsorption was determined to be of similar order for both AuNP batches (ca. -40 kJ/mol). The surface concentration of MPS, however, differed strongly and was more than 30% higher for NaBr-stabilized AuNP than for citrate-stabilized AuNP. Compared to planar Au substrates, the surface concentration of MPS on NaBr-AuNP suggests formation of a complete monolayer of MPS and demonstrates the fast functionalization of ligand-free AuNP up to monolayer coverage. On citrate-AuNP, however, an MPS coverage of only two-thirds of a monolayer is observed, which indicates that citrate partially resists functionalization and is mostly exchanged at low-coordinated Au surface sites. High surface coverage, however, is often closely linked to functionality, for example, when avidity effects are exploited during conjugate-receptor interactions. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b07897
  • 2018 • 218 Recent Advances in Thermo-, Photo-, and Electrocatalytic Glycerol Oxidation
    Dodekatos, G. and Schünemann, S. and Tüysüz, H.
    ACS Catalysis 8 6301-6333 (2018)
    Glycerol is a highly versatile molecule because of its three hydroxyl groups and can be transformed to a plethora of different value-added fine chemicals and products. It is an important byproduct in biodiesel production and, hence, produced in high amounts, which resulted in a high surplus flooding the market over the last decades. Thus, glycerol is regarded as a potential platform chemical, and many research efforts were devoted to find active catalysts to transform glycerol to various products via different catalytic processes. The selective oxidation reaction is one of the most promising reaction pathways to produce valuable fine chemicals used in the chemical and pharmaceutical industry. This Review describes the recent developments in selective glycerol oxidation to value-added products over heterogeneous catalysts. Particular emphasis is placed not only on newly developed catalysts based on supported noble-metal nanoparticles but also on catalysts containing nonprecious metals. The idea of using cost-efficient non-noble metals for glycerol oxidation is appealing from an economic point of view. Numerous parameters can influence the catalytic performance of the materials, which can be tuned by various synthetic approaches. The reasons for enhancements in activity are critically examined and put into perspective among the various studies. Moreover, during the past decade, many research groups also reported photocatalytic and, more scarcely, electrocatalytic pathways for glycerol oxidation, which are also described in detail herein and have otherwise found little attention in other reviews. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.8b01317
  • 2018 • 217 Oxide dispersion-strengthened alloys generated by laser metal deposition of laser-generated nanoparticle-metal powder composites
    Doñate-Buendía, C. and Frömel, F. and Wilms, M.B. and Streubel, R. and Tenkamp, J. and Hupfeld, T. and Nachev, M. and Gökce, E. and Weisheit, A. and Barcikowski, S. and Walther, F. and Schleifenbaum, J.H. and Gökce, B.
    Materials and Design 154 360-369 (2018)
    A new method is proposed for producing nanoparticle-metal composite powders for laser additive manufacturing of oxide-dispersion strengthened (ODS) alloys. Different composite powders containing laser-generated Y2O3 and yttrium iron garnet (YIG) nanoparticles were produced and consolidated by Laser Metal Deposition (LMD). The structural properties of the manufactured ODS alloys were analyzed, and their hardness, remnant porosity, and temperature-dependent compression behavior were characterized to study the effect of the composition and size of the nanoparticles on the structural and mechanical properties. While the structural analyses did not show significant differences between the processed samples within the limits of the characterization methods that were used, the temperature-dependent compression behavior showed an increase of up to 22 ± 11% in the high-temperature strength of the specimens that contained only 0.08 wt% of laser-generated nanoparticles. This increase is attributed to the dispersed and deagglomerated nature of the nanoparticles that were used during the powder-preparation step. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2018.05.044
  • 2018 • 216 Bifunctional Oxygen Reduction/Oxygen Evolution Activity of Mixed Fe/Co Oxide Nanoparticles with Variable Fe/Co Ratios Supported on Multiwalled Carbon Nanotubes
    Elumeeva, K. and Kazakova, M.A. and Morales, D.M. and Medina, D. and Selyutin, A. and Golubtsov, G. and Ivanov, Y. and Kuznetzov, V. and Chuvilin, A. and Antoni, H. and Muhler, M. and Schuhmann, W. and Masa, J.
    ChemSusChem 11 1204-1214 (2018)
    A facile strategy is reported for the synthesis of Fe/Co mixed metal oxide nanoparticles supported on, and embedded inside, high purity oxidized multiwalled carbon nanotubes (MWCNTs) of narrow diameter distribution as effective bifunctional catalysts able to reversibly drive the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline solutions. Variation of the Fe/Co ratio resulted in a pronounced trend in the bifunctional ORR/OER activity. Controlled synthesis and in-depth characterization enabled the identification of an optimal Fe/Co composition, which afforded a low OER/OER reversible overvoltage of only 0.831 V, taking the OER at 10 mA cm−2 and the ORR at −1 mA cm−2. Importantly, the optimal catalyst with a Fe/Co ratio of 2:3 exhibited very promising long-term stability with no evident change in the potential for both the ORR and the OER after 400 charge/discharge (OER/ORR) cycles at 15 mA cm−2 in 6 m KOH. Moreover, detailed investigation of the structure, size, and phase composition of the mixed Fe/Co oxide nanoparticles, as well as their localization (inside of or on the surface of the MWCNTs) revealed insight of the possible contribution of the individual catalyst components and their synergistic interaction in the catalysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cssc.201702381
  • 2018 • 215 Tailoring metal oxide nanoparticle dispersions for inkjet printing
    Gebauer, J.S. and Mackert, V. and Ognjanović, S. and Winterer, M.
    Journal of Colloid and Interface Science 526 400-409 (2018)
    There is a growing interest in science and industry for printed electronics. Printed electronics enable the production of large quantities of electronic components at low cost. Even though organic semiconductors are already widely used for printed components, inorganic materials may be advantageous due to their higher durability and superior device performance. Nevertheless, inorganic materials still remain difficult to print making the development of printable and functional inks a necessity. In this work we present the formulation, inkjet printing and processing of newly developed inks based on ethylene glycol as dispersion medium. Different metal oxide nanoparticles (ZnO, TiO2, CuO, SnO2 and In2O3) with high crystallinity and narrow size distribution were produced by chemical vapor synthesis. The particles were stabilized and the colloidal stability was evaluated by a combination of DLVO simulations and dynamic light scattering measurements. Measurements of rheological and interfacial properties, like viscosity and surface tension, are used to determine the printability on the basis of the inverse Ohnesorge number. Inks, developed in this work, have adjustable rheological properties as well as long-term stabilities without particle sedimentation over a period of several months. They are suitable for printing on different substrate materials like silicon and flexible polymeric substrates. © 2018 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2018.05.006
  • 2018 • 214 Influence of Chain Length and Branching on the Structure of Functionalized Gold Nanoparticles
    Giri, A.K. and Spohr, E.
    Journal of Physical Chemistry C 122 26739-26747 (2018)
    Functionalized gold nanoparticles (GNPs) in aqueous NaCl solutions have been studied using molecular dynamics simulations to assess the suitability of various functionalization chemistries to effectively shield the metallic core. Alkane thiol chains of various chain length (Cl) containing 6, 12, 18, and 24 carbon atoms are grafted onto the surface of the gold core. We compare the properties of GNPs functionalized with nonpolar CH3-terminated and polar COO-- and NH3 +-terminated chains, where the nanoparticle charge is compensated by appropriate numbers of excess Na+ or Cl- counterions. In addition to linear chains, we also investigate branched Y-shaped chains with the branching sites at the 4th, 8th, or 12th carbon atom from the sulfur atom that connects the chain to the gold core. The penetration depth of water and ions into the diffuse hydrocarbon shell region and its dependence on chain length, branching, and terminating group is found to increase with decreasing chain length irrespective of termination. Long linear chains, however, tend to form bundles independent of terminal group and can thus leave fractions of the nanoparticle surface exposed to small molecules, whereas shorter and branched chains do not form bundles and can cover the GNPs more homogeneously. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b08590
  • 2018 • 213 Shape-Dependent Dissolution and Cellular Uptake of Silver Nanoparticles
    Graf, C. and Nordmeyer, D. and Sengstock, C. and Ahlberg, S. and Diendorf, J. and Raabe, J. and Epple, M. and Köller, M. and Lademann, J. and Vogt, A. and Rancan, F. and Rühl, E.
    Langmuir 34 1506-1519 (2018)
    The cellular uptake and dissolution of trigonal silver nanoprisms (edge length 42 ± 15 nm, thickness 8 ± 1 nm) and mostly spherical silver nanoparticles (diameter 70 ± 25 nm) in human mesenchymal stem cells (hMSC's) and human keratinocytes (HaCaT cells) were investigated. Both particles are stabilized by polyvinylpyrrolidone (PVP), with the prisms additionally stabilized by citrate. The nanoprisms dissolved slightly in pure water but strongly in isotonic saline or at pH 4, corresponding to the lowest limit for the pH during cellular uptake. The tips of the prisms became rounded within minutes due to their high surface energy. Afterward, the dissolution process slowed down due to the presence of both PVP stabilizing Ag{100} sites and citrate blocking Ag{111} sites. On the contrary, nanospheres, solely stabilized by PVP, dissolved within 24 h. These results correlate with the finding that particles in both cell types have lost >90% of their volume within 24 h. hMSC's took up significantly more Ag from nanoprisms than from nanospheres, whereas HaCaT cells showed no preference for one particle shape. This can be rationalized by the large cellular interaction area of the plateletlike nanoprisms and the bending stiffness of the cell membranes. hMSC's have a highly flexible cell membrane, resulting in an increased uptake of plateletlike particles. HaCaT cells have a membrane with a 3 orders of magnitude higher Young's modulus than for hMSC. Hence, the energy gain due to the larger interaction area of the nanoprisms is compensated for by the higher energy needed for cell membrane deformation compared to that for spheres, leading to no shape preference. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03126
  • 2018 • 212 A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering
    Hupfeld, T. and Laumer, T. and Stichel, T. and Schuffenhauer, T. and Heberle, J. and Schmidt, M. and Barcikowski, S. and Gökce, B.
    Procedia CIRP 74 244-248 (2018)
    The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
    view abstractdoi: 10.1016/j.procir.2018.08.103
  • 2018 • 211 Determination of pore size gradients of virus filtration membranes using gold nanoparticles and their relation to fouling with protein containing feed streams
    Kosiol, P. and Müller, M.T. and Schneider, B. and Hansmann, B. and Thom, V. and Ulbricht, M.
    Journal of Membrane Science 548 598-608 (2018)
    Virus filtration membranes contribute to the virus safety of biopharmaceutical drugs due to their capability to retain virus particles mainly based on size-exclusion mechanisms. Typical product molecules like monoclonal antibodies with 9–12 nm in hydrodynamic diameter have to be transmitted by >95% while small viruses, e.g. parvoviridae (B19, MVM, PPV) with a diameter of 18–26 nm, have to be retained by at least 99.99%. Therefore, membrane fouling caused by product aggregates, which are similar in size compared to the viruses that have to be retained, is a common observation. Minimal membrane fouling is a requirement for economical processes and is influenced by both the membrane surface chemistry and the membrane structure, particularly with regard to the pore size gradient (PSG). In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine PSGs for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. GNP adsorption to the membrane material was suppressed by the use of an anionic surfactant, allowing to gain insights into size-exclusion properties of the membranes. Membrane performance with regard to fouling was further investigated by determination of protein mass throughputs up-to a defined membrane flux decay using solutions containing intravenous immunoglobulin (IVIG) as model protein. Additionally, the fouling mechanism of IVIG was investigated and confirmed to be caused by trace amounts of species larger than IVIG monomers and dimers, which were already present in the feed. The fouling results are discussed in relationship to the determined PSGs, since the porous support structure of virus filtration membranes can act as a depth pre-filter protecting the separation-active layer from particulate foulants. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.11.048
  • 2018 • 210 Rapid and sensitive SERS detection of the cytokine tumor necrosis factor alpha (tnf-α) in a magnetic bead pull-down assay with purified and highly Raman-active gold nanoparticle clusters
    Lai, Y. and Schlücker, S. and Wang, Y.
    Analytical and Bioanalytical Chemistry 410 5993-6000 (2018)
    Tumor necrosis factor alpha (TNF-α) is a cytokine with significance in early diagnosis of cardiovascular diseases, obesity and insulin resistance. We demonstrate the proof of concept for a rapid and sensitive detection of TNF-α using a magnetic bead pull-down assay in combination with surface-enhanced Raman scattering (SERS). The use of purified and highly SERS-active small clusters of gold nanoparticles (AuNP) provides the high sensitivity of the assay with a limit of detection of ca. 1 pg/mL. Continuous density gradient centrifugation was employed for separating the very bright silica-encapsulated AuNP dimers and trimers from the significantly weaker AuNP monomers. Negative control experiments with other cytokines (IL-6, IL-8) and bovine serum albumin (BSA) confirm the high specificity of the assay, but indicate also space for future improvements by further reducing non-specific binding between proteins and the SERS nanotags. The multiplexing potential of this SERS-based detection scheme is exemplarily demonstrated by using a set of three spectrally distinct and highly SERS-active AuNP clusters with unique spectral barcodes. [Figure not available: see fulltext.]. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00216-018-1218-0
  • 2018 • 209 Primary particle diameter differentiation and bimodality identification by five analytical methods using gold nanoparticle size distributions synthesized by pulsed laser ablation in liquids
    Letzel, A. and Gökce, B. and Menzel, A. and Plech, A. and Barcikowski, S.
    Applied Surface Science 435 743-751 (2018)
    For a known material, the size distribution of a nanoparticle colloid is a crucial parameter that defines its properties. However, measured size distributions are not easy to interpret as one has to consider weighting (e.g. by light absorption, scattering intensity, volume, surface, number) and the way size information was gained. The radius of a suspended nanoparticle can be given as e.g. sphere equivalent, hydrodynamic, Feret or radius of gyration. In this study, gold nanoparticles in water are synthesized by pulsed-laser ablation (LAL) and fragmentation (LFL) in liquids and characterized by various techniques (scanning transmission electron microscopy (STEM), small-angle X-ray scattering (SAXS), analytical disc centrifugation (ADC), dynamic light scattering (DLS) and UV–vis spectroscopy with Mie-Gans Theory) to study the comparability of different analytical techniques and determine the method that is preferable for a given task related to laser-generated nanoparticles. In particular, laser-generated colloids are known to be bimodal and/or polydisperse, but bimodality is sometimes not analytically resolved in literature. In addition, frequently reported small size shifts of the primary particle mode around 10 nm needs evaluation of its statistical significance related to the analytical method. Closely related to earlier studies on SAXS, different colloids in defined proportions are mixed and their size as a function of the nominal mixing ratio is analyzed. It is found that the derived particle size is independent of the nominal mixing ratio if the colloid size fractions do not overlap considerably. Conversely, the obtained size for colloids with overlapping size fractions strongly depends on the nominal mixing ratio since most methods cannot distinguish between such fractions. Overall, SAXS and ADC are very accurate methods for particle size analysis. Further, the ability of different methods to determine the nominal mixing ratio of sizes fractions is studied experimentally. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.11.130
  • 2018 • 208 Discovery of a Multinary Noble Metal–Free Oxygen Reduction Catalyst
    Löffler, T. and Meyer, H. and Savan, A. and Wilde, P. and Garzón Manjón, A. and Chen, Y.-T. and Ventosa, E. and Scheu, C. and Ludwig, Al. and Schuhmann, W.
    Advanced Energy Materials 8 (2018)
    In the endeavor of discovering new noble metal–free electrocatalysts for the oxygen reduction reaction, noble metal–free multinary transition metal nanoparticle libraries are investigated. The complexity of such multiple principal element alloys provides access to a large variety of different elemental compositions, each with potentially unique properties. The strategy for efficient identification of novel electrocatalytically active systems comprises combinatorial co-sputtering into an ionic liquid followed by potential-assisted immobilization of the formed nanoparticles at a microelectrode which allows the evaluation of their intrinsic electrocatalytic activity in alkaline media. A surprisingly high intrinsic activity is found for the system Cr–Mn–Fe–Co–Ni, which is at least comparable to Pt under the same conditions, an unexpected result based on the typical properties of its constituents. Systematic removal of each element from the quinary alloy system yields a significant drop in activity for all quaternary alloys, indicating the importance of the synergistic combination of all five elements, likely due to formation of a single solid solution phase with altered properties which enables the limitations of the single elements to be overcome. Multinary transition metal alloys as a novel material class in electrocatalysis with basically unlimited possibilities for catalyst design, targeting the replacement of noble metal–based materials, are suggested. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/aenm.201802269
  • 2018 • 207 Silver nanoparticles in complex media: An easy procedure to discriminate between metallic silver nanoparticles, reprecipitated silver chloride, and dissolved silver species
    Loza, K. and Epple, M.
    RSC Advances 8 24386-24391 (2018)
    Silver nanoparticles undergo oxidative dissolution in water upon storage. This occurs in pure water as well as in more complex media, including natural environments, biological tissues, and cell culture media. However, the dissolution leads to the reprecipitation of silver chloride as chloride is present in almost all relevant environments. The discrimination between dissolved silver species (ions and silver complexes) and dispersed (solid) species does not take this into account because all solid species (metallic silver and silver chloride) are isolated together. By applying a chemical separation procedure, we show that it is possible to quantify silver, silver chloride, and dissolved silver species after immersion into a typical cell culture medium (DMEM + 10% FCS). During the dissolution of metallic silver nanoparticles, about half of the dissolved silver is reprecipitated as solid silver chloride, i.e. the mere analysis of the soluble silver species does not reflect the true situation. The separation protocol is suitable for all chloride-containing media in the presence or in the absence of biomolecules. © 2018 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c8ra04500c
  • 2018 • 206 Structure and size dependence of the magnetic properties of Ni@C nanocomposites
    Manukyan, A. and Elsukova, A. and Mirzakhanyan, A. and Gyulasaryan, H. and Kocharian, A. and Sulyanov, S. and Spasova, M. and Römer, F. and Farle, M. and Sharoyan, E.
    Journal of Magnetism and Magnetic Materials 467 150-159 (2018)
    Carbon-coated nickel (Ni) nanoparticles, Ni@C nanocomposites, have been synthesized using solid-state pyrolysis of nickel phthalocyanine and metal-free phthalocyanine (NiPc)x· (H2Pc)1−x solid solutions, 0⩽x⩽1. The Ni concentrations in carbon matrix (cNi) of the prepared samples continuously varied in the range of 0–3at.% (0–12wt.%). The average nanoparticle size varied within 4–40 nm range. All samples containing single domain Ni nanoparticles exhibit both ferromagnetic and superparamagnetic properties because of the wide range of size distribution. An abrupt drop of saturation magnetization has been observed with decrease in size of Ni nanoparticles from 40 nm to 12 nm. Nearly linear dependence of saturation magnetization on the nanoparticle surface/volume ratio can be interpreted as a result of contact interaction between Ni nanoparticles and the carbon matrix which provides an electron transfer from carbon matrix to nickel. However, further reductions in nanoparticle size increase magnetization growth of which can apparently contribute to the emergence of the giant paramagnetism due to large orbital moments of conductive electrons. The size effects and surface magnetic anisotropy in Ni@C nanocomposites are revealed in the measurements of coercive field, zero-field cooling (ZFC) susceptibility, blocking temperatures and ferromagnetic resonance spectra. Concentration dependencies of ferromagnetic and electron paramagnetic resonance parameters in Ni@C nanocomposites have also been investigated and their peculiarities highlighted. A correlation between concentration dependencies of FMR and SQUID magnetometry parameters, namely between the g-factor curves – geff, the resonance linewidth – ΔHFMR and coercive field – Hc, have been observed. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.jmmm.2018.07.056
  • 2018 • 205 Structural Engineering of 3D Carbon Materials from Transition Metal Ion-Exchanged y Zeolite Templates
    Moon, G.-H. and Bähr, A. and Tüysüz, H.
    Chemistry of Materials 30 3779-3788 (2018)
    A series of three-dimensional ordered microporous carbon materials (3D CMs) were prepared through a nanocasting route by using transition metal ion-exchanged Y zeolite (M-Y) as template and ethylene gas a carbon source. The different d-π coordination and the formation of metal nanoparticles during thermal treatment altered textural parameters of the final carbon products. After a detailed structural analysis and characterization, the most promising cobalt-carbon sample was further treated with NH3 for nitrogen doping and evaluated for oxygen reduction reaction (ORR). This new class of material indicated good electrochemical stability and similar activity in comparison with those of commercial Pt/C (20 wt %) electrocatalyst. The protocol developed here allows in situ incorporation of diverse transition metals as well as the doping of various heteroelements into a three-dimensional carbon framework and has great potential for different catalytic applications. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.chemmater.8b00861
  • 2018 • 204 Oxygen Reduction Activity and Reversible Deactivation of Single Silver Nanoparticles during Particle Adsorption Events
    Öhl, D. and Clausmeyer, J. and Barwe, S. and Botz, A. and Schuhmann, W.
    ChemElectroChem 5 1886-1890 (2018)
    The activity towards the oxygen reduction reaction (ORR) of single silver nanoparticles (AgNP) was quantified by using AgNP impacts on dual-bore carbon nanoelectrodes in highly alkaline media. We found suitable conditions for the particles to adhere sufficiently stably for detailed electrochemical characterization of a single particle. The special electrode design opens the possibility to dose gaseous oxygen to the nanoparticle under study. Deactivation of the catalytic activity of the AgNP upon excessive exposure to oxygen as well as the recovery of catalytic activity under reducing conditions is presumably attributed to hydrogen evolution at the applied low potentials. The proposed approach allows mechanistic parameters for the ORR to be extracted at a single AgNP in highly alkaline media in the absence of any binder materials and under exclusion of averaging ensemble effects. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800094
  • 2018 • 203 Crystallographic characterization of laser-generated, polymer-stabilized 4 nm silver-gold alloyed nanoparticles
    Prymak, O. and Jakobi, J. and Rehbock, C. and Epple, M. and Barcikowski, S.
    Materials Chemistry and Physics 207 442-450 (2018)
    Monometallic silver and gold nanoparticles and bimetallic silver-gold (AgAu) nanoparticles were prepared by laser ablation in liquids in the atomic composition range of Ag:Au from 0:100 to 100:0 with steps of 10 at% and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). As metallic bulk targets for laser ablation, pure silver, pure gold, and alloyed AgAu foils with the desired composition were used. Size separation by centrifugation and freeze-drying gave monodisperse spherical nanoparticles with a diameter of 4 nm as determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). A crystallographic characterization of the nanoparticles was carried out by X-ray powder diffraction (XRD) and Rietveld refinement, leading to highly precise cubic lattice parameters (fcc crystal system) and crystallite sizes. For comparison, the same analysis including the determination of the microstrain was carried out for the bulk target materials (AgAu alloys in the full concentration range). Both nanoparticles and bulk target materials obeyed Vegard's rule, with only slight deviations. The fact that the crystallite size as determined by XRD was identical to the hydrodynamic diameter by DCS and the Feret diameter by TEM indicates that the particles consist of only one domain, i.e. they are single crystals. The combination of UV-vis spectroscopy with energy-dispersive X-ray spectroscopy (EDX) as line scan along the nanoparticle showed a homogenous distribution of the gold and silver inside the nanoparticles, indicating solid solution alloys, in contrast to what was observed earlier for chemically prepared AgAu nanoparticles by reduction of metal ions in water. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2017.12.080
  • 2018 • 202 Two mechanisms of nanoparticle generation in picosecond laser ablation in liquids: The origin of the bimodal size distribution
    Shih, C.-Y. and Streubel, R. and Heberle, J. and Letzel, A. and Shugaev, M.V. and Wu, C. and Schmidt, M. and Gökce, B. and Barcikowski, S. and Zhigilei, L.V.
    Nanoscale 10 6900-6910 (2018)
    The synthesis of chemically clean and environmentally friendly nanoparticles through pulsed laser ablation in liquids has shown a number of advantages over conventional chemical synthesis methods and has evolved into a thriving research field attracting laboratory and industrial applications. The fundamental understanding of processes leading to the nanoparticle generation, however, still remains elusive. In particular, the origin of bimodal nanoparticle size distributions in femto- and picosecond laser ablation in liquids, where small nanoparticles (several nanometers) with narrow size distribution are commonly observed to coexist with larger (tens to hundreds of nanometers) ones, has not been explained so far. In this paper, joint computational and experimental efforts are applied to understand the mechanisms of nanoparticle formation in picosecond laser ablation in liquids and to explain the bimodal nanoparticle size distributions. The results of a large-scale atomistic simulation reveal the critical role of the dynamic interaction between the ablation plume and the liquid environment, leading to the generation of large nanoparticles through a sequence of hydrodynamic instabilities at the plume-liquid interface and a concurrent nucleation and growth of small nanoparticles in an expanding metal-liquid mixing region. The computational predictions are supported by a series of stroboscopic videography experiments showing the emergence of small satellite bubbles surrounding the main cavitation bubble generated in single pulse experiments. Carefully timed double pulse irradiation triggers expansion of secondary cavitation bubbles indicating, in accord with the simulation results, the presence of localized sites of laser energy deposition (possibly large nanoparticles) injected into the liquid at the early stage of the bubble formation. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7nr08614h
  • 2018 • 201 Synthesis of rare-earth metal and rare-earth metal-fluoride nanoparticles in ionic liquids and propylene carbonate
    Siebels, M. and Mai, L. and Schmolke, L. and Schütte, K. and Barthel, J. and Yue, J. and Thomas, J. and Smarsly, B.M. and Devi, A. and Fischer, R.A. and Janiak, C.
    Beilstein Journal of Nanotechnology 9 1881-1894 (2018)
    Decomposition of rare-earth tris(N, N'-diisopropyl-2-methylamidinato)metal(III) complexes [RE(MeC(N(iPr)2))3] (RE(amd)3; RE = Pr(III), Gd(III), Er(III)) and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium(III) (Eu(dpm)3) induced by microwave heating in the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIm][NTf2]) and in propylene carbonate (PC) yield oxide-free rare-earth metal nanoparticles (RE-NPs) in [BMIm][NTf2] and PC for RE = Pr, Gd and Er or rare-earth metal-fluoride nanoparticles (REF3-NPs) in the fluoridedonating IL [BMIm][BF4] for RE = Pr, Eu, Gd and Er. The crystalline phases and the absence of significant oxide impurities in RE-NPs and REF3-NPs were verified by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED) and highresolution X-ray photoelectron spectroscopy (XPS). The size distributions of the nanoparticles were determined by transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to an average diameter of (11 ± 6) to (38 ± 17) nm for the REF3-NPs from [BMIm][BF4]. The RE-NPs from [BMIm][NTf2] or PC showed diameters of (1.5 ± 0.5) to (5 ± 1) nm. The characterization was completed by energy-dispersive X-ray spectroscopy (EDX). © 2018 Siebels et al.
    view abstractdoi: 10.3762/bjnano.9.180
  • 2018 • 200 Atomic-Scale Explanation of O2 Activation at the Au-TiO2 Interface
    Siemer, N. and Lüken, A. and Zalibera, M. and Frenzel, J. and Muñoz-Santiburcio, D. and Savitsky, A. and Lubitz, W. and Muhler, M. and Marx, D. and Strunk, J.
    Journal of the American Chemical Society 140 18082-18092 (2018)
    By a combination of electron paramagnetic resonance spectroscopy, finite-temperature ab initio simulations, and electronic structure analyses, the activation of molecular dioxygen at the interface of gold nanoparticles and titania in Au/TiO2 catalysts is explained at the atomic scale by tracing processes down to the molecular orbital picture. Direct evidence is provided that excess electrons in TiO2, for example created by photoexcitation of the semiconductor, migrate to the gold particles and from there to oxygen molecules adsorbed at gold/titania perimeter sites. Superoxide species are formed more efficiently in this way than on the bare TiO2 surface. This catalytic effect of the gold nanoparticles is attributed to a weakening of the internal O-O bond, leading to a preferential splitting of the molecule at shorter bond lengths together with a 70% decrease of the dissociation free energy barrier compared to the non-catalyzed case on bare TiO2. The findings are an important step forward in the clarification of the role of gold in (photo)catalytic processes. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/jacs.8b10929
  • 2018 • 199 Depositing laser-generated nanoparticles on powders for additive manufacturing of oxide dispersed strengthened alloy parts via laser metal deposition
    Streubel, R. and Wilms, M.B. and Doñate-Buendía, C. and Weisheit, A. and Barcikowski, S. and Schleifenbaum, J.H. and Gökce, B.
    Japanese Journal of Applied Physics 57 (2018)
    We present a novel route for the adsorption of pulsed laser-dispersed nanoparticles onto metal powders in aqueous solution without using any binders or surfactants. By electrostatic interaction, we deposit Y2O3 nanoparticles onto iron-chromium based powders and obtain a high dispersion of nano-sized particles on the metallic powders. Within the additively manufactured component, we show that the particle spacing of the oxide inclusion can be adjusted by the initial mass fraction of the adsorbed Y2O3 particles on the micropowder. Thus, our procedure constitutes a robust route for additive manufacturing of oxide dispersion-strengthened alloys via oxide nanoparticles supported on steel micropowders. © 2018 The Japan Society of Applied Physics.
    view abstractdoi: 10.7567/JJAP.57.040310
  • 2018 • 198 High resolution, binder-free investigation of the intrinsic activity of immobilized NiFe LDH nanoparticles on etched carbon nanoelectrodes
    Wilde, P. and Barwe, S. and Andronescu, C. and Schuhmann, W. and Ventosa, E.
    Nano Research 11 6034-6044 (2018)
    The determination of the intrinsic properties of nanomaterials is essential for their optimization as electrocatalysts, however it poses great challenges from the standpoint of analytical tools and methods. Herein, we report a novel methodology that allows for a binder-free investigation of electrocatalyst nanoparticles. The potential-assisted immobilization of a non-noble metal catalyst, i.e., nickel-iron layered double hydroxide (NiFe LDH) nanoparticles, was employed to directly attach small nanoparticle ensembles from a suspension to the surface of etched carbon nanoelectrodes. The dimensions of this type of electrodes allowed for the immobilization of the catalyst material below the picogram scale and resulted in a high resolution towards the faradaic current response. In addition the effect of the electrochemical aging on the intrinsic activity of the catalyst was investigated in alkaline media by means of continuous cyclic voltammetry. A change in the material properties could be observed, which was accompanied by a substantial decrease in its intrinsic activity. [Figure not available: see fulltext.] © 2018, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s12274-018-2119-4
  • 2018 • 197 Laser additive manufacturing of oxide dispersion strengthened steels using laser-generated nanoparticle-metal composite powders
    Wilms, M.B. and Streubel, R. and Frömel, F. and Weisheit, A. and Tenkamp, J. and Walther, F. and Barcikowski, S. and Schleifenbaum, J.H. and Gökce, B.
    Procedia CIRP 74 196-200 (2018)
    A new route for the synthesis of powder composites suitable for processing with laser additive manufacturing is demonstrated. The powder composites, consisting of micrometer-sized stainless steel powder, homogenously decorated with nano-scaled Y2O3 powder particles, are manufactured by laser processing of colloids and electrostatic deposition. Consolidated by laser metal deposition and selective laser melting, the resulting specimens show superior mechanical properties at elevated temperatures, caused by the nano-sized, homogenously distributed dispersoids. © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.
    view abstractdoi: 10.1016/j.procir.2018.08.093
  • 2018 • 196 Simultaneous Rayleigh/Mie and Raman/Fluorescence Characterization of Molecularly Functionalized Colloids by Correlative Single-Particle Real-Time Imaging in Suspension
    Wissler, J. and Wehmeyer, M. and Bäcker, S. and Knauer, S. and Schlücker, S.
    Analytical Chemistry 90 723-728 (2018)
    Many applications of nano- and microparticles require molecular functionalization. Assessing the heterogeneity of a colloidal sample in terms of its molecular functionalization is highly desirable but not accessible by conventional ensemble experiments. Retrieving this information necessitates single-particle experiments which simultaneously detect both functionalized and nonfunctionalized particles via two separate imaging channels. In this contribution, we present an optical setup for performing correlative single-particle imaging using laser light-sheet illumination: the first detection channel records elastic light scattering (Rayleigh/Mie), while the second channel detects inelastic light scattering (Raman) or fluorescence. The instrument is tested with Raman reporter-functionalized SERS-active metal nanoparticles (core/satellite silver nanoparticles, dimers and monomers of gold nanoparticles) and fluorophore-functionalized colloids (fluorescent polymer microparticles, dye-labeled protein on gold nanoparticles). © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.7b02528
  • 2018 • 195 Simultaneous Opto- and Spectro-Electrochemistry: Reactions of Individual Nanoparticles Uncovered by Dark-Field Microscopy
    Wonner, K. and Evers, M.V. and Tschulik, K.
    Journal of the American Chemical Society 140 12658-12661 (2018)
    Despite the frequent use of silver nanoparticles in consumer products and medical treatments, their reactivity and degradation in aqueous suspensions are still under debate. Here we elucidate this reactivity by an in situ opto- and spectro-electrochemical approach. Using dark-field microscopy coupled to a spectrophotometer and to an electrochemical cell, redox reactions of individual silver nanoparticles are studied in the presence of chloride. The intensity and spectral position of the plasmon resonance of an individual particle are tracked simultaneously in real time during cyclic voltammetry. They both change almost instantaneously with the detected current in a chemically reversible way. Thus, it is evidenced that the intensity decrease of the optical signal at the silver peak position is caused by the reversible formation of silver chloride and not by dissolution of silver. Moreover, at large positive potentials, further transformation to silver oxide or chlorite is revealed spectroscopically, although the electrochemical current is hidden by water and chloride oxidation. Thus, the combination of electrochemistry with dark-field microscopy and hyperspectral imaging is introduced as a new tool for real-time analysis of (electro-)chemical reactions of nanoparticles on a single-entity level. Copyright © 2018 American Chemical Society.
    view abstractdoi: 10.1021/jacs.8b02367
  • 2018 • 194 On the nature of spillover hydrogen species on platinum/nitrogen-doped mesoporous carbon composites: A temperature-programmed nitrobenzene desorption study
    Yang, F. and Hu, B. and Xia, W. and Peng, B. and Shen, J. and Muhler, M.
    Journal of Catalysis 365 55-62 (2018)
    Spillover hydrogen species were generated by dissociative H2 adsorption on Pt nanoparticles supported on nitrogen-doped mesoporous carbon. The spillover hydrogen species on the support can migrate back to the Pt nanoparticles and hydrogenate subsequently adsorbed nitrobenzene to aniline at 80 °C, which was detected during temperature-programmed desorption experiments from 80 to 300 °C in pure He. The amount of spillover hydrogen can be tuned mainly by the pre-reduction temperature rather than by other parameters. The absence of aniline formation during nitrobenzene desorption experiments in the presence of CO indicates that hydrogenation occurs exclusively on Pt and that the spillover hydrogen species are present on the carbon support in a chemically inactive state. Most likely, spillover hydrogen is reversibly stored on the carbon support as adsorbed protons on the surface and as electrons in the bulk. These findings provide a new perspective on Pt/C-based hydrogen storage materials and fuel cell catalysts. © 2018
    view abstractdoi: 10.1016/j.jcat.2018.06.020
  • 2018 • 193 Effect of Antigen Retrieval Methods on Nonspecific Binding of Antibody-Metal Nanoparticle Conjugates on Formalin-Fixed Paraffin-Embedded Tissue
    Zhang, Y. and Wang, X.-P. and Perner, S. and Bankfalvi, A. and Schlücker, S.
    Analytical Chemistry 90 760-768 (2018)
    Immunohistochemical analysis of formalin-fixed paraffin-embedded (FFPE) tissues provides important diagnostic and prognostic information in pathology. Metal nanoparticles (NPs) and, in particular, surface-enhanced Raman scattering (SERS) nanotags as a new class of labeling reagents are promising to be used for multiplexed protein profiling on tissue sections. However, nonspecific binding of NPs onto the tissue specimens greatly hampers their clinical applications. In this study, we found that the antigen retrieval method strongly influences the extent of nonspecific binding of the antibody-SERS NP conjugates to the tissue. Our SERS labels comprised ca. 70 nm Au nanostars coated with ethylene glycol-modified Raman reporter molecules for hydrophilic stabilization and subsequent covalent bioconjugation to antibodies. We systematically investigated the influence of heat- and protease-induced epitope retrieval (HIER and PIER, respectively) on the immunostaining quality of prostate-specific antigen (PSA) on human prostate tissue sections. The best staining results were obtained with PIER. Pretreatment of the tissue sections by HIER led to selective but nonspecific adsorption of the antibody-Au nanostar conjugates onto epithelial cells, while enzymatic treatment within PIER did not. In addition to gold nanostars, also other types of metal NPs with different shapes and sizes (including ca. 20 nm quasi-spherical Au NPs and ca. 60 nm quasi-spherical Au/Ag nanoshells) as well as tissue sections from different organs (including prostate and breast) were tested; in each case the same tendency was observed, i.e., PIER yielded better results than HIER. Therefore, we recommend PIER for future NP-based tissue immunostaining such as immuno-SERS microscopy. Alternatively, for antigens that can only be unmasked by heating, PEGylation of the NPs is recommended to avoid nonspecific binding. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.7b03144
  • 2018 • 192 Laser Fragmentation of Colloidal Gold Nanoparticles with High-Intensity Nanosecond Pulses is Driven by a Single-Step Fragmentation Mechanism with a Defined Educt Particle-Size Threshold
    Ziefuß, A.R. and Reichenberger, S. and Rehbock, C. and Chakraborty, I. and Gharib, M. and Parak, W.J. and Barcikowski, S.
    Journal of Physical Chemistry C 122 22125-22136 (2018)
    Laser-inducd fragmentation is a promising tool for controlling the particle size of ligand-free colloidal nanoparticles and to synthesize ligand-free gold nanoclusters. However, because the underlying mechanisms are not fully understood, increasing the yield of this process remains challenging. In this work, we examine the pulsed laser fragmentation of gold nanoparticles in liquid under statistical single-pulse conditions with high-fluence nanosecond pulses and correlate them with the educt particle size, number of pulses, and laser fluence. We conclusively prove that the fragmentation process of gold nanoparticles is a one-pulse and one-step event, which yields monomodal particles of 10 nm down to 2.8 +/- 0.1 nm when exceeding a pulse peak power of 1.6 × 1012 W/m2 and when all educt particles are larger than 13.4 nm. This size threshold for quantitative fragmentation fits well with the size limit of 13.1 nm calculated with respect to the evaporation-heat-energy balance. Furthermore, we found strong evidence that the number of irradiation cycles, varied within the regime of one to four laser pulses/colloid volume, can be used to tune the surface chemistry and surface charge of the resulting nanoparticles in an aqueous medium. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.8b04374
  • 2017 • 191 Metal–Organic Framework Derived Carbon Nanotube Grafted Cobalt/Carbon Polyhedra Grown on Nickel Foam: An Efficient 3D Electrode for Full Water Splitting
    Aijaz, A. and Masa, J. and Rösler, C. and Xia, W. and Weide, P. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    ChemElectroChem 4 188-193 (2017)
    The growth of metal–organic framework (ZIF-67) nanocrystals on nickel foam (NF), followed by carbonization in diluted H2, leads to a nitrogen-doped carbon-nanotube-grafted cobalt/carbon polyhedra film on NF. The obtained material serves as a highly active binder-free electrocatalyst for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), enabling high-performance alkaline (0.1 m KOH) water electrolysis with potentials of 1.62 and 0.24 V, respectively, at OER and HER current densities of 10 mA cm−2. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201600452
  • 2017 • 190 MOF-Templated Assembly Approach for Fe3C Nanoparticles Encapsulated in Bamboo-Like N-Doped CNTs: Highly Efficient Oxygen Reduction under Acidic and Basic Conditions
    Aijaz, A. and Masa, J. and Rösler, C. and Antoni, H. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    Chemistry - A European Journal (2017)
    Developing high-performance non-precious metal catalysts (NPMCs) for the oxygen-reduction reaction (ORR) is of critical importance for sustainable energy conversion. We report a novel NPMC consisting of iron carbide (Fe3C) nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes (b-NCNTs), synthesized by a new metal-organic framework (MOF)-templated assembly approach. The electrocatalyst exhibits excellent ORR activity in 0.1m KOH (0.89V at -1mAcm-2) and in 0.5m H2SO4 (0.73V at -1mAcm-2) with a hydrogen peroxide yield of below 1% in both electrolytes. Due to encapsulation of the Fe3C nanoparticles inside porous b-NCNTs, the reported NPMC retains its high ORR activity after around 70hours in both alkaline and acidic media. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201701389
  • 2017 • 189 Surface-Enhanced Raman Spectroscopy and Density Functional Theory Calculations of a Rationally Designed Rhodamine with Thiol Groups at the Xanthene Ring
    Brem, S. and Schlücker, S.
    Journal of Physical Chemistry C 121 15310-15317 (2017)
    Rhodamines are widely used dyes in fluorescence and surface-enhanced Raman spectroscopy (SERS). The latter requires adsorption of the dye onto the surface of plasmonic nanostructures, a process which requires attractive molecule-surface interactions. Here, we report an experimental SERS and computational density functional theory (DFT) study investigating the role of thiol functionalization at the xanthene ring of the rhodamine in the adsorption onto gold nanoparticles. For this purpose, a new bisthiolated rhodamine derivative was rationally designed and synthesized via a PPh3/I2 reduction route. The introduction of two thiol moieties directly at the xanthene ring provides the shortest possible distance between the molecular π-system and the metal surface for maximum SERS enhancement combined with the strong Au-S interaction for chemisorption. The comparison of experimental SERS spectra obtained from gold nanostars and a film of gold nanoparticles with results from DFT calculations (molecular electrostatic potential, normal modes) suggests adsorption via the thiol groups at the xanthene moiety. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.7b01504
  • 2017 • 188 Role of Composition and Size of Cobalt Ferrite Nanocrystals in the Oxygen Evolution Reaction
    Chakrapani, K. and Bendt, G. and Hajiyani, H. and Schwarzrock, I. and Lunkenbein, T. and Salamon, S. and Landers, J. and Wende, H. and Schlögl, R. and Pentcheva, R. and Behrens, M. and Schulz, S.
    ChemCatChem 9 2988-2995 (2017)
    Sub-10 nm CoFe2O4 nanoparticles with different sizes and various compositions obtained by (partial) substitution of Co with Ni cations have been synthesized by using a one-pot method from organic solutions by the decomposition of metal acetylacetonates in the presence of oleylamine. The electrocatalytic activity of CoFe2O4 towards the oxygen evolution reaction (OER) is clearly enhanced with a smaller size (3.1 nm) of the CoFe2O4 nanoparticles (compared with 4.5 and 5.9 nm). In addition, the catalytic activity is improved by partial substitution of Co with Ni, which also leads to a higher degree of inversion of the spinel structure. Theoretical calculations attribute the positive catalytic effect of Ni owing to the lower binding energy differences between adsorbed O and OH compared with pure cobalt or nickel ferrites, resulting in higher OER activity. Co0.5Ni0.5Fe2O4 exhibited a low overpotential of approximately 340 mV at 10 mA cm−2, a smaller Tafel slope of 51 mV dec−1, and stability over 30 h. The unique tunability of these CoFe2O4 nanocrystals provides great potential for their application as an efficient and competitive anode material in the field of electrochemical water splitting as well as for systematic fundamental studies aiming at understanding the correlation of composition and structure with performance in electrocatalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cctc.201700376
  • 2017 • 187 Experimental and Theoretical Understanding of Nitrogen-Doping-Induced Strong Metal-Support Interactions in Pd/TiO2 Catalysts for Nitrobenzene Hydrogenation
    Chen, P. and Khetan, A. and Yang, F. and Migunov, V. and Weide, P. and Stürmer, S.P. and Guo, P. and Kähler, K. and Xia, W. and Mayer, J. and Pitsch, H. and Simon, U. and Muhler, M.
    ACS Catalysis 7 1197-1206 (2017)
    By doping the TiO2 support with nitrogen, strong metal-support interactions (SMSI) in Pd/TiO2 catalysts can be tailored to obtain high-performance supported Pd nanoparticles (NPs) in nitrobenzene (NB) hydrogenation catalysis. According to the comparative studies by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance CO FTIR (CO-DRIFTS), N-doping induced a structural promoting effect, which is beneficial for the dispersion of Pd species on TiO2. High-angle annular dark-field scanning transmission electron microscopy study of Pd on N-doped TiO2 confirmed a predominant presence of sub-2 nm Pd NPs, which are stable under the applied hydrogenation conditions. XPS and CO-DRIFTS revealed the formation of strongly coupled Pd-N species in Pd/TiO2 with N-doped TiO2 as support. Density functional theory (DFT) calculations over model systems with Pdn (n = 1, 5, or 10) clusters deposited on TiO2(101) surface were performed to verify and supplement the experimental observations. In hydrogenation catalysis using NB as a model molecule, Pd NPs on N-doped TiO2 outperformed those on N-free TiO2 in terms of both catalytic activity and stability, which can be attributed to the presence of highly dispersed Pd NPs providing more active sites, and to the formation of Pd-N species favoring the dissociative adsorption of the reactant NB and the easier desorption of the product aniline. (Figure Presented). © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acscatal.6b02963
  • 2017 • 186 Water-free synthesis of ZnO quantum dots for application as an electron injection layer in light-emitting electrochemical cells
    Daumann, S. and Andrzejewski, D. and Di Marcantonio, M. and Hagemann, U. and Wepfer, S. and Vollkommer, F. and Bacher, G. and Epple, M. and Nannen, E.
    Journal of Materials Chemistry C 5 2344-2351 (2017)
    Large-area light emitters like organic (OLEDs) or quantum dot light-emitting devices (QLEDs) and light-emitting electrochemical cells (LECs) have gained increasing interest due to their cost-effective fabrication on various even flexible substrates. The implementation of ZnO nanoparticles as an electron injection layer in large-area emitters leads to efficient solution-based devices. However, ZnO support layers are frequently in direct contact with water-sensitive emitter materials, which requires ZnO nanoparticles with minimum water content. A water-free synthesis route (except for the small amount of water formed during the synthesis) of ligand-free ZnO nanoparticles is presented. The spherical ZnO nanoparticles have a diameter of 3.4 nm, possess a high crystallinity, and form stable dispersions in ethanol or 1-hexanol. Their application together with a transition metal complex (iTMC)-LEC as an additional electron injection layer resulted in an increase of the device efficiency from 1.6 to 2.4 lm W−1 as well as the reduction of the run-up time to one fifth, compared to the same system without ZnO nanoparticles. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6tc05571k
  • 2017 • 185 Spectroscopic models for laser-heated silicon and copper nanoparticles
    Daun, K. and Menser, J. and Mansmann, R. and Moghaddam, S.T. and Dreier, T. and Schulz, C.
    Journal of Quantitative Spectroscopy and Radiative Transfer 197 3-11 (2017)
    Interpreting laser-induced incandescence (LII) measurements on aerosolized nanoparticles requires a spectroscopic model that relates the measured spectral incandescence to the temperature of the nanoparticles. We present spectroscopic models for molten silicon and copper nanoparticles, which are evaluated through extinction and incandescence measurements on nanoaerosols. Measurements on molten silicon nanoparticles are consistent with the Drude theory in the Rayleigh limit of Mie theory. The copper nanoparticles were initially assumed to coalesce into spheres, but the observed spectral incandescence does not show a surface plasmon polariton (SPP) peak in the vicinity of 600. nm expected of spheres. A simulation based on the discrete dipole approximation (DDA) suggests that this effect could be explained by the structure of the copper aggregates. © 2016.
    view abstractdoi: 10.1016/j.jqsrt.2016.10.006
  • 2017 • 184 Dependence of the optical constants and the performance in the SPREE gas measurement on the thickness of doped tin oxide over coatings
    Fischer, D. and Hertwig, A. and Beck, U. and Negendank, D. and Lohse, V. and Kormunda, M. and Esser, N.
    Applied Surface Science 421 480-486 (2017)
    In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29-56. nm, the second was iron doped on gold/glass substrate with 1.6-6.3. nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6. nm to 5.1. nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3. nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much. © 2016.
    view abstractdoi: 10.1016/j.apsusc.2016.11.188
  • 2017 • 183 Characterization of anisotropically shaped silver nanoparticle arrays via spectroscopic ellipsometry supported by numerical optical modeling
    Gkogkou, D. and Shaykhutdinov, T. and Oates, T.W.H. and Gernert, U. and Schreiber, B. and Facsko, S. and Hildebrandt, P. and Weidinger, I.M. and Esser, N. and Hinrichs, K.
    Applied Surface Science 421 460-464 (2017)
    The present investigation aims to study the optical response of anisotropic Ag nanoparticle arrays deposited on rippled silicon substrates by performing a qualitative comparison between experimental and theoretical results. Spectroscopic ellipsometry was used along with numerical calculations using finite-difference time-domain (FDTD) method and rigorous coupled wave analysis (RCWA) to reveal trends in the optical and geometrical properties of the nanoparticle array. Ellipsometric data show two resonances, in the orthogonal x and y directions, that originate from localized plasmon resonances as demonstrated by the calculated near-fields from FDTD calculations. The far-field calculations by RCWA point to decoupled resonances in x direction and possible coupling effects in y direction, corresponding to the short and long axis of the anisotropic nanoparticles, respectively. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2016.10.105
  • 2017 • 182 Efficient Gene Transfection through Inhibition of β-Sheet (Amyloid Fiber) Formation of a Short Amphiphilic Peptide by Gold Nanoparticles
    Jana, P. and Samanta, K. and Bäcker, S. and Zellermann, E. and Knauer, S. and Schmuck, C.
    Angewandte Chemie - International Edition (2017)
    The effect of citrate-stabilized gold nanoparticles (AuNPs) on the secondary structure of an artificial β-sheet-forming cationic peptide has been studied. The AuNPs inhibited β-sheet formation and led to fragmented fibrils and spherical oligomers with assembled AuNPs on their surface. Besides this structural change, the functional properties of the peptide are also different. Whereas the peptide was unable to act as a vector for gene delivery, formation of a complex with AuNPs allowed successful gene delivery into cells. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201700713
  • 2017 • 181 Colloidal Stability and Surface Chemistry Are Key Factors for the Composition of the Protein Corona of Inorganic Gold Nanoparticles
    Johnston, B.D. and Kreyling, W.G. and Pfeiffer, C. and Schäffler, M. and Sarioglu, H. and Ristig, S. and Hirn, S. and Haberl, N. and Thalhammer, S. and Hauck, S.M. and Semmler-Behnke, M. and Epple, M. and Hühn, J. and Del Pino, ...
    Advanced Functional Materials 27 (2017)
    To study the influence of colloidal stability on protein corona formation, gold nanoparticles are synthesized with five distinct surface modifications: coating with citric acid, bis(p-sulfonatophenyl)phenylphosphine dihydrate dipotassium salt, thiol-terminated methoxy-polyethylene glycol, dodecylamine-grafted poly(isobutylene-alt-maleic anhydride), and dodecylamine-grafted poly(isobutylene-alt-maleic anhydride) conjugated with polyethylene glycol. The nanoparticles are incubated with serum or bronchoalveolar lavage fluid from C57BL/6 mice (15 min or 24 h) to assess the effect of differential nanoparticle surface presentation on protein corona formation in the air–blood barrier exposure pathway. Proteomic quantification and nanoparticle size measurements are used to assess protein corona formation. We show that surface modification has a clear effect on the size and the composition of the protein corona that is related to the colloidal stability of the studied nanoparticles. Additionally, differences in the composition and size of the protein corona are shown between biological media and duration of exposure, indicating evolution of the corona through this exposure pathway. Consequently, a major determinant of protein corona formation is the colloidal stability of nanoparticles in biological media and chemical or environmental modification of the nanoparticles alters the surface presentation of the functional epitope in vivo. Therefore, the colloidal stability of nanoparticles has a decisive influence on nano–bio interactions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201701956
  • 2017 • 180 Optimizing inVitro Impedance and Physico-Chemical Properties of Neural Electrodes by Electrophoretic Deposition of Pt Nanoparticles
    Koenen, S. and Rehbock, C. and Heissler, H.E. and Angelov, S.D. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
    ChemPhysChem 18 1108-1117 (2017)
    Neural electrodes suffer from an undesired incline in impedance when in permanent contact with human tissue. Nanostructures, induced by electrophoretic deposition (EPD) of ligand-free laser-generated nanoparticles (NPs) on the electrodes are known to stabilize impedance invivo. Hence, Pt surfaces were systematically EPD-coated with Pt NPs and evaluated for impedance as well as surface coverage, contact angle, electrochemically active surface area (ECSA) and surface oxidation. The aim was to establish a systematic correlation between EPD process parameters and physical surface properties. The findings clearly reveal a linear decrease in impedance with increasing surface coverage, which goes along with a proportional reduction of the contact angle and an increase in ECSA and surface oxidation. EPD process parameters, prone to yield surface coatings with low impedance, are long deposition times (40-60min), while high colloid concentrations (&gt;250μgmL-1) and electric field strengths (&gt;25Vcm-1) should be avoided due to detrimental NP assemblage effects. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.201601180
  • 2017 • 179 Optimizing in Vitro Impedance and Physico-Chemical Properties of Neural Electrodes by Electrophoretic Deposition of Pt Nanoparticles
    Koenen, S. and Rehbock, C. and Heissler, H.E. and Angelov, S.D. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
    ChemPhysChem 18 1108-1117 (2017)
    Neural electrodes suffer from an undesired incline in impedance when in permanent contact with human tissue. Nanostructures, induced by electrophoretic deposition (EPD) of ligand-free laser-generated nanoparticles (NPs) on the electrodes are known to stabilize impedance in vivo. Hence, Pt surfaces were systematically EPD-coated with Pt NPs and evaluated for impedance as well as surface coverage, contact angle, electrochemically active surface area (ECSA) and surface oxidation. The aim was to establish a systematic correlation between EPD process parameters and physical surface properties. The findings clearly reveal a linear decrease in impedance with increasing surface coverage, which goes along with a proportional reduction of the contact angle and an increase in ECSA and surface oxidation. EPD process parameters, prone to yield surface coatings with low impedance, are long deposition times (40–60 min), while high colloid concentrations (&gt;250 μg mL−1) and electric field strengths (&gt;25 V cm−1) should be avoided due to detrimental NP assemblage effects. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cphc.201601180
  • 2017 • 178 Effect of titania surface modification of mesoporous silica SBA-15 supported Au catalysts: Activity and stability in the CO oxidation reaction
    Kučerová, G. and Strunk, J. and Muhler, M. and Behm, R.J.
    Journal of Catalysis 356 214-228 (2017)
    As part of an ongoing effort to understand the deactivation and improve the stability of metal oxide-supported Au catalysts in the low-temperature CO oxidation reaction while maintaining their high activity, we have investigated the influence of a mesoporous silica SBA-15 substrate on the activity and stability of Au/TiO2 catalysts, which consist of a SBA-15 support surface modified by a monolayer of TiOx with Au nanoparticles on top. The extent of the TiOx surface modification was systematically increased, while the Au loading and the Au particle sizes were largely kept constant. Employing kinetic measurements at three different temperatures (30 °C, 80 °C, 180 °C) and a number of ex situ methods as well as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for catalyst characterization, we found that the activity of these catalysts increases significantly with the Ti concentration and with reaction temperature. The tendency for deactivation remains essentially unchanged. Detailed in situ DRIFTS measurements reveal that the Au nanoparticles are largely formed on the TiOx surface-modified areas of the SBA-15 support and that the tendency for surface carbonate formation is very low. The observed deactivation may at least partly be related to the accumulation of molecularly adsorbed H2O species, in particular at low temperatures (30 °C). These are likely to be formed from surface hydroxyl groups, they may affect the reaction either by blocking of active sites or by blocking the adsorption of reactants on the substrate. Other effects, such as reaction induced changes in the titania layer, must however, play a role as well, both at 80 °C and in particular at 180 °C, where accumulation of adsorbed species is negligible. The mechanistic ideas are supported by reactivation tests subsequent to calcination at 400 °C, which were found to fully restore the initial activity. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcat.2017.09.017
  • 2017 • 177 Direct Integration of Laser-Generated Nanoparticles into Transparent Nail Polish: The Plasmonic "goldfinger"
    Lau, M. and Waag, F. and Barcikowski, S.
    Industrial and Engineering Chemistry Research 56 3291-3296 (2017)
    A transparent nail varnish can be colored simply and directly with laser-generated nanoparticles. This does not only enable coloring of the varnish for cosmetic purposes, but also gives direct access to nanodoped varnishes to be used on any solid surface. Therefore, nanoparticle properties such as plasmonic properties or antibacterial effects can be easily adapted to surfaces for medical or optical purposes. The presented method for integration of metal (gold, platinum, silver, and alloy) nanoparticles into varnishes is straightforward and gives access to nanodoped polishes with optical properties, difficult to be achieved by dispersing powder pigments in the high-viscosity liquids. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.iecr.7b00039
  • 2017 • 176 Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence
    Lin, W. and Schmidt, J. and Mahler, M. and Schindler, T. and Unruh, T. and Meyer, B. and Peukert, W. and Segets, D.
    Langmuir 33 13581-13589 (2017)
    We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basis. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.7b03079
  • 2017 • 175 Size- and density-controlled deposition of Ag nanoparticle films by a novel low-temperature spray chemical vapour deposition method—research into mechanism, particle growth and optical simulation
    Liu, Y. and Plate, P. and Hinrichs, V. and Köhler, T. and Song, M. and Manley, P. and Schmid, M. and Bartsch, P. and Fiechter, S. and Lux-Steiner, M.C. and Fischer, C.-H.
    Journal of Nanoparticle Research 19 (2017)
    Ag nanoparticles have attracted interest for plasmonic absorption enhancement of solar cells. For this purpose, well-defined particle sizes and densities as well as very low deposition temperatures are required. Thus, we report here a new spray chemical vapour deposition method for producing Ag NP films with independent size and density control at substrate temperatures even below 100 °C, which is much lower than for many other techniques. This method can be used on different substrates to deposit Ag NP films. It is a reproducible, low-cost process which uses trimethylphosphine (hexafluoroacetylacetonato) silver as a precursor in alcoholic solution. By systematic variation of deposition parameters and classic experiments, mechanisms of particle growth and of deposition processes as well as the low decomposition temperature of the precursor could be explained. Using the 3D finite element method, absorption spectra of selected samples were simulated, which fitted well with the measured results. Hence, further applications of such Ag NP films for generating plasmonic near field can be predicted by the simulation. © 2017, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-017-3834-6
  • 2017 • 174 Enhancement of photocurrent in an ultra-thin perovskite solar cell by Ag nanoparticles deposited at low temperature
    Liu, Y. and Lang, F. and Dittrich, T. and Steigert, A. and Fischer, C.-H. and Köhler, T. and Plate, P. and Rappich, J. and Lux-Steiner, M.Ch. and Schmid, M.
    RSC Advances 7 1206-1214 (2017)
    Ultra-thin perovskite absorber layers have attracted increasing interest since they are suitable for application in semi-transparent perovskite and tandem solar cells. In this study, size and density controlled plasmonic silver nanoparticles are successfully incorporated into ultra-thin perovskite solar cells through a low temperature spray chemical vapor deposition method. Incorporation of Ag nanoparticles leads to a significant enhancement of 22.2% for the average short-circuit current density. This resulted in a relative improvement of 22.5% for the average power conversion efficiency. Characterization by surface photovoltage and photoluminescence provides evidence that the implemented silver nanoparticles can enhance the charge separation and the trapping of electrons into the TiO2 layer at the CH3NH3PbI3/TiO2 interface. The application of these silver nanoparticles therefore has promise to enhance the ultra-thin perovskite solar cells. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/C6RA25149H
  • 2017 • 173 Laser synthesis, structure and chemical properties of colloidal nickel-molybdenum nanoparticles for the substitution of noble metals in heterogeneous catalysis
    Marzun, G. and Levish, A. and Mackert, V. and Kallio, T. and Barcikowski, S. and Wagener, P.
    Journal of Colloid and Interface Science 489 57-67 (2017)
    Platinum and iridium are rare and expensive noble metals that are used as catalysts for different sectors including in heterogeneous chemical automotive emission catalysis and electrochemical energy conversion. Nickel and its alloys are promising materials to substitute noble metals. Nickel based materials are cost-effective with good availability and show comparable catalytic performances. The nickel-molybdenum system is a very interesting alternative to platinum in water electrolysis. We produced ligand-free nickel-molybdenum nanoparticles by laser ablation in water and acetone. Our results show that segregated particles were formed in water due to the oxidation of the metals. X-ray diffraction shows a significant change in the lattice parameter due to a diffusion of molybdenum atoms into the nickel lattice with increasing activity in the electrochemical oxygen evolution reaction. Even though the solubility of molecular oxygen in acetone is higher than in water, there were no oxides and a more homogeneous metal distribution in the particles in acetone as seen by TEM-EDX. This showed that dissolved molecular oxygen does not control oxide formation. Overall, the laser ablation of pressed micro particulate mixtures in liquids offers a combinational synthesis approach that allows the screening of alloy nanoparticles for catalytic testing and can convert micro-mixtures into nano-alloys. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2016.09.014
  • 2017 • 172 Peptide Cross-linkers: Immobilization of Platinum Nanoparticles Highly Dispersed on Graphene Oxide Nanosheets with Enhanced Photocatalytic Activities
    Mizutaru, T. and Marzun, G. and Kohsakowski, S. and Barcikowski, S. and Hong, D. and Kotani, H. and Kojima, T. and Kondo, T. and Nakamura, J. and Yamamoto, Y.
    ACS Applied Materials and Interfaces 9 9996-10002 (2017)
    For exerting potential catalytic and photocatalytic activities of metal nanoparticles (MNPs), immobilization of MNPs on a support medium in highly dispersed state is desired. In this Research Article, we demonstrated that surfactant-free platinum nanoparticles (PtNPs) were efficiently immobilized on graphene oxide (GO) nanosheets in a highly dispersed state by utilizing oligopeptide β-sheets as a cross-linker. The fluorenyl-substituted peptides were designed to form β-sheets, where metal-binding thiol groups and protonated and positively charged amino groups are integrated on the opposite sides of the surface of a β-sheet, which efficiently bridge PtNPs and GO nanosheet. In comparison to PtNP/GO composite without the peptide linker, the PtNP/peptide/GO ternary complex exhibited excellent photocatalytic dye degradation activity via electron transfer from GO to PtNP and simultaneous hole transfer from oxidized GO to the dye. Furthermore, the ternary complex showed photoinduced hydrogen evolution upon visible light irradiation using a hole scavenger. This research provides a new methodology for the development of photocatalytic materials by a bottom-up strategy on the basis of self-assembling features of biomolecules. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b16765
  • 2017 • 171 Probing Oxide Reduction and Phase Transformations at the Au-TiO2 Interface by Vibrational Spectroscopy
    Pougin, A. and Lüken, A. and Klinkhammer, C. and Hiltrop, D. and Kauer, M. and Tölle, K. and Havenith-Newen, M. and Morgenstern, K. and Grünert, W. and Muhler, M. and Strunk, J.
    Topics in Catalysis 60 1744-1753 (2017)
    By a combination of FT-NIR Raman spectroscopy, infrared spectroscopy of CO adsorption under ultrahigh vacuum conditions (UHV-IR) and Raman spectroscopy in the line scanning mode the formation of a reduced titania phase in a commercial Au/TiO2 catalyst and in freshly prepared Au/anatase catalysts was detected. The reduced phase, formed at the Au-TiO2 interface, can serve as nucleation point for the formation of stoichiometric rutile. TinO2n−1 Magnéli phases, structurally resembling the rutile phase, might be involved in this process. The formation of the reduced phase and the rutilization process is clearly linked to the presence of gold nanoparticles and it does not proceed under similar conditions with the pure titania sample. Phase transformations might be both thermally or light induced, however, the colloidal deposition synthesis of the Au/TiO2 catalysts is clearly ruled out as cause for the formation of the reduced phase. © 2017, The Author(s).
    view abstractdoi: 10.1007/s11244-017-0851-8
  • 2017 • 170 Encapsulation of Bimetallic Metal Nanoparticles into Robust Zirconium-Based Metal-Organic Frameworks: Evaluation of the Catalytic Potential for Size-Selective Hydrogenation
    Rösler, C. and Dissegna, S. and Rechac, V.L. and Kauer, M. and Guo, P. and Turner, S. and Ollegott, K. and Kobayashi, H. and Yamamoto, T. and Peeters, D. and Wang, Y. and Matsumura, S. and Van Tendeloo, G. and Kitagawa, H. and Mu...
    Chemistry - A European Journal 23 3583-3594 (2017)
    The realization of metal nanoparticles (NPs) with bimetallic character and distinct composition for specific catalytic applications is an intensively studied field. Due to the synergy between metals, most bimetallic particles exhibit unique properties that are hardly provided by the individual monometallic counterparts. However, as small-sized NPs possess high surface energy, agglomeration during catalytic reactions is favored. Sufficient stabilization can be achieved by confinement of NPs in porous support materials. In this sense, metal-organic frameworks (MOFs) in particular have gained a lot of attention during the last years; however, encapsulation of bimetallic species remains challenging. Herein, the exclusive embedding of preformed core-shell PdPt and RuPt NPs into chemically robust Zr-based MOFs is presented. Microstructural characterization manifests partial retention of the core-shell systems after successful encapsulation without harming the crystallinity of the microporous support. The resulting chemically robust NP@UiO-66 materials exhibit enhanced catalytic activity towards the liquid-phase hydrogenation of nitrobenzene, competitive with commercially used Pt on activated carbon, but with superior size-selectivity for sterically varied substrates. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201603984
  • 2017 • 169 Changes within the stabilizing layer of ZnO nanoparticles upon washing
    Schindler, T. and Schmutzler, T. and Schmiele, M. and Lin, W. and Segets, D. and Peukert, W. and Appavou, M.-S. and Kriele, A. and Gilles, R. and Unruh, T.
    Journal of Colloid and Interface Science 504 356-362 (2017)
    ZnO nanoparticles (NPs) are highly relevant for various industrial applications, however, after synthesis of the NPs residual chemicals need to be removed from the colloidal raw product by washing, as they may influence the performance of the final device. In the present study we focus on the effect of washing by antisolvent flocculation with subsequent redispersion of the NPs on the stabilizing acetate shell. Purification of the ZnO nanoparticles is reported to be optimal with respect to zeta potential that has a maximum after one washing cycle. In this work, we will shed light on this observation using small angle X-ray and neutron scattering (SAXS, SANS) by demonstrating that after the first washing cycle the content of acetate in the ligand shell around the ZnO NPs increases. In detail, it was observed that the diffuse acetate shell shrinks to the size of a monolayer upon washing but the acetate content of this monolayer is higher than within the diffuse shell of the particles of the native dispersion. A second washing cycle reduces the acetate concentration within the stabilizing shell and the stability of the dispersion drops accordingly. After another (third) washing cycle strong agglomeration was observed for all investigated samples. © 2017 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2017.05.059
  • 2017 • 168 Co3O4@Co/NCNT Nanostructure Derived from a Dicyanamide-Based Metal-Organic Framework as an Efficient Bi-functional Electrocatalyst for Oxygen Reduction and Evolution Reactions
    Sikdar, N. and Konkena, B. and Masa, J. and Schuhmann, W. and Maji, T.K.
    Chemistry - A European Journal 23 18049-18056 (2017)
    There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)2(N(CN)2)]⋅(N(CN)2)⋅(5 H2O)}n [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN)2 −=dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H2/Ar atmosphere (at 800 °C) and further mild calcination yielded Co3O4@Co core–shell nanoparticle-encapsulated N-doped carbon nanotubes (Co3O4@Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core–shell Co3O4@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of −1 mA cm−2 and the OER with a potential of 1.61 V at 10 mA cm−2, which is competitive with the most active bi-functional catalysts reported previously. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/chem.201704211
  • 2017 • 167 Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating
    Surmeneva, M.A. and Sharonova, A.A. and Chernousova, S. and Prymak, O. and Loza, K. and Tkachev, M.S. and Shulepov, I.A. and Epple, M. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 156 104-113 (2017)
    A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000 nm thick), silver nanoparticles (second layer; 1.5 μg Ag cm−2) and calcium phosphate (third layer, either 150 or 1000 nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3 days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150 nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2017.05.016
  • 2017 • 166 Adhesion properties of a three-layer system based on RF-magnetron sputter deposited calcium-phosphate coating and silver nanoparticles
    Tkachev, M.S. and Melnikov, E.S. and Surmeneva, M.A. and Sharonova, A.A. and Surmenev, R.A. and Korneva, O.S. and Shulepov, I.A. and Loza, K. and Epple, M.
    Proceedings of the 11th International Forum on Strategic Technology, IFOST 2016 88-90 (2017)
    A three-layer system of hydroxyapatite (HA) coating - Ag nanoparticles - HA coating with an overall thickness of 1.2 μm was prepared. The radio-frequency (RF) magnetron sputtering was used to prepare the first layer of hydroxyapatite coating on titanium. Then electrophoretic deposition of silver nanoparticles on the prepared HA layer was done followed by deposition of the second layer of HA by RFmagnetron sputtering. The adhesion strength was investigated by the scratch test method. Scanning electron microscopy and optical microscopy allowed to qualitatively estimate the deformation mechanisms of the biocomposites after the scratch test. © 2016 IEEE.
    view abstractdoi: 10.1109/IFOST.2016.7884197
  • 2017 • 165 Nanoparticulate versus ionic silver: Behavior in the tank water, bioaccumulation, elimination and subcellular distribution in the freshwater mussel Dreissena polymorpha
    Zimmermann, S. and Ruchter, N. and Loza, K. and Epple, M. and Sures, B.
    Environmental Pollution 222 251-260 (2017)
    Zebra mussels (Dreissena polymorpha) were exposed to polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP; hydrodynamic diameter 80 nm; solid diameter 50 nm) to investigate the behavior of Ag in the tank water with respect to its uptake, bioaccumulation, elimination and subcellular distribution in the mussel soft tissue. Parallel experiments were performed with ionic Ag (AgNO3) to unravel possible differences between the metal forms. The recovery of the applied Ag concentration (500 μg/L) in the tank water was clearly affected by the metal source (AgNP < AgNO3) and water type (reconstituted water < tap water). Filtration (< 0.45 μm) of water samples showed different effects on the quantified metal concentration depending on the water type and Ag form. Ag accumulation in the mussel soft tissue was neither influenced by the metal source nor by the water type. Ag concentrations in the mussel soft tissue did not decrease during 14 days of depuration. For both metal forms the Ag distribution within different subcellular fractions, i.e. metal-rich granules (MRG), cellular debris, organelles, heat-sensitive proteins (HSP) and metallothionein-like proteins (MTLP), revealed time-dependent changes which can be referred to intracellular Ag translocation processes. The results provide clear evidence for the uptake of Ag by the mussel soft tissue in nanoparticulate as well as in ionic form. Thus, zebra mussels could be used as effective accumulation indicators for environmental monitoring of both Ag forms. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.envpol.2016.12.048
  • 2017 • 164 Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane
    Zirehpour, A. and Rahimpour, A. and Ulbricht, M.
    Journal of Membrane Science 531 59-67 (2017)
    In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2017.02.049
  • 2017 • 163 High surface area, amorphous titania with reactive Ti3+ through a photo-assisted synthesis method for photocatalytic H2 generation
    Zywitzki, D. and Jing, H. and Tüysüz, H. and Chan, C.K.
    Journal of Materials Chemistry A 5 10957-10967 (2017)
    Amorphous titania-based photocatalysts are synthesized using a facile, UV-light mediated method and evaluated as photocatalysts for hydrogen evolution from water/methanol mixtures. The photocatalysts are prepared through the direct injection of a titanium alkoxide precursor into a water/methanol mixture, with subsequent hydrolysis, condensation, and polycondensation to form TiOx(OH)y species under UV-irradiation. The resulting amorphous titania materials exhibit an overall higher hydrogen evolution rate compared to a crystalline TiO2 reference (P25) on a molar basis of the photocatalyst due to their highly porous structure and high surface area (∼500 m2 g-1). The employed titanium alkoxide precursor did not play a major role in affecting the hydrogen evolution rate or the catalyst surface and morphology. A blue coloration, which is associated with the formation of Ti3+ species, was observed in the amorphous titania but not in P25 upon light irradiation and is enabled by the porous and disordered structure of the amorphous photocatalyst. The Ti3+ species are also used to reduce protons to H2 in the absence of light irradiation or reduce Pt2+ to form Pt nanoparticles. These Pt nanoparticles are smaller and better dispersed on the photocatalyst compared to particles prepared using conventional photodeposition, leading to higher H2 evolution rates. The results show that the direct injection method is a facile approach for the preparation of high surface area titania photocatalysts containing Ti3+ species with good photocatalytic activity for the production of H2. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7ta01614j
  • 2016 • 162 Co@Co3O4 Encapsulated in Carbon Nanotube-Grafted Nitrogen-Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode
    Aijaz, A. and Masa, J. and Rösler, C. and Xia, W. and Weide, P. and Botz, A.J.R. and Fischer, R.A. and Schuhmann, W. and Muhler, M.
    Angewandte Chemie - International Edition 55 4087-4091 (2016)
    Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal-air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core-shell Co@Co3O4 nanoparticles embedded in CNT-grafted N-doped carbon-polyhedra obtained by the pyrolysis of cobalt metal-organic framework (ZIF-67) in a reductive H2 atmosphere and subsequent controlled oxidative calcination. The catalysts afford 0.85 V reversible overvoltage in 0.1 m KOH, surpassing Pt/C, IrO2, and RuO2 and thus ranking them among one of the best non-precious-metal electrocatalysts for reversible oxygen electrodes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201509382
  • 2016 • 161 Ultrafiltration membrane-based purification of bioconjugated gold nanoparticle dispersions
    Alele, N. and Streubel, R. and Gamrad, L. and Barcikowski, S. and Ulbricht, M.
    Separation and Purification Technology 157 120-130 (2016)
    Functionalization of nanoparticles (NP) with biomolecules to form bioconjugated systems has received large attention in biomedical applications. However, purification of these nanoparticle bioconjugates from unbound free biofunctional ligands (e.g., peptides) remains a significant challenge in the production of well-defined materials. The conventional separation methods often compromise the product's properties and recovery. In this work, removal of excess of unbound peptides after the bioconjugation step to yield functionalized gold nanoparticles (AuNP) was achieved by exploiting the sieving properties of commercial regenerated cellulose (RC) ultrafiltration (UF) membranes. The RC membrane with nominal molecular weight cut-off (NMWCO) of 30 kDa precisely fractionated the mixtures and purified gold nanoparticle-peptide bioconjugates in a pressure driven semi-continuous diafiltration process. The RC 30 kDa membrane showed absolute rejection of the bioconjugated AuNP and the recovery of AuNP-peptide bioconjugate in the retentate was >87% relative to the initial amount in the mixture. In addition, the separation efficiency and throughput results were much better compared to the centrifugal membrane filtration method using an analogous membrane. All results indicate that by choice of an appropriate membrane type and barrier pore size, and with optimized solution chemistry and filtration parameters, ultrafiltration membranes, and in particular RC membranes, can be very well suited for the purification of bioconjugated nanoparticle dispersions, and the diafiltration mode is very well suited for upscaling. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.seppur.2015.11.033
  • 2016 • 160 Laser-based in situ embedding of metal nanoparticles into bioextruded alginate hydrogel tubes enhances human endothelial cell adhesion
    Blaeser, A. and Million, N. and Campos, D.F.D. and Gamrad, L. and Köpf, M. and Rehbock, C. and Nachev, M. and Sures, B. and Barcikowski, S. and Fischer, H.
    Nano Research 9 3407-3427 (2016)
    Alginate is a widely used hydrogel in tissue engineering owing to its simple and non-cytotoxic gelation process, ease of use, and abundance. However, unlike hydrogels derived from mammalian sources such as collagen, alginate does not contain cell adhesion ligands. Here, we present a novel laser ablation technique for the in situ embedding of gold and iron nanoparticles into hydrogels. We hypothesized that integration of metal nanoparticles in alginate could serve as an alternative material because of its chemical biofunctionalization ability (coupling of RGD ligands) to favor cell adhesion. Cytocompatibility and biofunctionality of the gels were assessed by cell culture experiments using fibroblasts and endothelial cells. Nanoparticles with an average particle size of 3 nm (gold) and 6 nm (iron) were generated and stably maintained in alginate for up to 6 months. Using an extrusion system, several centimeter-long alginate tubes with an outer diameter of approximately 3 mm and a wall thickness of approximately 150 μm were manufactured. Confocal microscopy revealed homogeneously distributed nanoparticle agglomerates over the entire tube volume. Endothelial cells seeded on iron-loaded gels showed significantly higher viability and an increased degree of spreading, and the number of attached cells was also elevated in comparison to the control and gold-loaded alginates. We conclude that laser-based in situ integration of iron nanoparticles (&le; 0.01 wt.%) in alginate is a straightforward method to generate composite materials that favor the adhesion of endothelial cells. In addition, we show that nanoparticle integration does not impair the alginate’s gelation and 3D biofabrication properties. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s12274-016-1218-3
  • 2016 • 159 Detection of individual nanoparticle impacts using etched carbon nanoelectrodes
    Clausmeyer, J. and Wilde, P. and Löffler, T. and Ventosa, E. and Tschulik, K. and Schuhmann, W.
    Electrochemistry Communications 73 67-70 (2016)
    A rapid and reliable nanofabrication route produces electrodes with beneficial properties for electrochemistry based on stochastic nanoparticle collision events. Carbon nanoelectrodes are etched to expose conical carbon tips which present an increased surface area for the detection of nanoparticle impacts. The tuneable electrode size as well as the conical geometry allow to increase the observed particle impact frequency while maintaining low background noise. Moreover, anodic particle coulometry for the sizing of silver nanoparticles shows that the detected impacts are representative of the polydisperse particle population. © 2016
    view abstractdoi: 10.1016/j.elecom.2016.11.003
  • 2016 • 158 Preformed 2 nm Ag Clusters Deposited into Ionic Liquids: Stabilization by Cation-Cluster Interaction
    Engemann, D.C. and Roese, S. and Hövel, H.
    Journal of Physical Chemistry C 120 6239-6245 (2016)
    Recently, the formation of nanoparticles by sputter deposition of metal atoms onto the surface of room-temperature ionic liquids (RTIL) was reported; however, the growth and stabilization mechanism within the ionic liquid are still in discussion. Here, we present another approach by depositing Ag clusters with a diameter of 2 nm preformed in a supersonic nozzle expansion into an ionic liquid. Thus, the properties and size distribution of the clusters are well-known before deposition. The mixture of the clusters with the ionic liquid is investigated in situ and ex situ with UV/vis measurements and X-ray absorption near-edge structure (XANES) spectroscopy at the Ag L2 edge. The plasmon resonances of the Ag clusters show that up to 10 μg/mL, the clusters stay separated in the RTIL and suggest an interaction process between the cations in the liquid and the surfaces of the clusters, which is confirmed by a shift of the absorption edge in the XANES measurements. For higher cluster concentration and on a longer time scale, the stabilization ability of ionic liquids can be investigated. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b12120
  • 2016 • 157 Gold on Different Manganese Oxides: Ultra-Low-Temperature CO Oxidation over Colloidal Gold Supported on Bulk-MnO2 Nanomaterials
    Gu, D. and Tseng, J.-C. and Weidenthaler, C. and Bongard, H.-J. and Spliethoff, B. and Schmidt, W. and Soulimani, F. and Weckhuysen, B.M. and Schüth, F.
    Journal of the American Chemical Society 138 9572-9580 (2016)
    Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nanosized gold particles (2-3 nm) were supported on α-MnO2 nanowires and mesoporous β-MnO2 nanowire arrays. The materials were extremely active at very low temperature (-80 °C) and also highly stable at 25 °C (70 h) under normal conditions for CO oxidation. The specific reaction rate of 2.8 molCO·h-1·gAu -1 at a temperature as low as -85 °C is almost 30 times higher than that of the most active Au/Mn2O3 catalyst. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/jacs.6b04251
  • 2016 • 156 Improved photoelectrochemical performance of electrodeposited metal-doped BiVO4 on Pt-nanoparticle modified FTO surfaces
    Gutkowski, R. and Peeters, D. and Schuhmann, W.
    Journal of Materials Chemistry A 4 7875-7882 (2016)
    The recombination of photogenerated electron-hole pairs is one of the main limiting factors of photoelectrocatalysts absorbing in the visible part of the solar spectrum. Especially for BiVO4 the slow electron transport to the back contact facilitates charge recombination. Hence, thin layers have to be used to obtain higher photocurrents which are concomitantly only allow low absorption of the incident light. To address this limitation we have modified FTO substrates with Pt-nanoparticles before electrodepositing BiVO4. The Pt-nanoparticles decrease the overpotential for the electrodeposition of BiVO4, but more importantly they provide the basis for decreased charge recombination. Electrodeposited Mo-doped BiVO4 on Pt-nanoparticle modified FTO exhibits a substantially decreased recombination of photogenerated charge carriers during frontside illumination. Simultaneous co-doping of BiVO4 with two different metals leads to a substantial enhancement of the incident-photon-to-current efficiency (IPCE) during light driven oxygen evolution reaction. Highest IPCE (&gt;30% at 1.2 V vs. RHE) values were obtained for Mo/Zn- and Mo/B-doped BiVO4. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ta01340f
  • 2016 • 155 On the Crystallography of Silver Nanoparticles with Different Shapes
    Helmlinger, J. and Prymak, O. and Loza, K. and Gocyla, M. and Heggen, M. and Epple, M.
    Crystal Growth and Design 16 3677-3687 (2016)
    The crystallographic properties of silver nanoparticles with different morphologies (two different kinds of spheres, cubes, platelets, and rods) were derived from X-ray powder diffraction and electron microscopy. The size of the metallic particle core was determined by scanning electron microscopy, and the colloidal stability and the hydrodynamic particle diameter were analyzed by dynamic light scattering. The preferred crystallographic orientation (texture) as obtained by X-ray powder diffraction, including pole figure analysis, and high resolution transmission electron microscopy showed the crystallographic nature of the spheres (almost no texture), the cubes (terminated by {100} faces), the platelets (terminated by {111} faces), and the rods (grown from pentagonal twins along [110] and terminated by {100} faces). The crystallite size was determined by Rietveld refinement of X-ray powder diffraction data and agreed well with the transmission electron microscopic data. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.6b00178
  • 2016 • 154 Silver nanoparticles with different size and shape: Equal cytotoxicity, but different antibacterial effects
    Helmlinger, J. and Sengstock, C. and Groß-Heitfeld, C. and Mayer, C. and Schildhauer, T.A. and Köller, M. and Epple, M.
    RSC Advances 6 18490-18501 (2016)
    The influence of silver nanoparticle morphology on the dissolution kinetics in ultrapure water as well as the biological effect on eukaryotic and prokaryotic cells was examined. Silver nanoparticles with different shapes but comparable size and identical surface functionalisation were prepared, i.e. spheres (diameter 40-80 and 120-180 nm; two different samples), platelets (20-60 nm), cubes (140-180 nm), and rods (diameter 80-120 nm, length &gt; 1000 nm). All particles were purified by ultracentrifugation and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Their colloidal dispersion in ultrapure water and cell culture medium was demonstrated by dynamic light scattering. Size, shape, and colloidal stability were analysed by scanning electron microscopy, atomic force microscopy, dynamic light scattering, and differential centrifugal sedimentation. The dissolution in ultrapure water was proportional to the specific surface area of the silver nanoparticles. The averaged release rate for all particle morphologies was 30 ± 13 ng s-1 m-2 in ultrapure water (T = 25 ± 1°C; pH 4.8; oxygen saturation 93%), i.e. about 10-20 times larger than the release of silver from a macroscopic silver bar (1 oz), possibly due to the presence of surface defects in the nanoparticulate state. All particles were taken up by human mesenchymal stem cells and were cytotoxic in concentrations of &gt;12.5 μg mL-1, but there was no significant influence of the particle shape on the cytotoxicity towards the cells. Contrary to that, the toxicity towards bacteria increased with a higher dissolution rate, suggesting that the toxic species against bacteria are dissolved silver ions. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5ra27836h
  • 2016 • 153 Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study
    Jendrzej, S. and Gökce, B. and Amendola, V. and Barcikowski, S.
    Journal of Colloid and Interface Science 463 299-307 (2016)
    Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50 days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1. day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. © 2015.
    view abstractdoi: 10.1016/j.jcis.2015.10.032
  • 2016 • 152 Plasmon assisted 3D microstructuring of gold nanoparticle-doped polymers
    Jonušauskas, L. and Lau, M. and Gruber, P. and Gökce, B. and Barcikowski, S. and Malinauskas, M. and Ovsianikov, A.
    Nanotechnology 27 (2016)
    3D laser lithography of a negative photopolymer (zirconium/silicon hybrid solgel SZ2080) doped with gold nanoparticles (Au NPs) is performed with a 515 nm and 300 fs laser system and the effect of doping is explored. By varying the laser-generated Au NP doping concentration from 4.8 • 10-6 wt% to 9.8 • 10-3 wt% we find that the fabricated line widths are enlarged by up to 14.8% compared to structures achieved in pure SZ2080. While implicating a positive effect on the photosensitivity, the doping has no adverse impact on the mechanical quality of intricate 3D microstructures produced from the doped nanocompound. Additionally, we found that SZ2080 increases the long term (∼months) colloidal stability of Au NPs in isopropanol. By discussing the nanoparticle-light interaction in the 3D polymer structures we provide implications that our findings might have on other fields, such as biomedicine and photonics. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/15/154001
  • 2016 • 151 Metal-semiconductor pair nanoparticles by a physical route based on bipolar mixing
    Kala, S. and Theissmann, R. and Rouenhoff, M. and Kruis, F.E.
    Nanotechnology 27 (2016)
    In this report a methodology is described and demonstrated for preparing Au-Ge pair nanoparticles with known compositions by extending and modifying the basic steps normally used to synthesize nanoparticles in carrier gas. For the formation of pair nanoparticles by bipolar mixing, two oppositely charged aerosols of nanoparticles having the desired size are produced with the help of two differential mobility analyzers. Then both are allowed to pass through a tube, which provides sufficient residence time to result in nanoparticle pair formation due to Brownian collisions influenced by Coulomb forces. The effect of residence time on the formation of nanoparticle pairs as well as the influence of diffusion and discharging is described. Subsequently, necessary modifications to the experimental setup are demonstrated systematically. The kinetics of nanoparticles pair formation in a carrier gas is also calculated and compared with measurements made with the help of an online aerosol size analysis technique. This synthesis of nanoparticle pairs can be seen as a possible route towards Janus-type nanoparticles. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/12/125604
  • 2016 • 150 Influence of the liquid on femtosecond laser ablation of iron
    Kanitz, A. and Hoppius, J.S. and Gurevich, E.L. and Ostendorf, A.
    Physics Procedia 83 114-122 (2016)
    Ultrashort pulse laser ablation has become a very important industrial method for highly precise material removal ranging from sensitive thin film processing to drilling and cutting of metals. Over the last decade, a new method to produce pure nanoparticles emerged from this technique: Pulsed Laser Ablation in Liquids (PLAL). By this method, the ablation of material by a laser beam is used to generate a metal vapor within the liquid in order to obtain nanoparticles from its recondensation process. It is well known that the liquid significantly alters the ablation properties of the substrate, in our case iron. For example, the ablation rate and crater morphology differ depending on the used liquid. We present our studies on the efficiency and quality of ablated grooves in water, methanol, acetone, ethanol and toluene. The produced grooves are investigated by means of white-light interferometry, EDX and SEM. © 2016 The Authors.
    view abstractdoi: 10.1016/j.phpro.2016.08.022
  • 2016 • 149 Optical and electron microscopy study of laser-based intracellular molecule delivery using peptide-conjugated photodispersible gold nanoparticle agglomerates
    Krawinkel, J. and Richter, U. and Torres-Mapa, M.L. and Westermann, M. and Gamrad, L. and Rehbock, C. and Barcikowski, S. and Heisterkamp, A.
    Journal of Nanobiotechnology 14 (2016)
    Background: Cell-penetrating peptides (CPPs) can act as carriers for therapeutic molecules such as drugs and genetic constructs for medical applications. The triggered release of the molecule into the cytoplasm can be crucial to its effective delivery. Hence, we implemented and characterized laser interaction with defined gold nanoparticle agglomerates conjugated to CPPs which enables efficient endosomal rupture and intracellular release of molecules transported. Results: Gold nanoparticles generated by pulsed laser ablation in liquid were conjugated with CPPs forming agglomerates and the intracellular release of molecules was triggered via pulsed laser irradiation (λ = 532 nm, τpulse = 1 ns). The CPPs enhance the uptake of the agglomerates along with the cargo which can be co-incubated with the agglomerates. The interaction of incident laser light with gold nanoparticle agglomerates leads to heat deposition and field enhancement in the vicinity of the particles. This highly precise effect deagglomerates the nanoparticles and disrupts the enclosing endosomal membrane. Transmission electron microscopy images confirmed this rupture for radiant exposures of 25 mJ/cm2 and above. Successful intracellular release was shown using the fluorescent dye calcein. For a radiant exposure of 35 mJ/cm2 we found calcein delivery in 81 % of the treated cells while maintaining a high percentage of cell viability. Furthermore, cell proliferation and metabolic activity were not reduced 72 h after the treatment. Conclusion: CPPs trigger the uptake of the gold nanoparticle agglomerates via endocytosis and co-resident molecules in the endosomes are released by applying laser irradiation, preventing their intraendosomal degradation. Due to the highly localized effect, the cell membrane integrity is not affected. Therefore, this technique can be an efficient tool for spatially and temporally confined intracellular release. The utilization of specifically designed photodispersible gold nanoparticle agglomerates (65 nm) can open novel avenues in imaging and molecule delivery. Due to the induced deagglomeration the primary, small particles (~5 nm) are more likely to be removed from the body. © 2016 Krawinkel et al.
    view abstractdoi: 10.1186/s12951-015-0155-8
  • 2016 • 148 Few-layer graphene modified with nitrogen-rich metallo-macrocyclic complexes as precursor for bifunctional oxygen electrocatalysts
    Morales, D.M. and Masa, J. and Andronescu, C. and Kayran, Y.U. and Sun, Z. and Schuhmann, W.
    Electrochimica Acta 222 1191-1199 (2016)
    We propose a method for the formation of highly active bifunctional oxygen electrocatalysts, by exploiting the unique features of nitrogen-rich metallo-macrocyclic complexes and the structural and electronic properties of few-layer graphene. The precursors of the electrocatalysts were synthesized by sonication of graphite in DMF leading to exfoliation and the formation of few-layer graphene sheets in the presence of a suitable transition metal macrocyclic complex. After pyrolysis and subsequent mild calcination metal oxide nanoparticles as well as metal-nitrogen (MNx) moieties embedded within a N-doped graphitic carbon matrix are obtained. The formation, in-depth characterization and electrochemical performance of two different catalysts derived from Co and Ni containing precursor complexes are demonstrated. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2016.11.092
  • 2016 • 147 High temperature stability study of carbon supported high surface area catalysts—Expanding the boundaries of ex-situ diagnostics
    Polymeros, G. and Baldizzone, C. and Geiger, S. and Grote, J.P. and Knossalla, J. and Mezzavilla, S. and Keeley, G.P. and Cherevko, S. and Zeradjanin, A.R. and Schüth, F. and Mayrhofer, K.J.J.
    Electrochimica Acta 211 744-753 (2016)
    The performance of proton-exchange membrane fuel cells (PEMFCs) is defined by the equally important parameters of the intrinsic activity and stability of the electrocatalysts. This work focuses on the stability of carbon supported high surface area oxygen reduction reaction catalysts at potentials and temperatures similar to the operating conditions of PEMFCs. The catalysts used for this investigation consist of Pt nanoparticles of the same particle size supported on two types of carbon support having different textural properties, i.e., Vulcan and Hollow Graphitic Spheres (HGS). A broad toolbox of characterization techniques is utilized at 60 °C in order to resolve the contribution of the different degradation mechanisms, namely nanoparticle coalescence, metal dissolution and the corrosion of carbon support, to the total active surface area loss. The results obtained by investigating the impact of temperature, potential treatment and catalyst layer morphology on the aging behavior lead to a deeper understanding of the aging mechanisms and their interrelation at application-relevant conditions. Moreover, the previously reported improved performance of the Pt/HGS catalyst is confirmed also under higher temperatures. The experimental approach introduced in this work, highlights new challenges for high-temperature degradation investigations with supported PEMFC catalyst. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.electacta.2016.06.105
  • 2016 • 146 Hollow Zn/Co Zeolitic Imidazolate Framework (ZIF) and Yolk-Shell Metal@Zn/Co ZIF Nanostructures
    Rösler, C. and Aijaz, A. and Turner, S. and Filippousi, M. and Shahabi, A. and Xia, W. and Van Tendeloo, G. and Muhler, M. and Fischer, R.A.
    Chemistry - A European Journal 22 3304-3311 (2016)
    Metal-organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well-defined hollow Zn/Co-based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn-MOF (ZIF-8) on preformed Co-MOF (ZIF-67) nanocrystals that involve in situ self-sacrifice/excavation of the Co-MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co-ZIF shells to generate yolk-shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co-ZIF with dominance of the Zn-MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201503619
  • 2016 • 145 Influence of the degree of infiltration of modified activated carbons with CuO/ZnO on the separation of NO2 at ambient temperatures
    Sager, U. and Däuber, E. and Bathen, D. and Asbach, C. and Schmidt, F. and Tseng, J.-C. and Pommerin, A. and Weidenthaler, C. and Schmidt, W.
    Adsorption Science and Technology 34 307-319 (2016)
    The reduction of NO2 in air at ambient temperatures with activated carbons can be increased by the infiltration of metal oxide nanoparticles into the sorbents. The NO2 is first adsorbed to the activated carbon and subsequently catalytically reduced to physiologically neutral substances by the metal oxides. The catalytic reduction at ambient temperatures is rather slow. In a former study concerning the application in cabin air filters, it was shown that the modification of activated carbon with 5 wt% CuO/ZnO leads to reduced breakthrough of NO2 and that the adsorbent was able to regenerate between repeated NO2 adsorption cycles. Here we show that the efficiency of the sorbent can be more than doubled by increasing the metal oxide infiltration to 20 wt% whereas a further increase in loading yields no additional improvement, due to a partial transformation of the oxidic compounds. © 2016, © The Author(s) 2016.
    view abstractdoi: 10.1177/0263617416653120
  • 2016 • 144 Silicon-based nanocomposites for thermoelectric application
    Schierning, G. and Stoetzel, J. and Chavez, R. and Kessler, V. and Hall, J. and Schmechel, R. and Schneider, T. and Petermann, N. and Wiggers, H. and Angst, S. and Wolf, D.E. and Stoib, B. and Greppmair, A. and Stutzmann, M. and B...
    Physica Status Solidi (A) Applications and Materials Science 213 497-514 (2016)
    Here we present the realization of efficient and sustainable silicon-based thermoelectric materials from nanoparticles. We employ a gas phase synthesis for the nanoparticles which is capable of producing doped silicon (Si) nanoparticles, doped alloy nanoparticles of silicon and germanium (Ge), SixGe1-x, and doped composites of Si nanoparticles with embedded metal silicide precipitation phases. Hence, the so-called "nanoparticle in alloy" approach, theoretically proposed in the literature, forms a guideline for the material development. For bulk samples, a current-activated pressure-assisted densification process of the nanoparticles was optimized in order to obtain the desired microstructure. For thin films, a laser annealing process was developed. Thermoelectric transport properties were characterized on nanocrystalline bulk samples and laser-sintered-thin films. Devices were produced from nanocrystalline bulk silicon in the form of p-n junction thermoelectric generators, and their electrical output data were measured up to hot side temperatures of 750°C. In order to get a deeper insight into thermoelectric properties and structure forming processes, a 3D-Onsager network model was developed. This model was extended further to study the p-n junction thermoelectric generator and understand the fundamental working principle of this novel device architecture. Gas phase synthesis of composite nanoparticles; nanocrystalline bulk with optimized composite microstructure; laser-annealed thin film. The authors fabricated thermoelectric nanomaterials from doped silicon and silicon and germanium alloy nanoparticles, as well as composites of Si nanoparticles with embedded metal silicide nanoparticles. Processing was performed applying a current-activated pressure-assisted densification process for bulk samples and a laser annealing process for thin film samples. Devices were produced in the form of pn junction thermoelectric generators. A 3D-Onsager network model was used to understand the fundamental working principle of this novel device architecture. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201532602
  • 2016 • 143 Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): Effect of thermal treatments and influence of substrate and particle size
    Schilling, M. and Ziemann, P. and Zhang, Z. and Biskupek, J. and Kaiser, U. and Wiedwald, U.
    Beilstein Journal of Nanotechnology 7 591-604 (2016)
    Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: "small" NPs with diameters in the range of 2-3 nm and "large" ones in the range of 5-8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600-650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min. © 2016 Schilling et al.
    view abstractdoi: 10.3762/bjnano.7.52
  • 2016 • 142 Nanoparticles for light management in ultrathin chalcopyrite solar cells
    Schmid, M. and Manley, P. and Ott, A. and Song, M. and Yin, G.
    Journal of Materials Research 31 3273-3289 (2016)
    We evaluate the potential of inserting metallic, metal-dielectric core-shell, and fully dielectric nanoparticles in ultrathin chalcopyrite solar cells to enhance absorption which experiences a significant drop for absorber thicknesses below 500 nm. For different integration positions at the front or at the rear of the solar cell structure theoretical expectations and potential benefits originating from light scattering, near-field enhancement and coupling into waveguide modes by the nanoparticles are presented. These benefits are always balanced against experimental challenges arising for particular geometries due to the very specific fabrication processes of chalcopyrite solar cells. In particular high absorber deposition temperatures as well as contact layers that are relatively thick compared to other devices need to be considered. Based on this, we will need to go beyond some geometries that have proven beneficial for other types of solar cells and identify the most promising configurations for chalcopyrite-based devices. © 2016 Materials Research Society.
    view abstractdoi: 10.1557/jmr.2016.382
  • 2016 • 141 Conjugation of thiol-terminated molecules to ultrasmall 2 nm-gold nanoparticles leads to remarkably complex 1H-NMR spectra
    Schuetze, B. and Mayer, C. and Loza, K. and Gocyla, M. and Heggen, M. and Epple, M.
    Journal of Materials Chemistry B 4 2179-2189 (2016)
    Gold nanoparticles, functionalized by aliphatic and aromatic mercapto-functionalized carboxylic acids and by two small peptides (CG and CGGRGD), respectively, were synthesized by the reduction of HAuCl4 with NaBH4 in the presence of the above ligands. After purification by centrifugation or filtration and redispersion, the dispersed nanoparticles were analysed by differential centrifugal sedimentation (DCS), high-resolution transmission electron microscopy (HRTEM), and a variety of NMR spectroscopic techniques: 1H-NMR, 1H,1H-COSY and 1H-DOSY. The hydrodynamic diameter of the particles was between 1.8 and 4.4 nm, as determined by DOSY, in good agreement with the DCS and HRTEM results. Diffusion ordered spectroscopy (DOSY) turned out to be a valuable and non-destructive tool to determine the hydrodynamic diameter of dispersed nanoparticles and to control the purity of the final particles. The coordination of the organic molecules to the gold nanoparticles resulted in distinct and complex changes in the 1H-NMR spectra. These were only partially explainable but clearly caused by the vicinity of the molecules to the gold nanoparticle. © The Royal Society of Chemistry 2016.
    view abstractdoi: 10.1039/c5tb02443a
  • 2016 • 140 A novel magnetically-separable porous iron-oxide nanocomposite as an adsorbent for methylene blue (MB) dye
    Sehlleier, Y.H. and Hardt, S. and Schulz, C. and Wiggers, H.
    Journal of Environmental Chemical Engineering 4 3779-3787 (2016)
    In this study, efficient and magnetically separable adsorbents for the removal of organic pollutants from water are developed, which are both, environmental friendly and cheap to produce. A new type of porous iron-oxide/polymer nanocomposite was synthesized by a two-step process utilizing surface modification of gas-phase synthesized iron-oxide nanoparticles and a subsequent polymerization process. The potential of iron-oxide/polymer composite adsorbents with a large surface area for the removal of organic components was studied using methylene blue (MB) as a test substance. Adsorption isotherms fitted well with the Langmuir isotherm model and the adsorption capacity of MB on this adsorbent was found to be as high as 298 mg/g which is several times higher than the adsorption capacity of a number of recently reported potential adsorbents. Owing to its magnetic properties, the polluted adsorbent can be easily separated from aqueous solutions. © 2016 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jece.2016.08.018
  • 2016 • 139 A versatile large-scale and green process for synthesizing magnetic nanoparticles with tunable magnetic hyperthermia features
    Simeonidis, K. and Liébana-Viñas, S. and Wiedwald, U. and Ma, Z. and Li, Z.-A. and Spasova, M. and Patsia, O. and Myrovali, E. and Makridis, A. and Sakellari, D. and Tsiaoussis, I. and Vourlias, G. and Farle, M. and Angelakeris, M.
    RSC Advances 6 53107-53117 (2016)
    This work proposes a large-scale synthesis methodology for engineered and functional magnetic nanoparticles (i.e. ferrites, sulfides) designed towards the principles of green and sustainable production combined with biomedical applicability. The experimental setup consists of a two-stage continuous-flow reactor in which single-crystalline nanoparticles are formed by the coprecipitation of metal salts in an aqueous environment. A series of optimized iron-based nanocrystals (Fe3O4, Fe3S4, CoFe2O4 and MnFe2O4) with diameters between 18 and 38 nm has been obtained. The samples were validated as potential magnetic hyperthermia agents by their heating efficiency as determined by specific loss power (SLP) in calorimetric experiments. In an effort to enhance colloidal stability and surface functionality, nanoparticles were coated by typical molecules of biomedical interest in a single step process. Finally, two-phase particle systems have been produced by a two-stage procedure to enhance the heating rate by the effective combination of different magnetic features. Results indicate relatively high SLP values for uncoated nanoparticles (420 W g-1 for Fe3O4) and a reduction of 20-60% in the heat dissipation rate upon covering by functional groups. Eventually, such effect was more than counterbalanced by the magnetic coupling of different phases in binary systems, since SLP was multiplied up to ∼1700 W g-1 for MnFe2O4/Fe3O4 suggesting a novel route to tune the efficiency of magnetic hyperthermia agents. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c6ra09362k
  • 2016 • 138 Optimization of a transferred arc reactor for metal nanoparticle synthesis
    Stein, M. and Kruis, F.E.
    Journal of Nanoparticle Research 18 (2016)
    The demand for metal nanoparticles is increasing strongly. Transferred arc synthesis is a promising process in this respect, as it shows high production rates, good quality particles and the ability of up-scaling. The influence of several process parameters on the performance of the process in terms of production rate and particle size is investigated. These parameters are the electrode design and adjustment, the gas flow rate and power input. A novel feeding mechanism allows process operation over an extended time period. It is shown that the process is capable of producing pure metal nanoparticles with variable primary particle sizes and comparatively high production rates. Optimal process conditions for a single transferred arc electrode pair are found, which allow further scale-up by numbering up. © 2016, The Author(s).
    view abstractdoi: 10.1007/s11051-016-3559-y
  • 2016 • 137 Characterizing the Effect of Multivalent Conjugates Composed of Aβ-Specific Ligands and Metal Nanoparticles on Neurotoxic Fibrillar Aggregation
    Streich, C. and Akkari, L. and Decker, C. and Bormann, J. and Rehbock, C. and Müller-Schiffmann, A. and Niemeyer, F.C. and Nagel-Steger, L. and Willbold, D. and Saccà, B. and Korth, C. and Schrader, T. and Barcikowski, S.
    ACS Nano 10 7582-7597 (2016)
    Therapeutically active small molecules represent promising nonimmunogenic alternatives to antibodies for specifically targeting disease-relevant receptors. However, a potential drawback compared to antibody-antigen interactions may be the lower affinity of small molecules toward receptors. Here, we overcome this low-affinity problem by coating the surface of nanoparticles (NPs) with multiple ligands. Specifically, we explored the use of gold and platinum nanoparticles to increase the binding affinity of Aβ-specific small molecules to inhibit Aβ peptide aggregation into fibrils in vitro. The interactions of bare NPs, free ligands, and NP-bound ligands with Aβ are comprehensively studied via physicochemical methods (spectroscopy, microscopy, immunologic tests) and cell assays. Reduction of thioflavin T fluorescence, as an indicator for β-sheet content, and inhibition of cellular Aβ excretion are even more effective with NP-bound ligands than with the free ligands. The results from this study may have implications in the development of therapeutics for treating Alzheimer's disease. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsnano.6b02627
  • 2016 • 136 Pilot-scale synthesis of metal nanoparticles by high-speed pulsed laser ablation in liquids
    Streubel, R. and Bendt, G. and Gökce, B.
    Nanotechnology 27 (2016)
    The synthesis of catalysis-relevant nanoparticles such as platinum and gold is demonstrated with productivities of 4 g h-1 for pulsed laser ablation in liquids (PLAL). The major drawback of low productivity of PLAL is overcome by utilizing a novel ultrafast high-repetition rate laser system combined with a polygon scanner that reaches scanning speeds up to 500 m s-1. This high scanning speed is exploited to spatially bypass the laser-induced cavitation bubbles at MHz-repetition rates resulting in an increase of the applicable, ablation-effective, repetition rate for PLAL by two orders of magnitude. The particle size, morphology and oxidation state of fully automated synthesized colloids are analyzed while the ablation mechanisms are studied for different laser fluences, repetition rates, interpulse distances, ablation times, volumetric flow rates and focus positions. It is found that at high scanning speeds and high repetition rate PLAL the ablation process is stable in crystallite size and decoupled from shielding and liquid effects that conventionally occur during low-speed PLAL. © 2016 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/27/20/205602
  • 2016 • 135 Interactions between metal species and nitrogen-functionalized carbon nanotubes
    Xia, W.
    Catalysis Science and Technology 6 630-644 (2016)
    Nitrogen-functionalized carbon nanotubes are promising materials in catalysis due to their versatile surface properties involving nitrogen groups, oxygen groups, surface defects and metal impurities. These factors can be used to tune the dispersion, morphology, crystal structure, electronic structure, mobility/stability and finally the catalytic performance of supported metal nanoparticles. This review focuses on selected examples aiming at understanding the interactions between surface groups, defects, and metal species and their impact on the catalytic properties in electrocatalysis and gas-phase redox catalysis. © 2016 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5cy01694k
  • 2016 • 134 Metal Nanoparticle-Catalyzed Reduction Using Borohydride in Aqueous Media: A Kinetic Analysis of the Surface Reaction by Microfluidic SERS
    Xie, W. and Grzeschik, R. and Schlücker, S.
    Angewandte Chemie - International Edition 55 13729-13733 (2016)
    Hydrides are widely used in reduction reactions. In protic solvents, their hydrolysis generates molecular hydrogen as a second reducing agent. The competition between these two parallel reduction pathways has been overlooked so far since both typically yield the same product. We investigated the platinum-catalyzed reduction of 4-nitrothiophenol to 4-aminothiophenol in aqueous sodium borohydride solution as a prominent model reaction, by using label-free SERS monitoring in a microfluidic reactor. Kinetic analysis revealed a strong pH dependence. Surprisingly, only at pH>13 the reduction is driven exclusively by sodium borohydride. This study demonstrates the potential of microfluidics-based kinetic SERS monitoring of heterogeneous catalysis in colloidal suspension. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201605776
  • 2016 • 133 Strong competition between electromagnetic enhancement and surface-energy-transfer induced quenching in plasmonic dye-sensitized solar cells: A generic yet controllable effect
    Yip, C.T. and Liu, X. and Hou, Y. and Xie, W. and He, J. and Schlücker, S. and Lei, D.Y. and Huang, H.
    Nano Energy 26 297-304 (2016)
    Light harvesting strategy using plasmonic metal nanostructures as subwavelength light concentrators provides a highly attractive solution to enhancing the performance of dye-sensitized solar cells (DSSCs). Through comprehensive optical spectroscopy and electrical characterizations together with a theoretical analysis, we demonstrate a strong competition between the surface energy transfer induced non-radiative quenching and the plasmonic electromagnetic enhancement effect in metal-dielectric-semiconductor core-shell-shell nanoparticle doped DSSCs, a generic yet unavoidable phenomenon in all types of plasmonic solar cells. The competition of the two effects results in a non-monotonic relationship between the device efficiency and the thickness of the dielectric shell covering the metal nanoparticles, and leads to an optimal thickness for the highest power conversion efficiency. This observation is further corroborated by photoluminescence spectroscopic measurements. Our experimental results are in good agreement with the Persson model that predicts a strong energy quenching effect when the distance between the photogenerated charge carrier and the metal core is short enough. Both experiment and theory show that the localized surface plasmon resonance enhanced light harvesting efficiency is suppressed by the surface energy transfer to the metal cores for the dielectric shell thickness shorter than a characteristic value (~7 nm in our study). Our work sheds new insights into the fundamental understanding of the photophysics mechanisms of plasmonic DSSCs and could push forward the study of plasmonic solar cells in terms of device design and fabrication. © 2016 Elsevier Ltd.
    view abstractdoi: 10.1016/j.nanoen.2016.05.016
  • 2015 • 132 Mapping near-field plasmonic interactions of silver particles with scanning near-field optical microscopy measurements
    Andrae, P. and Song, M. and Haggui, M. and Fumagalli, P. and Schmid, M.
    Proceedings of SPIE - The International Society for Optical Engineering 9547 (2015)
    A scanning near-field optical microscope (SNOM) is a powerful tool to investigate optical effects that are smaller than Abbe's limit. Its greatest strength is the simultaneous measurement of high-resolution topography and optical nearfield data that can be correlated to each other. However, the resolution of an aperture SNOM is always limited by the probe. It is a technical challenge to fabricate small illumination tips with a well-defined aperture and high transmission. The aperture size and the coating homogeneity will define the optical resolution and the optical image whereas the tip size and shape influence the topographic accuracy. Although the technique has been developing for many years, the correlation between simulated near-field data and measurement is still not convincing. To overcome this challenge, the mapping of near-field plasmonic interactions of silver nanoparticles is investigated. Different nanocluster samples with diverse distributions of silver particles are characterized via SNOM in illumination and collection mode. This will lead to topographical and optical images that can be used as an input for SNOM simulations with the aim of estimating optical artifacts. Including tip, particles, and substrate, our finite-elementmethod (FEM) simulations are based on the realistic geometry. Correlating the high-precision SNOM measurement and the detailed simulation of a full image scan will enable us to draw conclusions regarding near-field enhancements caused by interacting particles. © 2015 SPIE.
    view abstractdoi: 10.1117/12.2187358
  • 2015 • 131 Bioconjugated gold nanoparticles penetrate into spermatozoa depending on plasma membrane status
    Barchanski, A. and Taylor, U. and Sajti, C.L. and Gamrad, L. and Kues, W.A. and Rath, D. and Barcikowski, S.
    Journal of Biomedical Nanotechnology 11 1597-1607 (2015)
    Spermatozoa are not only essential for animal reproduction they also represent important tools for the manipulation of animal genetics. For instance, the genetic labeling and analysis of spermatozoa could provide a prospective complementation of pre-fertilization diagnosis and could help to prevent the inheritance of defective alleles during artificial insemination or to select beneficial traits in livestock. Spermatozoa feature extremely specialized membrane organization and restricted transport mechanisms making the labeling of genetically interesting DNA-sequences, e.g., with gold nanoparticles, a particular challenge. Here, we present a systematic study on the size-related internalization of ligand-free, monovalent and bivalent polydisperse gold nanoparticles, depending on spermatozoa membrane status. While monovalent conjugates were coupled solely to either negatively-charged oligonucleotides or positively-charged cell-penetrating peptides, bivalent conjugates were functionalized with both molecules simultaneously. The results clearly indicate that the cell membrane of acrosome-intact, bovine spermatozoa was neither permeable to ligand-free or oligonucleotide-conjugated nanoparticles, nor responsive to the mechanisms of cell-penetrating peptides. Interestingly, after acrosome reaction, which comprises major changes in sperm membrane composition, fluidity and charge, high numbers of monovalent and bivalent nanoparticles were found in the postequatorial segment, depicting a close and complex correlation between particle internalization and membrane organization. Additionally, depending on the applied peptide and for nanoparticle sizes <10 nm even a successive nuclear penetration was observed, making the bivalent conjugates promising for future genetic delivery and sorting issues. Copyright © 2015 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jbn.2015.2094
  • 2015 • 130 Metal-halide Nanoparticle Formation: Electrolytic and Chemical Synthesis of Mercury(I) Chloride Nanoparticles
    Bartlett, T.R. and Batchelor-Mcauley, C. and Tschulik, K. and Jurkschat, K. and Compton, R.G.
    ChemElectroChem 2 522-528 (2015)
    Mercury(I) chloride (Hg<inf>2</inf>Cl<inf>2</inf>) nanoparticles (NPs) are synthesised for the first time by using two different techniques. First, particles are formed by implosion of a calomel nanolayer, induced by partial electrolysis at a mercury hemisphere microelectrode. The resulting NPs are then characterised by the nanoimpact method, demonstrating the first time metal chloride NPs have been sized by this technique and showing the ability to form and study NPs insitu. Second, Hg<inf>2</inf>Cl<inf>2</inf> NPs are synthesised by using the precipitation reaction of Hg<inf>2</inf>(NO<inf>3</inf>)<inf>2</inf> with KCl. The NPs are characterised on both mercury and carbon microelectrodes and their size is found to agree with TEM results. Sizable studies: Mercury(I) chloride (Hg<inf>2</inf>Cl<inf>2</inf>) nanoparticles (NPs) are synthesised for the first time by using two different techniques. First, particles are formed by implosion of a calomel nanolayer, induced by partial electrolysis at a mercury hemisphere microelectrode. Second, Hg<inf>2</inf>Cl<inf>2</inf> NPs are synthesised by the precipitation reaction between Hg<inf>2</inf>(NO<inf>3</inf>)<inf>2</inf> and KCl. The NPs are characterised on both mercury and carbon microelectrodes by using the nanoimpact method and their size is found to agree with TEM results. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201402401
  • 2015 • 129 Coprecipitation: An excellent tool for the synthesis of supported metal catalysts - From the understanding of the well known recipes to new materials
    Behrens, M.
    Catalysis Today 246 46-54 (2015)
    Constant-pH co-precipitation is a standard synthesis technique for catalyst precursors. The general steps of this synthesis route are described in this work using the successfully applied industrial synthesis of the Cu/ZnO/(Al2O3) catalyst for methanol synthesis as an example. Therein, co-precipitation leads to well-defined and crystalline precursor compound with a mixed cationic lattice that contains all metal species of the final catalyst. The anions are thermally decomposed to give the mixed oxides and the noblest component, in this current case copper, finally segregates on a nano-metric level to yield supported and uniform metal nanoparticles. Recent examples of the application of this synthesis concept for supported catalysts are reported with an emphasis on the layered double hydroxide precursor (Cu,Zn,Al; Ni,Mg,Al; Pd,Mg,Al; Pd,Mg,Ga). This precursor material is very versatile and can lead to highly loaded base metal as well as to mono- and bi-metallic highly dispersed noble metal catalysts. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.cattod.2014.07.050
  • 2015 • 128 Wet-chemical synthesis of different bismuth telluride nanoparticles using metal organic precursors-single source vs. dual source approach
    Bendt, G. and Weber, A. and Heimann, S. and Assenmacher, W. and Prymak, O. and Schulz, S.
    Dalton Transactions 44 14272-14280 (2015)
    Thermolysis of the single source precursor (Et<inf>2</inf>Bi)<inf>2</inf>Te 1 in DIPB at 80 °C yielded phase-pure Bi<inf>4</inf>Te<inf>3</inf> nanoparticles, while mixtures of Bi<inf>4</inf>Te<inf>3</inf> and elemental Bi were formed at higher temperatures. In contrast, cubic Bi<inf>2</inf>Te particles were obtained by thermal decomposition of Et<inf>2</inf>BiTeEt 2 in DIPB. Moreover, a dual source approach (hot injection method) using the reaction of Te(SiEt<inf>3</inf>)<inf>2</inf> and Bi(NMe<inf>2</inf>)<inf>3</inf> was applied for the synthesis of different pure Bi-Te phases including Bi<inf>2</inf>Te, Bi<inf>4</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf>, which were characterized by PXRD, REM, TEM and EDX. The influence of reaction temperature, precursor molar ratio and thermolysis conditions on the resulting material phase was verified. Moreover, reactions of alternate bismuth precursors such as Bi(NEt<inf>2</inf>)<inf>3</inf>, Bi(NMeEt)<inf>3</inf> and BiCl<inf>3</inf> with Te(SiEt<inf>3</inf>)<inf>2</inf> were investigated. © 2015 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5dt02072g
  • 2015 • 127 Synthesis and characterization of antimicrobial textile finishing based on Ag:ZnO nanoparticles/chitosan biocomposites
    Buşilə, M. and Muşat, V. and Textor, T. and Mahltig, B.
    RSC Advances 5 21562-21571 (2015)
    ZnO and Ag:ZnO nanoparticles were prepared by hydrolysis of zinc acetate in the presence of lithium hydroxide (LiOH). In combination with binders based on hybrid polymer sols, these metal oxide materials were applied for textile treatment. Hybrid coatings based on ZnO, Ag:ZnO/CS, chitosan (CS), 3-glycidyloxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) prepared by sol-gel method were applied on cotton 100% and cotton/polyester (50/50%) textiles using "pad-dry-cure" technique. The obtained nanoparticles incorporated within chitosan matrix were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), UV-Vis spectroscopy and field emission scanning electron microscopy (FE-SEM). The antimicrobial activity of Ag/CS, ZnO/CS and Ag:ZnO/CS composite coatings was investigated in comparison to that of the pure chitosan using the paper disc method on Mueller-Hinton agar, against the Gram-negative E. coli and the Gram-positive S. aureus bacteria. For the same composite coatings applied on textile, the antimicrobial activity was investigated by UV-Vis absorption spectroscopy using TTC method, against the bacteria E. coli and M. luteus. The investigated nanocomposite materials showed good antimicrobial activity and are promising materials for use as medical applications. This journal is © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c4ra13918f
  • 2015 • 126 Laser-based in situ measurement and simulation of gas-phase temperature and iron atom concentration in a pilot-plant nanoparticle synthesis reactor
    Feroughi, O.M. and Hardt, S. and Wlokas, I. and Hülser, T. and Wiggers, H. and Dreier, T. and Schulz, C.
    Proceedings of the Combustion Institute 35 2299-2306 (2015)
    A scaled-up flame reactor for nanoparticle synthesis was investigated through a combination of in-situ laser-induced fluorescence (LIF) measurements and computational fluid dynamics (CFD) simulations with detailed chemistry. Multi-line NO-LIF was used for imaging gas-temperature and Fe-LIF for measurement of iron atom concentration. Despite the challenging environment of production reactors in an industrial environment, various conditions for stable flames with different gas flows with and without adding Fe(CO)5 as precursor for the synthesis of iron-oxide nanoparticles were investigated. In contrast to previous measurements in laminar lab-scale flames, a second mechanism for forming iron oxide nanoparticles was found via intermediate formation of iron clusters and elemental iron particles in hot, oxygen-free gas streams followed by subsequent oxidation. © 2014 Published by Elsevier Inc. on behalf of The Combustion Institute.
    view abstractdoi: 10.1016/j.proci.2014.05.039
  • 2015 • 125 Ligand-free Gold Nanoparticles as a Reference Material for Kinetic Modelling of Catalytic Reduction of 4-Nitrophenol
    Gu, S. and Kaiser, J. and Marzun, G. and Ott, A. and Lu, Y. and Ballauff, M. and Zaccone, A. and Barcikowski, S. and Wagener, P.
    Catalysis Letters 145 1105-1112 (2015)
    The reduction of 4-nitrophenol by sodium borohydride is a common model reaction to test the catalytic activity of metal nanoparticles. As all reaction steps proceed solely on the surface of the metal nanoparticles (Langmuir-Hinshelwood model), ligand-coverage of metal nanoparticles impedes the merging of theory and experiment. Therefore we analyzed the catalytic activity of bare gold nanoparticles prepared by laser ablation in liquid without any stabilizers or ligands. The catalytic reaction is characterized by a full kinetic analysis including 4-hydroxylaminophenol as an intermediate species. Excellent agreement between theory and experiment is found. Moreover, the suspension of the nanoparticles remains stable. Hence, ligand-free nanoparticles can be used as a reference material for mechanistic studies of catalytic reactions. In addition, the analysis shows that gold nanoparticles synthesized by laser ablation are among the most active catalysts for this reaction. (Graph Presented). © 2015 Springer Science+Business Media.
    view abstractdoi: 10.1007/s10562-015-1514-7
  • 2015 • 124 Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship
    Guo, Y. and Gu, D. and Jin, Z. and Du, P.-P. and Si, R. and Tao, J. and Xu, W.-Q. and Huang, Y.-Y. and Senanayake, S. and Song, Q.-S. and Jia, C.-J. and Schüth, F.
    Nanoscale 7 4920-4928 (2015)
    Uniform Au nanoparticles (∼2 nm) with narrow size-distribution (standard deviation: 0.5-0.6 nm) supported on both hydroxylated (Fe-OH) and dehydrated iron oxide (Fe-O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed high homogeneity in the supported Au nanoparticles. The ex situ and in situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H<inf>2</inf>-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe-OH < Au/Fe-O) and CD (Au/Fe-OH > Au/Fe-O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe-OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeO<inf>x</inf> catalysts with very similar structural characteristics in CO oxidation. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4nr06967f
  • 2015 • 123 A rapid, high-yield and large-scale synthesis of uniform spherical silver nanoparticles by a microwave-assisted polyol process
    Helmlinger, J. and Heise, M. and Heggen, M. and Ruck, M. and Epple, M.
    RSC Advances 5 92144-92150 (2015)
    Silver nanoparticles are often employed in medical devices and consumer products due to their antibacterial action. For this, reliable syntheses with quantitative yield are required. Uniform spherical silver nanoparticles with a diameter of about 180 nm were synthesized by carrying out the polyol synthesis in a microwave. Silver nitrate was dissolved in ethylene glycol and poly(N-vinyl pyrrolidone) (PVP) was added as capping agent. The particles were characterized by SEM, HRTEM, XRD, and DLS. The results are compared with the classical method where silver nitrate is reduced by glucose in aqueous solution, heated with an oil-bath. The microwave-assisted synthesis leads to an almost quantitative yield of uniform silver nanoparticles after 20 min reaction time and gives exclusively spherical particles without other shapes like triangles, rods or prisms. Diethylene glycol as solvent gave a more homogeneous particle size distribution than ethylene glycol. For both kinds of particles, dissolution in ultrapure water was examined over a period of 29 days in the presence of oxygen. The dissolution was comparable in both cases (about 50% after 4 weeks), indicating the same antibacterial action for particles from the microwave and from the glucose synthesis. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5ra20446a
  • 2015 • 122 CO oxidation as a test reaction for strong metal-support interaction in nanostructured Pd/FeOx powder catalysts
    Kast, P. and Friedrich, M. and Teschner, D. and Girgsdies, F. and Lunkenbein, T. and D'Alnoncourt, R.N. and Behrens, M. and Schlögl, R.
    Applied Catalysis A: General 502 8-17 (2015)
    A series of differently loaded palladium-iron catalysts was prepared by a controlled co-precipitation method of the nitrate precursors, in order to ensure homogeneous Pd particle size-distribution. After characterization of the pre-catalysts by various techniques, different controlled reduction conditions were applied to investigate the interactions within the Pd-iron system, containing reversible and irreversible processes like phase transformations, SMSI, sintering and alloying. Strong indications for the reversible surface decoration of the Pd nanoparticles with iron oxide species via strong metal-support interaction were found by the combined results of DRIFTS, CO-chemisorption, TEM and XPS measurements. This SMSI state was found to be unstable. It was observed independent of bulk phase or palladium particle size. Catalytic CO-oxidation was found to be a suitable test reaction for the study of the phenomenon: higher activity as well as oxidative deactivation of the SMSI state was observed by investigating the light-off behavior in repeated, temperature-programmed cycles as well as by isothermal measurements. The instability was found to be higher in case of higher Pd dispersion. In addition, bulk properties of the Pd-Fe system, like alloying, were investigated by detailed XRD measurements. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apcata.2015.04.010
  • 2015 • 121 Plasma synthesis of titanium nitride, carbide and carbonitride nanoparticles by means of reactive anodic arc evaporation from solid titanium
    Kiesler, D. and Bastuck, T. and Theissmann, R. and Kruis, F.E.
    Journal of Nanoparticle Research 17 (2015)
    Plasma methods using the direct evaporation of a transition metal are well suited for the cost-efficient production of ceramic nanoparticles. In this paper, we report on the development of a simple setup for the production of titanium-ceramics by reactive anodic arc evaporation and the characterization of the aerosol as well as the nanopowder. It is the first report on TiCXN1 − X synthesis in a simple anodic arc plasma. By means of extensive variations of the gas composition, it is shown that the composition of the particles can be tuned from titanium nitride over a titanium carbonitride phase (TiCXN1 − X) to titanium carbide as proven by XRD data. The composition of the plasma gas especially a very low concentration of hydrocarbons around 0.2 % of the total plasma gas is crucial to tune the composition and to avoid the formation of free carbon. Examination of the particles by HR-TEM shows that the material consists mostly of cubic single crystalline particles with mean sizes between 8 and 27 nm. © 2015, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-015-2967-8
  • 2015 • 120 Continuous electrophoretic deposition and electrophoretic mobility of ligand-free, metal nanoparticles in liquid flow
    Koenen, S. and Streubel, R. and Jakobi, J. and Schwabe, K. and Krauss, J.K. and Barcikowski, S.
    Journal of the Electrochemical Society 162 D174-D179 (2015)
    Direct current electrophoretic deposition (DC-EPD) of ligand-free metal nanoparticles in a flow-through reactor is studied by analyzing the educt colloid and the outflow of the flow through chamber while the concentration of the colloid and the strength of the electric field is varied.Metal nanoparticles synthesized by pulsed laser ablation in liquid (PLAL) are used to ensure that the colloidal nanoparticle surface is free of any ligands and that the colloid's stability and movement in an electric field is solely influenced by electrostatic forces. Electrophoretic mobility and deposition kinetics of these ligand-free nanoparticles on plain surfaces are examined for different electric field strengths. Additionally, a continuous liquid flow DC-EPD process is presented and optimized regarding deposition rate, colloid stability, and liquid flow rate. The reported parameter window for high deposition rates of nanoparticles without a negative impact on the colloid, allows to define an efficient stationary EPD process suitable for high throughput applications. © 2015 The Electrochemical Society.
    view abstractdoi: 10.1149/2.0811504jes
  • 2015 • 119 Unveiling the correlation between nanometer-thick molecular monolayer sensitivity and near-field enhancement and localization in coupled plasmonic oligomers
    König, M. and Rahmani, M. and Zhang, L. and Lei, D.Y. and Roschuk, T.R. and Giannini, V. and Qiu, C.-W. and Hong, M. and Schlücker, S. and Maier, S.A.
    ACS Nano 8 9188-9198 (2015)
    Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic hot spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/nn5028714
  • 2015 • 118 Raman-encoded microbeads for spectral multiplexing with SERS detection
    Lai, Y. and Sun, S. and He, T. and Schlücker, S. and Wang, Y.
    RSC Advances 5 13762-13767 (2015)
    Simultaneous detection of multiple molecular targets can greatly facilitate early diagnosis and drug discovery. Encoding micron-sized beads with optically active tags is one of the most popular methods to achieve multiplexing. Noble metal nanoparticle labels for optical detection by surface-enhanced Raman spectroscopy (SERS) exhibit narrow bandwidths, high photostability and intense Raman signals. In this study, we demonstrate the feasibility of spectral multiplexing by SERS using micron-sized polystyrene (PS) beads loaded with SERS-active nanoparticles. The silica-encapsulated SERS nanotags comprise gold nanocrystals with a self-assembled monolayer (SAM) of aromatic thiols as Raman reporter molecules for spectral identification. SERS microspectroscopic images of single Raman-encoded PS microbeads indicate the homogeneous spatial distribution of the SERS-active nanoparticles on the surface of the beads. By using up to five different Raman reporters, 31 spectrally distinct micron-sized beads were encoded and characterized spectroscopically at the single-bead level. This journal is © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c4ra16163g
  • 2015 • 117 Phase transitions during formation of Ag nanoparticles on In2S3 precursor layers
    Liu, Y. and Fu, Y. and Dittrich, T. and Sáez-Araoz, R. and Schmid, M. and Hinrichs, V. and Lux-Steiner, M.C. and Fischer, C.-H.
    Thin Solid Films 590 54-59 (2015)
    Phase transitions have been investigated for silver deposition onto In<inf>2</inf>S<inf>3</inf> precursor layers by spray chemical vapor deposition from a trimethylphosphine (hexafluoroacetylacetonato) silver (Ag(hfacac)(PMe<inf>3</inf>)) solution. The formation of Ag nanoparticles (Ag NPs) on top of the semiconductor layer set on concomitant with the formation of AgIn<inf>5</inf>S<inf>8</inf>. The increase of the diameter of Ag NPs was accompanied by the evolution of orthorhombic AgInS<inf>2</inf>. The formation of Ag<inf>2</inf>S at the interface between Ag NPs and the semiconductor layer was observed. Surface photovoltage spectroscopy indicated charge separation and electronic transitions in the ranges of corresponding band gaps. The phase transition approach is aimed to be applied for the formation of plasmonic nanostructures on top of extremely thin semiconducting layers. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2015.07.021
  • 2015 • 116 Assembling Paramagnetic Ceruloplasmin at Electrode Surfaces Covered with Ferromagnetic Nanoparticles. Scanning Electrochemical Microscopy in the Presence of a Magnetic Field
    Matysiak, E. and Botz, A.J.R. and Clausmeyer, J. and Wagner, B. and Schuhmann, W. and Stojek, Z. and Nowicka, A.M.
    Langmuir 31 8176-8183 (2015)
    Adsorption of ceruloplasmin (Cp) at a gold electrode modified with ferromagnetic iron nanoparticles encapsulated in carbon (Fe@C Nps) leads to a successful immobilization of the enzyme in its electroactive form. The proper placement of Cp at the electrode surface on top of the nanocapsules containing an iron core allowed a preorientation of the enzyme, hence allowing direct electron transfer between the electrode and the enzyme. Laser ablation coupled with inductively coupled plasma mass spectrometry indicated that Cp was predominantly located at the paramagnetic nanoparticles. Scanning electrochemical microscopy measurements in the sample-generation/tip-collection mode proved that Cp was ferrooxidative inactive if it was immobilized on the bare gold surface and reached the highest activity if it was adsorbed on Fe@C Nps in the presence of a magnetic field. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b01155
  • 2015 • 115 Cysteine-containing oligopeptide β-sheets as redispersants for agglomerated metal nanoparticles
    Mizutaru, T. and Sakuraba, T. and Nakayama, T. and Marzun, G. and Wagener, P. and Rehbock, C. and Barcikowski, S. and Murakami, K. and Fujita, J. and Ishii, N. and Yamamoto, Y.
    Journal of Materials Chemistry A 3 17612-17619 (2015)
    Oligopeptide β-sheets comprising a fluorenyl methoxy carbonyl (Fmoc) group on its N-terminus and five amino acid residues of cysteine, lysine and valine displays redispersive properties with respect to agglomerated metal nanoparticles (MNPs, M = Au, Cu, Pt and Pd). The ligand-free MNPs prepared by a laser ablation technique in liquid maintain a high dispersion state due to the inherent surface charges delivered by anionic species present in solution, but may agglomerate after the preparation depending on concentration or salinity. We show how the agglomerated MNPs can be returned to the dispersed state by adding the Fmoc-oligopeptide β-sheets in methanol, as characterized by photoabsorption spectroscopy and transmission electron microscopy. Systematic studies in which we vary the concentration, the amino acid sequences and the secondary structures of a series of the oligopeptides clarify that the β-sheet structure is essential for the redispersion of the MNPs, where metal-binding thiol groups are integrated on one side and positively charged amino groups are located on the other side of the β-sheet. A possible mechanism for the redispersion may be that the agglomerated MNPs are subsequently enwrapped by the flexible β-sheets and gradually separated due to the reconstruction of peptide β-sheets under the assembly/disassembly equilibrium. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5ta02098k
  • 2015 • 114 Nanostructure of wet-chemically prepared, polymer-stabilized silver-gold nanoalloys (6 nm) over the entire composition range
    Ristig, S. and Prymak, O. and Loza, K. and Gocyla, M. and Meyer-Zaika, W. and Heggen, M. and Raabe, D. and Epple, M.
    Journal of Materials Chemistry B 3 4654-4662 (2015)
    Bimetallic silver-gold nanoparticles were prepared by co-reduction using citrate and tannic acid in aqueous solution and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). The full composition range of silver:gold from 0:100 to 100:0 (n:n) was prepared with steps of 10 mol%. The nanoparticles were spherical, monodispersed, and had a diameter of ∼6 nm, except for Ag:Au 90:10 nanoparticles and pure Ag nanoparticles which were slightly larger. The size of the nanoalloys was determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). By means of X-ray powder diffraction (XRD) together with Rietveld refinement, precise lattice parameters, crystallite size and microstrain were determined. Scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) showed that the particles consisted of a gold-rich core and a silver-rich shell. XRD and DCS indicated that the nanoparticles were not twinned, except for pure Ag and Ag:Au 90:10, although different domains were visible in the TEM. A remarkable negative deviation from Vegard's linear rule of alloy mixtures was observed (isotropic contraction of the cubic unit cell with a minimum at a 50:50 composition). This effect was also found for Ag:Au bulk alloys, but it was much more pronounced for the nanoalloys. Notably, it was much less pronounced for pure silver and gold nanoparticles. The microstrain was increased along with the contraction of the unit cell with a broad maximum at a 50:50 composition. The synthesis is based on aqueous solvents and can be easily scaled up to a yield of several mg of a well dispersed nanoalloy with application potential due to its tuneable antibacterial action (silver) and its optical properties for bioimaging. © The Royal Society of Chemistry 2015.
    view abstractdoi: 10.1039/c5tb00644a
  • 2015 • 113 Synthesis, characterization and in vitro effects of 7 nm alloyed silver-gold nanoparticles
    Ristig, S. and Chernousova, S. and Meyer-Zaika, W. and Epple, M.
    Beilstein Journal of Nanotechnology 6 1212-1220 (2015)
    Alloyed silver-gold nanoparticles were prepared in nine different metal compositions with silver/gold molar ratios of ranging from 90:10 to 10:90. The one-pot synthesis in aqueous medium can easily be modified to gain control over the final particle diameter and the stabilizing agents. The purification of the particles to remove synthesis by-products (which is an important factor for subsequent in vitro experiments) was carried out by multiple ultracentrifugation steps. Characterization by transmission electron microscopy (TEM), differential centrifugal sedimentation (DCS), dynamic light scattering (DLS), UV-vis spectroscopy and atomic absorption spectroscopy (AAS) showed spherical, monodisperse, colloidally stable silver-gold nanoparticles of ≈7 nm diameter with measured molar metal compositions very close to the theoretical values. The examination of the nanoparticle cytotoxicity towards HeLa cells and human mesenchymal stem cells (hMSCs) showed that the toxicity is not proportional to the silver content. Nanoparticles with a silver/gold molar composition of 80:20 showed the highest toxicity. © 2015 Ristig et al.
    view abstractdoi: 10.3762/bjnano.6.124
  • 2015 • 112 Nano-optical concept design for light management
    Schmid, M. and Tsakanikas, S. and Mangalgiri, G. and Andrae, P. and Song, M. and Yin, G. and Riedel, W. and Manley, P.
    Proceedings of SPIE - The International Society for Optical Engineering 9626 (2015)
    Efficient light management in optoelectronic devices requires nanosystems where high optical qualities coincide with suitable device integration. The requirement of chemical and electrical passivation for integrating nanostrutures in e.g.Thin film solar cells points towards the use of insulating and stable dielectric material, which however has to provide high scattering and near-fields as well. We investigate metal@dielectric core-shell nanoparticles and dielectric nanorods. Whereas core-shell nanoparticles can be simulated using Mie theory, nanorods of finite length are studied with the finite element method. We reveal that a metallic core within a thin dielectric shell can help to enhance scattering and near-field cross sections compared to a bare dielectric nanoparticle of the same radius. A dielectric nanorod has the benefit over a dielectric nanosphere in that it can generate much higher scattering cross sections and also give rise to a high near-field enhancement along its whole length. Electrical benefits of e.g. Ag@oxide nanoparticles in thin-film solar cells and ZnO nanorods in hybrid devices lie in reduction of recombination centers or close contact of the nanorod material with the surrounding organics, respectively. The optical benefit of dielectric shell material and elongated dielectric nanostructures is highlighted in this paper. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
    view abstractdoi: 10.1117/12.2191081
  • 2015 • 111 Process engineering of nanoparticles below 20 nm—a fundamental discussion of characterization, particle formation, stability and post processing
    Segets, D. and Peukert, W.
    Colloid Process Engineering 279-305 (2015)
    In the following chapter fundamental aspects that have to be considered during the processing of small nanoparticles will be addressed. We investigated quantum confined manganese doped ZnS, ZnO, PbS and PbSe semiconductor nanoparticles, so-called quantum dots (QDs) and silver noble metal nanorods. All materials were chosen due to their technical relevance for future applications in the emerging fields of solar cells, sensors and diagnostics as well as due to the possibility of their in situ characterization by UV/Vis absorbance spectroscopy. After a brief introduction to the specific prospects and challenges of these materials we will focus on the important processing issues that need to be solved for producing these particles at high quality on a larger scale: (i) the modelling of particle formation including nucleation, growth and ripening based on a mechanistic understanding and on experimentally derived data on solubility and surface energies, (ii) the stabilization of nanoparticles not only against agglomeration but also against shape changes and (iii) classification. The latter is realized by size selective precipitation which allows surprisingly sharp separations (κ= 0.75) of particles with only a few nm in diameter. Although the extremely small particle sizes (feed PSD between 1.5 and 3 nm), classification results were successfully analyzed by well-known concepts from particle technology. Our results are seen to be an essential contribution to colloidal processing. They enable a future optimization of process parameters by a knowledge-based design strategy that can be applied within continuous as well as automatized batch reactor concepts. © Springer International Publishing Switzerland 2015.
    view abstractdoi: 10.1007/978-3-319-15129-8_12
  • 2015 • 110 Electrochemical detection of single E. coli bacteria labeled with silver nanoparticles
    Sepunaru, L. and Tschulik, K. and Batchelor-McAuley, C. and Gavish, R. and Compton, R.G.
    Biomaterials Science 3 816-820 (2015)
    A proof-of-concept for the electrochemical detection of single Escherichia coli bacteria decorated with silver nanoparticles is reported. Impacts of bacteria with an electrode - held at a suitably oxidizing potential - lead to an accompanying burst of current with each collision event. The frequency of impacts scales with the concentration of bacteria and the charge indicates the extent of decoration. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5bm00114e
  • 2015 • 109 One-Pot Synthesis of Carbon-Coated Nanostructured Iron Oxide on Few-Layer Graphene for Lithium-Ion Batteries
    Sun, Z. and Madej, E. and Wiktor, C. and Sinev, I. and Fischer, R.A. and Van Tendeloo, G. and Muhler, M. and Schuhmann, W. and Ventosa, E.
    Chemistry - A European Journal 21 16154-16161 (2015)
    Nanostructure engineering has been demonstrated to improve the electrochemical performance of iron oxide based electrodes in Li-ion batteries (LIBs). However, the synthesis of advanced functional materials often requires multiple steps. Herein, we present a facile one-pot synthesis of carbon-coated nanostructured iron oxide on few-layer graphene through high-pressure pyrolysis of ferrocene in the presence of pristine graphene. The ferrocene precursor supplies both iron and carbon to form the carbon-coated iron oxide, while the graphene acts as a high-surface-area anchor to achieve small metal oxide nanoparticles. When evaluated as a negative-electrode material for LIBs, our composite showed improved electrochemical performance compared to commercial iron oxide nanopowders, especially at fast charge/discharge rates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201501935
  • 2015 • 108 Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro
    Surmeneva, M.A. and Kleinhans, C. and Vacun, G. and Kluger, P.J. and Schönhaar, V. and Müller, M. and Hein, S.B. and Wittmar, A. and Ulbricht, M. and Prymak, O. and Oehr, C. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 135 386-393 (2015)
    Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24 h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2015.07.057
  • 2015 • 107 Nanoparticle Capping Agent Dynamics and Electron Transfer: Polymer-Gated Oxidation of Silver Nanoparticles
    Tanner, E.E.L. and Tschulik, K. and Tahany, R. and Jurkschat, K. and Batchelor-McAuley, C. and Compton, R.G.
    Journal of Physical Chemistry C 119 18808-18815 (2015)
    Capping agent-controlled stability of nanoparticles tailors them for different applications, but the associated particle-solvent dynamics are poorly understood. Herein, previously unseen capping agent-gated nanoparticle redox activity is observed for poly(ethylene glycol)-coated silver nanoparticles. This is revealed by stochastic nanoparticle stripping, probing one individual nanoparticle at a time, from an ensemble of surface-immobilized nanoparticles. Thus, new and previously inaccessible understanding is gained on the crucial role of capping agent dynamics on nanoparticle reactivity. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b05789
  • 2015 • 106 Non-Invasive Probing of Nanoparticle Electrostatics
    Tschulik, K. and Cheng, W. and Batchelor-Mcauley, C. and Murphy, S. and Omanović, D. and Compton, R.G.
    ChemElectroChem 2 112-118 (2015)
    Electrostatic interactions between surface-charged nanoparticles (NPs) and electrodes studied using existing techniques unavoidably and significantly alter the system being analyzed. Here we present a methodology that allows the probing of unperturbed electrostatic interactions between individual NPs and charged surfaces. The uniqueness of this approach is that stochastic NP impact events are used as the probe. During a single impact, only an attomole of the redox species reacts and is released at the interface during each sensing event. As an example, the effect of electrostatic screening on the reduction of negatively charged indigo NPs at a mercury microelectrode is explored at potentials positive and negative of the potential of zero charge. At suitable overpotentials fully driven electron transfer is seen for all but very low (<0.005M) ionic strengths. The loss of charge transfer in such dilute electrolytes is unambiguously shown to arise from a reduced driving force for the reaction rather than a reduced population of NPs near the electrode, contradicting popular perceptions. Electrostatics were found not to significantly affect the reactivity of the studied NPs. Importantly, the presented technique is general and can be applied to a wide variety of NPs, including metals, metal oxides and organic compounds. Not what you might think: A new and non-invasive technique to probe the electrostatic interaction between surface-charged nanoparticles and a charged metal/solution interface shows that electrostatic effects are insignificant in all but very dilute electrolytes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201402285
  • 2015 • 105 Simultaneous Analysis of Hydrodynamic and Optical Properties Using Analytical Ultracentrifugation Equipped with Multiwavelength Detection
    Walter, J. and Sherwood, P.J. and Lin, W. and Segets, D. and Stafford, W.F. and Peukert, W.
    Analytical Chemistry 87 3396-3403 (2015)
    Analytical ultracentrifugation (AUC) has proven to be a powerful tool for the study of particle size distributions, particle shapes, and interactions with high accuracy and unrevealed resolution. In this work we show how the analysis of sedimentation velocity data from the AUC equipped with a multiwavelength detector (MWL) can be used to gain an even deeper understanding of colloidal and macromolecular mixtures. New data evaluation routines have been integrated in the software SEDANAL to allow for the handling of MWL data. This opens up a variety of new possibilities because spectroscopic information becomes available for individual components in mixtures at the same time using MWL-AUC. For systems of known optical properties information on the hydrodynamic properties of the individual components in a mixture becomes accessible. For the first time, the determination of individual extinction spectra of components in mixtures is demonstrated via MWL evaluation of sedimentation velocity data. In our paper we first provide the informational background for the data analysis and expose the accessible parameters of our methodology. We further demonstrate the data evaluation by means of simulated data. Finally, we give two examples which are highly relevant in the field of nanotechnology using colored silica and gold nanoparticles of different size and extinction properties. (Figure Presented). © 2015 American Chemical Society.
    view abstractdoi: 10.1021/ac504649c
  • 2015 • 104 Biocompatible microgel-modified electrospun fibers for zinc ion release
    Wilke, P. and Coger, V. and Nachev, M. and Schachschal, S. and Million, N. and Barcikowski, S. and Sures, B. and Reimers, K. and Vogt, P.M. and Pich, A.
    Polymer (United Kingdom) 61 163-173 (2015)
    We present a novel and facile method for the design of biocompatible microgel-modified microfibers loaded with ZnO nanoparticles capable of zinc ion release under physiological conditions. The microfibers consist of three materials hierarchically assembled in a controlled and reproducible way. We synthesized poly(N-vinylcaprolactam-co-itaconic acid) aqueous microgels with carboxylic groups located in the microgel core. The obtained microgels can be loaded with various amounts of ZnO nanoparticles by in-situ growth of ZnO in microgels. As shown by electrophoretic mobility and TEM measurements, ZnO nanoparticles are selectively loaded in the microgel core and stabilized by itaconic acid groups bearing strong negative charges. ZnO-loaded microgels were used as functional additive to produce poly(ε-caprolactone) (PCL) microfibers using the electrospinning process. The resulting microfibers consist of a PCL core coated with the microgels located at the surface of the fibers. The variation of the ZnO amount loaded into microgels allows regulating the ZnO content in microfibers and gives the possibility to tune the released amount of zinc ions in aqueous medium at pH 7.5 and 37 °C. We demonstrate that the obtained functional microfibers are biocompatible and non-toxic, thus being good candidates for biomedical applications like scaffolds for tissue engineering, biointerface coatings or wound closing dressings. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2015.01.078
  • 2015 • 103 Co3O4-MnO2-CNT Hybrids Synthesized by HNO3 Vapor Oxidation of Catalytically Grown CNTs as OER Electrocatalysts
    Xie, K. and Masa, J. and Madej, E. and Yang, F. and Weide, P. and Dong, W. and Muhler, M. and Schuhmann, W. and Xia, W.
    ChemCatChem 7 3027-3035 (2015)
    An efficient two-step gas-phase method was developed for the synthesis of Co<inf>3</inf>O<inf>4</inf>-MnO<inf>2</inf>-CNT hybrids used as electrocatalysts in the oxygen evolution reaction (OER). Spinel Co-Mn oxide was used for the catalytic growth of multiwalled carbon nanotubes (CNTs) and the amount of metal species remaining in the CNTs was adjusted by varying the growth time. Gas-phase treatment in HNO<inf>3</inf> vapor at 200 °C was performed to 1)open the CNTs, 2)oxidize encapsulated Co nanoparticles to Co<inf>3</inf>O<inf>4</inf> as well as MnO nanoparticles to MnO<inf>2</inf>, and 3)to create oxygen functional groups on carbon. The hybrid demonstrated excellent OER activity and stability up to 37.5h under alkaline conditions, with longer exposure to HNO<inf>3</inf> vapor up to 72h beneficial for improved electrocatalytic properties. The excellent OER performance can be assigned to the high oxidation states of the oxide nanoparticles, the strong electrical coupling between these oxides and the CNTs as well as favorable surface properties rendering the hybrids a promising alternative to noble metal based OER catalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cctc.201500469
  • 2015 • 102 Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se2 solar cells
    Yin, G. and Steigert, A. and Andrae, P. and Goebelt, M. and Latzel, M. and Manley, P. and Lauermann, I. and Christiansen, S. and Schmid, M.
    Applied Surface Science 355 800-804 (2015)
    Integration of plasmonic Ag nanoparticles as a back reflector in ultra-thin Cu(In,Ga)Se2 (CIGSe) solar cells is investigated. X-ray photoelectron spectroscopy results show that Ag nanoparticles underneath a Sn:In2O3 back contact could not be thermally passivated even at a low substrate temperature of 440 °C during CIGSe deposition. It is shown that a 50 nm thick Al2O3 film prepared by atomic layer deposition is able to block the diffusion of Ag, clearing the thermal obstacle in utilizing Ag nanoparticles as a back reflector in ultra-thin CIGSe solar cells. Via 3-D finite element optical simulation, it is proved that the Ag nanoparticles show the potential to contribute the effective absorption in CIGSe solar cells. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.07.195
  • 2015 • 101 Light Induced H2 Evolution from a Biophotocathode Based on Photosystem 1 - Pt Nanoparticles Complexes Integrated in Solvated Redox Polymers Films
    Zhao, F. and Conzuelo, F. and Hartmann, V. and Li, H. and Nowaczyk, M.M. and Plumeré, N. and Rögner, M. and Schuhmann, W.
    Journal of Physical Chemistry B 119 13726-13731 (2015)
    We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)2Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 ± 0.4 μA cm-2) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H2 evolution. Direct evidence for the latter process is provided by monitoring the H2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcb.5b03511
  • 2014 • 100 PVP-coated, negatively charged silver nanoparticles: A multi-center study of their physicochemical characteristics, cell culture and in vivo experiments
    Ahlberg, S. and Antonopulos, A. and Diendorf, J. and Dringen, R. and Epple, M. and Flöck, R. and Goedecke, W. and Graf, C. and Haberl, N. and Helmlinger, J. and Herzog, F. and Heuer, F. and Hirn, S. and Johannes, C. and Kittler, ...
    Beilstein Journal of Nanotechnology 5 1944-1965 (2014)
    PVP-capped silver nanoparticles with a diameter of the metallic core of 70 nm, a hydrodynamic diameter of 120 nm and a zeta potential of -20 mV were prepared and investigated with regard to their biological activity. This review summarizes the physicochemical properties (dissolution, protein adsorption, dispersability) of these nanoparticles and the cellular consequences of the exposure of a broad range of biological test systems to this defined type of silver nanoparticles. Silver nanoparticles dissolve in water in the presence of oxygen. In addition, in biological media (i.e., in the presence of proteins) the surface of silver nanoparticles is rapidly coated by a protein corona that influences their physicochemical and biological properties including cellular uptake. Silver nanoparticles are taken up by cell-type specific endocytosis pathways as demonstrated for hMSC, primary T-cells, primary monocytes, and astrocytes. A visualization of particles inside cells is possible by X-ray microscopy, fluorescence microscopy, and combined FIB/SEM analysis. By staining organelles, their localization inside the cell can be additionally determined. While primary brain astrocytes are shown to be fairly tolerant toward silver nanoparticles, silver nanoparticles induce the formation of DNA double-strand-breaks (DSB) and lead to chromosomal aberrations and sister-chromatid exchanges in Chinese hamster fibroblast cell lines (CHO9, K1, V79B). An exposure of rats to silver nanoparticles in vivo induced a moderate pulmonary toxicity, however, only at rather high concentrations. The same was found in precision-cut lung slices of rats in which silver nanoparticles remained mainly at the tissue surface. In a human 3D triple-cell culture model consisting of three cell types (alveolar epithelial cells, macrophages, and dendritic cells), adverse effects were also only found at high silver concentrations. The silver ions that are released from silver nanoparticles may be harmful to skin with disrupted barrier (e.g., wounds) and induce oxidative stress in skin cells (HaCaT). In conclusion, the data obtained on the effects of this well-defined type of silver nanoparticles on various biological systems clearly demonstrate that cell-type specific properties as well as experimental conditions determine the biocompatibility of and the cellular responses to an exposure with silver nanoparticles. © 2014 Ahlberg et al.
    view abstractdoi: 10.3762/bjnano.5.205
  • 2014 • 99 Comparison of silver nanoparticles stored under air or argon with respect to the induction of intracellular free radicals and toxic effects toward keratinocytes
    Ahlberg, S. and Meinke, M.C. and Werner, L. and Epple, M. and Diendorf, J. and Blume-Peytavi, U. and Lademann, J. and Vogt, A. and Rancan, F.
    European Journal of Pharmaceutics and Biopharmaceutics 88 651-657 (2014)
    Bacterial infections decreased considerably after the discovery of antibiotics. Nevertheless, because of the rising rate of infections caused by antibiotic-resistant bacteria strains, the search for new bactericidal agents has again become a crucial topic in clinical medicine. Silver nanoparticles (AgNP) have a huge potential in dermatology and wound care management because of their ability to release silver ions (Ag+ ions) in a prolonged and sustained way. However, negative effects of silver on the patient's cells should not be underestimated. Furthermore, it has been controversially discussed whether AgNP are responsible for nanoparticle-specific outcomes or not. In this study, we investigated the effects of AgNP on human skin keratinocytes (HaCaT) in order to better understand the mechanisms of cytotoxicity and to improve the use of this highly reactive biocide in wound healing. We found that most of the cells with internalized AgNP displayed the typical morphological signs of apoptosis. The cell viability assay (XTT) showed concentration-dependent toxic effects of the AgNP toward HaCaT cells. The generation of reactive oxygen species (ROS) induced by AgNP was investigated in cell suspensions by means of electron paramagnetic resonance (EPR) spectroscopy. In order to distinguish between the effects of Ag+ ions released during AgNP storage and those of Ag+ ions released after nanoparticle application, we compared AgNP stored under air (O2) with AgNP stored under argon (Ar). Dispersions of AgNP stored under Ar have a low content of Ag+ ions because of the absence of oxygen which is needed for oxidative dissolution. The results show that Ag+ ions released during particle storage are responsible for most of the ROS produced during 1 h incubation with the cells. AgNP (Ar) also induced intracellular ROS but to a much smaller extent compared to AgNP (O2). These findings highlight the complexity of experiments to assess the toxicity of AgNP and suggest the possibility of reducing AgNP toxic effects by storing AgNP formulations and even silver-containing wound dressing under an inert gas atmosphere. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.ejpb.2014.07.012
  • 2014 • 98 Iron oxide/polymer-based nanocomposite material for hydrogen sulfide adsorption applications
    Blatt, O. and Helmich, M. and Steuten, B. and Hardt, S. and Bathen, D. and Wiggers, H.
    Chemical Engineering and Technology 37 1938-1944 (2014)
    The processing of iron oxide nanoparticles derived from spray flame synthesis for specific adsorption applications is described. After the as-prepared particles proved the ability for H2S removal in pure gas treatment, two different nanoparticle- based composite materials were prepared. While impregnation of activated carbon with the as-prepared nanoparticles showed the expected increase in H2S adsorption capacities, a significant enhancement in desulfurization performance was observed for a novel iron oxide nanoparticle composite material. H2S adsorption was tested in fixed-bed breakthrough curve measurements. The H2S removal efficiency of the novel material under ambient conditions indicates highly promising properties for potential use in industrial and air pollution control applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ceat.201400303
  • 2014 • 97 Effects of silver nitrate and silver nanoparticles on a planktonic community: General trends after short-term exposure
    Boenigk, J. and Beisser, D. and Zimmermann, S. and Bock, C. and Jakobi, J. and Grabner, D. and Großmann, L. and Rahmann, S. and Barcikowski, S. and Sures, B.
    PLoS ONE 9 (2014)
    Among metal pollutants silver ions are one of the most toxic forms, and have thus been assigned to the highest toxicity class. Its toxicity to a wide range of microorganisms combined with its low toxicity to humans lead to the development of a wealth of silver-based products in many bactericidal applications accounting to more than 1000 nano-technology-based consumer products. Accordingly, silver is a widely distributed metal in the environment originating from its different forms of application as metal, salt and nanoparticle. A realistic assessment of silver nanoparticle toxicity in natural waters is, however, problematic and needs to be linked to experimental approaches. Here we apply metatranscriptome sequencing allowing for elucidating reactions of whole communities present in a water sample to stressors. We compared the toxicity of ionic silver and ligand-free silver nanoparticles by short term exposure on a natural community of aquatic microorganisms. We analyzed the effects of the treatments on metabolic pathways and species composition on the eukaryote metatranscriptome level in order to describe immediate molecular responses of organisms using a community approach. We found significant differences between the samples treated with 5 μg/L AgNO 3 compared to the controls, but no significant differences in the samples treated with AgNP compared to the control samples. Statistical analysis yielded 126 genes (KO-IDs) with significant differential expression with a false discovery rate (FDR) < 0.05 between the control (KO) and AgNO3 (NO3) groups. A KEGG pathway enrichment analysis showed significant results with a FDR below 0.05 for pathways related to photosynthesis. Our study therefore supports the view that ionic silver rather than silver nanoparticles are responsible for silver toxicity. Nevertheless, our results highlight the strength of metatranscriptome approaches for assessing metal toxicity on aquatic communities. © 2014 Boenigk et al.
    view abstractdoi: 10.1371/journal.pone.0095340
  • 2014 • 96 Alloying colloidal silver nanoparticles with gold disproportionally controls antibacterial and toxic effects
    Grade, S. and Eberhard, J. and Jakobi, J. and Winkel, A. and Stiesch, M. and Barcikowski, S.
    Gold Bulletin 47 83-93 (2014)
    Elemental silver nanoparticles are an effective antibacterial substance and are found as additive in various medical applications. Gold nanoparticles are used due to their optical properties in microscopy and cancer therapy. These advantages might be combined within alloyed nanoparticles of both elements and thereby open new fields of interest in research and medical treatment. In this context, laser ablation of solid alloys in liquid gives access to colloidal silver-gold alloy nanoparticles with a homogeneous ultrastructure. Elemental and alloy silver-gold nanoparticles with increasing molar fractions of silver (50, 80, and 100 %) were produced and stabilized with citrate or albumin (BSA). Particles were embedded in agar at concentrations of 3-100 μg cm-3 and tested on clinical relevant Staphylococcus aureus regarding their antibacterial properties. Cytotoxic effects were measured within the same particle concentration range using human gingival fibroblasts (HGFib). As expected, a reduced fraction of silver in the nanoalloys decreased the antibacterial effect on S. aureus according to the evaluated minimal inhibitory concentrations. However, this decrease turned out stronger than expected by its relative mass per particle, due to the electrochemical, disproportionally high effect of gold on the bioresponse to silver within silver-gold nanoalloy particles. BSA was able to stabilize all colloids and maintain antibacterial activity, whereas sodium citrate reduced antibacterial effects and cytotoxicity even at high nanoparticle concentrations. The alloying of silver with gold by laser ablation in liquid produced nanoparticles with both reduced antibacterial and cytotoxic properties in comparison to silver nanoparticles but still retains the application spectrum of both elements combined in one colloid. In particular, alloying with gold may render silver nanoparticles more biocompatible, and allows bioconjugation via established thiol chemistry. © 2013 The Author(s).
    view abstractdoi: 10.1007/s13404-013-0125-6
  • 2014 • 95 Interplay of hydrogen treatment and nitrogen doping in ZnO nanoparticles: A first-principles study
    Gutjahr, J. and Sakong, S. and Kratzer, P.
    Nanotechnology 25 (2014)
    With the help of density functional calculations using the HSE and PBE functionals, it is shown that incorporation of nitrogen into ZnO nanoparticles is energetically less costly compared to ZnO bulk, due to charge transfer between Zn dangling bonds and the NO impurity. Neutral NO results after full passivation of the doped nanoparticles by a treatment with atomic hydrogen. A nanocomposite made from such ZnO particles could show thermally activated p-type hopping conductivity. © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/25/14/145204
  • 2014 • 94 Mimicking exposures to acute and lifetime concentrations of inhaled silver nanoparticles by two different in vitro approaches
    Herzog, F. and Loza, K. and Balog, S. and Clift, M.J.D. and Epple, M. and Gehr, P. and Petri-Fink, A. and Rothen-Rutishauser, B.
    Beilstein Journal of Nanotechnology 5 1357-1370 (2014)
    In the emerging market of nano-sized products, silver nanoparticles (Ag NPs) are widely used due to their antimicrobial properties. Human interaction with Ag NPs can occur through the lung, skin, gastrointestinal tract, and bloodstream. However, the inhalation of Ag NP aerosols is a primary concern. To study the possible effects of inhaled Ag NPs, an in vitro triple cell co-culture model of the human alveolar/airway barrier (A549 epithelial cells, human peripheral blood monocyte derived dendritic and macrophage cells) together with an air-liquid interface cell exposure (ALICE) system was used in order to reflect a real-life exposure scenario. Cells were exposed at the air-liquid interface (ALI) to 0.03, 0.3, and 3 μg Ag/cm2 of Ag NPs (diameter 100 nm; coated with polyvinylpyrrolidone: PVP). Ag NPs were found to be highly aggregated within ALI exposed cells with no impairment of cell morphology. Furthermore, a significant increase in release of cytotoxic (LDH), oxidative stress (SOD-1, HMOX-1) or pro-inflammatory markers (TNF-α, IL-8) was absent. As a comparison, cells were exposed to Ag NPs in submerged conditions to 10, 20, and 30 μg Ag/mL. The deposited dose per surface area was estimated by using a dosimetry model (ISDD) to directly compare submerged vs ALI exposure concentrations after 4 and 24 h. Unlike ALI exposures, the two highest concentrations under submerged conditions promoted a cytotoxic and pro-inflammatory response after 24 h. Interestingly, when cell cultures were co-incubated with lipopolysaccharide (LPS), no synergistic inflammatory effects were observed. By using two different exposure scenarios it has been shown that the ALI as well as the suspension conditions for the lower concentrations after 4 h, reflecting reallife concentrations of an acute 24 h exposure, did not induce any adverse effects in a complex 3D model mimicking the human alveolar/airway barrier. However, the highest concentrations used in the ALI setup, as well as all concentrations under submerged conditions after 24 h, reflecting more of a chronic lifetime exposure concentration, showed cytotoxic as well as pro-inflammatory effects. In conclusion, more studies need to address long-term and chronic Ag NP exposure effects. © 2014 Herzog et al.
    view abstractdoi: 10.3762/bjnano.5.149
  • 2014 • 93 Dose-dependent surface endothelialization and biocompatibility of polyurethane noble metal nanocomposites
    Hess, C. and Schwenke, A. and Wagener, P. and Franzka, S. and Laszlo Sajti, C. and Pflaum, M. and Wiegmann, B. and Haverich, A. and Barcikowski, S.
    Journal of Biomedical Materials Research - Part A 102 1909-1920 (2014)
    Surface pre-endothelialization is a promising approach to improve the hemocompatibility of implants, medical devices, and artificial organs. To promote the adhesive property of thermoplastic polyurethane (TPU) for endothelial cells (ECs), up to 1 wt % of gold (Au) or platinum (Pt) nanoparticles, fabricated by pulsed laser ablation in polymer solution, were embedded into the polymer matrix. The analysis of these nanocomposites showed a homogenous dispersion of the nanoparticles, with average diameters of 7 nm for Au or 9 nm for Pt. A dose-dependent effect was found when ECs were seeded onto nanocomposites comprising different nanoparticle concentrations, resulting in a fivefold improvement of proliferation at 0.1 wt % nanoparticle load. This effect was associated with a nanoparticle concentration-dependent hydrophilicity and negative charge of the nanocomposite. In dynamic flow tests, nanocomposites containing 0.1 wt % Au or Pt nanoparticles allowed for the generation of a confluent and resistant EC layer. Real-time polymerase chain reaction quantification of specific markers for EC activation indicated that ECs cultivated on nanocomposites remain in an inactivated, nonthrombogenic and noninflammatory state; however, maintain the ability to trigger an inflammatory response upon stimulation. These findings were confirmed by a platelet and leukocyte adhesion assay. The results of this study suggest the possible applicability of TPU nanocomposites, containing 0.1 wt % Au or Pt nanoparticles, for the generation of pre-endothelialized surfaces of medical devices. © 2013 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/jbm.a.34860
  • 2014 • 92 Photocatalytic and antimicrobial Ag/ZnO nanocomposites for functionalization of textile fabrics
    Ibǎnescu, M. and Muşat, V. and Textor, T. and Badilita, V. and Mahltig, B.
    Journal of Alloys and Compounds 610 244-249 (2014)
    The utilization of ZnO nanoparticles with photocatalytic and antimicrobial activity for textile treatment has received much attention in recent years. Since silver is a well-known but more expensive antibacterial material, it is of interest to study the extent to which a small amount of silver increases the photocatalytic and antimicrobial activity of the less expensive zinc oxide nanoparticles. This paper reports on the preparation of Ag/ZnO composite nanoparticles by reducing silver on the surface of commercial ZnO nanoparticles dispersed in isopropanol. Crystalline structure, particle size and band gap energy of as-prepared composite nanoparticles were investigated by X-ray diffraction and UV-Vis absorption measurements. Long term stable sols of ZnO and Ag/ZnO nanoparticles were prepared and applied as liquid coating agent for textile treatment, in combination with inorganic-organic hybrid polymer binder sols prepared from the precursors 3-glycidyloxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS). The coating process was carried out on cotton fabrics and cotton/polyester blended fabrics using the pad-dry-cure method. The photocatalytic activity of the nanoparticles, as prepared or applied on textile fabrics, was studied through the degradation of the dye methylene blue (MB) in water under the UV irradiation. The antimicrobial activity of the nanoparticles applied on textile fabrics, was tested against the Gram-negative bacterium Escherichia coli and Gram-positive Micrococcus luteus. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jallcom.2014.04.138
  • 2014 • 91 Correlation of superparamagnetic relaxation with magnetic dipole interaction in capped iron-oxide nanoparticles
    Landers, J. and Stromberg, F. and Darbandi, M. and Schöppner, C. and Keune, W. and Wende, H.
    Journal of Physics Condensed Matter 27 (2014)
    Six nanometer sized iron-oxide nanoparticles capped with an organic surfactant and/or silica shell of various thicknesses have been synthesized by a microemulsion method to enable controllable contributions of interparticle magnetic dipole interaction via tunable interparticle distances. Bare particles with direct surface contact were used as a reference to distinguish between interparticle interaction and surface effects by use of Mössbauer spectroscopy. Superparamagnetic relaxation behaviour was analyzed by SQUID-magnetometry techniques, showing a decrease of the blocking temperature with decreasing interparticle interaction energies kBT 0 obtained by AC susceptibility. A many-state relaxation model enabled us to describe experimental Mössbauer spectra, leading to an effective anisotropy constant Keff ≈ 45 kJm-3 in case of weakly interacting particles, consistent with results from ferromagnetic resonance. Our unique multi-technique approach, spanning a huge regime of characteristic time windows from about 10 s to 5 ns, provides a concise picture of the correlation of superparamagnetic relaxation with interparticle magnetic dipole interaction. © 2015 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/27/2/026002
  • 2014 • 90 Near-field-enhanced, off-resonant laser sintering of semiconductor particles for additive manufacturing of dispersed Au-ZnO-micro/nano hybrid structures
    Lau, M. and Niemann, R.G. and Bartsch, M. and O'Neill, W. and Barcikowski, S.
    Applied Physics A: Materials Science and Processing 114 1023-1030 (2014)
    Off-resonant near-field enhancement by gold nanoparticles adsorbed on crystalline zinc oxide significantly increases the energy efficiency of infrared laser sintering. In detail, ten different gold mass loads on zinc oxide were exposed to 1,064 nm cw-laser radiation. Variation of scan speed, laser power, and spot size showed that the energy threshold required for sintering decreases and sintering process window widens compared to laser sintering of pure zinc oxide powder. Transmission electron microscope analysis after focused ion beam cross sectioning of the sintered particles reveals that supported gold nanoparticles homogenously resolidify in the sintered semiconductor matrix. The enhanced sintering process with ligand-free gold nanoparticles gives access to metal-semiconductor hybrid materials with potential application in light harvesting or energy conversion. © 2014 Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s00339-014-8270-1
  • 2014 • 89 Role and evolution of nanoparticle structure and chemical state during the oxidation of NO over size- and shape-controlled Pt/γ-Al2O 3 catalysts under operando conditions
    Lira, E. and Merte, L.R. and Behafarid, F. and Ono, L.K. and Zhang, L. and Roldan Cuenya, B.
    ACS Catalysis 4 1875-1884 (2014)
    The structure and chemical state of size-selected Pt nanoparticles (NPs) supported on γ-Al2O3 were studied during the oxidation of NO using X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy measurements under operando conditions. The data revealed the formation of PtOx species in the course of the reaction that remained present at the maximum temperature studied, 350 °C. The PtOx species were found in all samples, but those with the smallest NPs showed the highest degree of oxidation. Moreover, NO-induced nanoparticle redispersion was observed at temperatures below 150 °C for all catalysts studied. Catalytic tests showed activity toward the oxidation of NO for all samples. Nevertheless, the catalyst with the smallest NPs was found to be the least active, which is explained by a more extensive formation of PtOx species in this catalyst and their detrimental contribution to the oxidation of NO. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/cs500137r
  • 2014 • 88 A critical evaluation of the interpretation of electrocatalytic nanoimpacts
    Ly, L.S.Y. and Batchelor-Mcauley, C. and Tschulik, K. and Kätelhön, E. and Compton, R.G.
    Journal of Physical Chemistry C 118 17756-17763 (2014)
    The kinetics of the proton reduction reaction is studied on a variety of gold surfaces including both macro (r0 = 1.0 mm) and micro (r 0 = 4.6 μm) electrodes, as well as gold nanoparticles (r NP = ∼10 nm). For the gold nanoparticles, two complementary methodologies of study are used. First the particles are investigated as part of an ensemble response in an array (k0 ∼ 7 × 10-8 m s-1). Second, the rate is recorded stochastically at individually impacting nanoparticles (k0 ∼2 × 10-9 m s -1). This apparent decrease in reaction rates on transitioning from the ensemble to individual nanoparticles is understood in terms of the differing connectivity of the nanoparticles to the electrode surface. During the course of the individual catalytic impacts, or "pulses", the recorded current is found to be highly variable; this variability is interpreted as originating from the nanoscopic motion of the particle above the electrode interface. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp504968j
  • 2014 • 87 Tribolayer formation in a metal-on-metal (MoM) hip joint: An electrochemical investigation
    Mathew, M.T. and Nagelli, C. and Pourzal, R. and Fischer, A. and Laurent, M.P. and Jacobs, J.J. and Wimmer, M.A.
    Journal of the Mechanical Behavior of Biomedical Materials 29 199-212 (2014)
    The demand for total hip replacement (THR) surgery is increasing in the younger population due to faster rehabilitation and more complete restoration of function. Up to 2009, metal-on-metal (MoM) hip joint bearings were a popular choice due to their design flexibility, post-operative stability and relatively low wear rates. The main wear mechanisms that occur along the bearing surface of MoM joints are tribochemical reactions that deposit a mixture of wear debris, metal ions and organic matrix of decomposed proteins known as a tribolayer. No in-depth electrochemical studies have been reported on the structure and characteristics of this tribolayer or about the parameters involved in its formation.In this study, we conducted an electrochemical investigation of different surfaces (bulk-like: control, nano-crystalline: new implant and tribolayer surface: retrieved implant) made out of two commonly used hip CoCrMo alloys (high-carbon and low-carbon). As per ASTM standard, cyclic polarization tests and electrochemical impedance spectroscopy tests were conducted. The results obtained from electrochemical parameters for different surfaces clearly indicated a reduction in corrosion for the tribolayer surface (Icorr: 0.76μA/cm2). Further, polarization resistance (Rp:2.39±0.60MΩ/cm2) and capacitance (Cdl:15.20±0.75μF/cm2) indicated variation in corrosion kinetics for the tribolayer surface, that attributed to its structure and stability in a simulated body environment. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.jmbbm.2013.08.018
  • 2014 • 86 In situ non-DLVO stabilization of surfactant-free, plasmonic gold nanoparticles: Effect of Hofmeister's anions
    Merk, V. and Rehbock, C. and Becker, F. and Hagemann, U. and Nienhaus, H. and Barcikowski, S.
    Langmuir 30 4213-4222 (2014)
    Specific ion effects ranking in the Hofmeister sequence are ubiquitous in biochemical, industrial, and atmospheric processes. In this experimental study specific ion effects inexplicable by the classical DLVO theory have been investigated at curved water-metal interfaces of gold nanoparticles synthesized by a laser ablation process in liquid in the absence of any organic stabilizers. Notably, ion-specific differences in colloidal stability occurred in the Hückel regime at extraordinarily low salinities below 50 μM, and indications of a direct influence of ion-specific effects on the nanoparticle formation process are found. UV-vis, zeta potential, and XPS measurements help to elucidate coagulation properties, electrokinetic potential, and the oxidation state of pristine gold nanoparticles. The results clearly demonstrate that stabilization of ligand-free gold nanoparticles scales proportionally with polarizability and antiproportionally with hydration of anions located at defined positions in a direct Hofmeister sequence of anions. These specific ion effects might be due to the adsorption of chaotropic anions (Br-, SCN-, or I-) at the gold/water interface, leading to repulsive interactions between the partially oxidized gold particles during the nanoparticle formation process. On the other hand, kosmotropic anions (F - or SO4 2-) seem to destabilize the gold colloid, whereas Cl- and NO3 - give rise to an intermediate stability. Quantification of surface charge density indicated that particle stabilization is dominated by ion adsorption and not by surface oxidation. Fundamental insights into specific ion effects on ligand-free aqueous gold nanoparticles beyond purely electrostatic interactions are of paramount importance in biomedical or catalytic applications, since colloidal stability appears to depend greatly on the type of salt rather than on the amount. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/la404556a
  • 2014 • 85 Oxidation of bioethanol using zeolite-encapsulated gold nanoparticles
    Mielby, J. and Abildstrøm, J.O. and Wang, F. and Kasama, T. and Weidenthaler, C. and Kegnæs, S.
    Angewandte Chemie - International Edition 53 12513-12516 (2014)
    With the ongoing developments in biomass conversion, the oxidation of bioethanol to acetaldehyde may become a favorable and green alternative to the preparation from ethylene. Here, a simple and effective method to encapsulate gold nanoparticles in zeolite silicalite-1 is reported and their high activity and selectivity for the catalytic gas-phase oxidation of ethanol are demonstrated. The zeolites are modified by a recrystallization process, which creates intraparticle voids and mesopores that facilitate the formation of small and disperse nanoparticles upon simple impregnation. The individual zeolite crystals comprise a broad range of mesopores and contain up to several hundred gold nanoparticles with a diameter of 2-3 nm that are distributed inside the zeolites rather than on the outer surface. The encapsulated nanoparticles have good stability and result in 50%conversion of ethanol with 98% selectivity toward acetaldehyde at 200°C, which (under the given reaction conditions) corresponds to 606 mol acetaldehyde/mol Au hour-1. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA Weinheim.
    view abstractdoi: 10.1002/anie.201406354
  • 2014 • 84 Interaction of colloidal nanoparticles with their local environment: The (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles
    Pfeiffer, C. and Rehbock, C. and Hühn, D. and Carrillo-Carrion, C. and De Aberasturi, D.J. and Merk, V. and Barcikowski, S. and Parak, W.J.
    Journal of the Royal Society Interface 11 (2014)
    The physico-chemical properties of colloidal nanoparticles (NPs) are influenced by their local environment, as, in turn, the local environment influences the physico-chemical properties of the NPs. In other words, the local environment around NPs has a profound impact on the NPs, and it is different from bulk due to interaction with the NP surface. So far, this important effect has not been addressed in a comprehensive way in the literature. The vicinity of NPs can be sensitively influenced by local ions and ligands, with effects already occurring at extremely low concentrations. NPs in the Hückel regime are more sensitive to fluctuations in the ionic environment, because of a larger Debye length. The local ion concentration hereby affects the colloidal stability of the NPs, as it is different from bulk owing to Debye Hückel screening caused by the charge of the NPs. This can have subtle effects, now caused by the environment to the performance of the NP, such as for example a buffering effect caused by surface reaction on ultrapure ligandfree nanogold, a size quenching effect in the presence of specific ions and a significant impact on fluorophore-labelled NPs acting as ion sensors. Thus, the aim of this review is to clarify and give an unifying view of the complex interplay between the NP's surface with their nanoenvironment. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
    view abstractdoi: 10.1098/rsif.2013.0931
  • 2014 • 83 Biochemical component identification by plasmonic improved whispering gallery mode optical resonance based sensor
    Saetchnikov, V.A. and Tcherniavskaia, E.A. and Saetchnikov, A.V. and Schweiger, G. and Ostendorf, A.
    Proceedings of SPIE - The International Society for Optical Engineering 9126 (2014)
    Experimental data on detection and identification of variety of biochemical agents, such as proteins, microelements, antibiotic of different generation etc. in both single and multi component solutions under varied in wide range concentration analyzed on the light scattering parameters of whispering gallery mode optical resonance based sensor are represented. Multiplexing on parameters and components has been realized using developed fluidic sensor cell with fixed in adhesive layer dielectric microspheres and data processing. Biochemical component identification has been performed by developed network analysis techniques. Developed approach is demonstrated to be applicable both for single agent and for multi component biochemical analysis. Novel technique based on optical resonance on microring structures, plasmon resonance and identification tools has been developed. To improve a sensitivity of microring structures microspheres fixed by adhesive had been treated previously by gold nanoparticle solution. Another technique used thin film gold layers deposited on the substrate below adhesive. Both biomolecule and nanoparticle injections caused considerable changes of optical resonance spectra. Plasmonic gold layers under optimized thickness also improve parameters of optical resonance spectra. Biochemical component identification has been also performed by developed network analysis techniques both for single and for multi component solution. So advantages of plasmon enhancing optical microcavity resonance with multiparameter identification tools is used for development of a new platform for ultra sensitive label-free biomedical sensor. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2051486
  • 2014 • 82 Two-color SERS microscopy for protein co-localization in prostate tissue with primary antibody-protein A/G-gold nanocluster conjugates
    Salehi, M. and Schneider, L. and Ströbel, P. and Marx, A. and Packeisen, J. and Schlücker, S.
    Nanoscale 6 2361-2367 (2014)
    SERS microscopy is a novel staining technique in immunohistochemistry, which is based on antibodies labeled with functionalized noble metal colloids called SERS labels or nanotags for optical detection. Conventional covalent bioconjugation of these SERS labels cannot prevent blocking of the antigen recognition sites of the antibody. We present a rational chemical design for SERS label-antibody conjugates which addresses this issue. Highly sensitive, silica-coated gold nanoparticle clusters as SERS labels are non-covalently conjugated to primary antibodies by using the chimeric protein A/G, which selectively recognizes the Fc part of antibodies and therefore prevents blocking of the antigen recognition sites. In proof-of-concept two-color imaging experiments for the co-localization of p63 and PSA on non-neoplastic prostate tissue FFPE specimens, we demonstrate the specificity and signal brightness of these rationally designed primary antibody-protein A/G-gold nanocluster conjugates. © 2014 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3nr05890e
  • 2014 • 81 Plasmonic and photonic scattering and near fields of nanoparticles
    Schmid, M. and Andrae, P. and Manley, P.
    Nanoscale Research Letters 9 1-11 (2014)
    We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell's equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results. © 2014 Schmid et al.
    view abstractdoi: 10.1186/1556-276X-9-50
  • 2014 • 80 Targeted manipulation of metal-organic frameworks to direct sorption properties
    Schneemann, A. and Henke, S. and Schwedler, I. and Fischer, R.A.
    ChemPhysChem 15 823-839 (2014)
    Metal-organic frameworks are promising materials for manifold applications. This Minireview highlights approaches for the fine-tuning of specific sorption properties (e.g. capacity, selectivity, and breathing behavior) of this interesting class of materials. Central aspects covered are the control over the crystal morphology, the targeted tuning of sorption properties by judicious choice of metal centers and linkers, and the preparation of host-guest systems. We want to introduce the reader to these topics on the basis of the manipulation of a handful of outstanding prototypical metal-organic frameworks. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.201300976
  • 2014 • 79 Effect of silver nanoparticles on human mesenchymal stem cell differentiation
    Sengstock, C. and Diendorf, J. and Epple, M. and Schildhauer, T.A. and Köller, M.
    Beilstein Journal of Nanotechnology 5 2058-2069 (2014)
    Background: Silver nanoparticles (Ag-NP) are one of the fastest growing products in nano-medicine due to their enhanced antibacterial activity at the nanoscale level. In biomedicine, hundreds of products have been coated with Ag-NP. For example, various medical devices include silver, such as surgical instruments, bone implants and wound dressings. After the degradation of these materials, or depending on the coating technique, silver in nanoparticle or ion form can be released and may come into close contact with tissues and cells. Despite incorporation of Ag-NP as an antibacterial agent in different products, the toxicological and biological effects of silver in the human body after long-term and low-concentration exposure are not well understood. In the current study, we investigated the effects of both ionic and nanoparticulate silver on the differentiation of human mesenchymal stem cells (hMSCs) into adipogenic, osteogenic and chondrogenic lineages and on the secretion of the respective differentiation markers adiponectin, osteocalcin and aggrecan. Results: As shown through laser scanning microscopy, Ag-NP with a size of 80 nm (hydrodynamic diameter) were taken up into hMSCs as nanoparticulate material. After 24 h of incubation, these Ag-NP were mainly found in the endo-lysosomal cell compartment as agglomerated material. Cytotoxicity was observed for differentiated or undifferentiated hMSCs treated with high silver concentrations (≥20 μg·mL-1 Ag-NP; ≥1.5 μg·mL-1 Ag+ ions) but not with low-concentration treatments (≤10 μg·mL-1 Ag-NP; ≤1.0 μg·mL-1 Ag+ ions). Subtoxic concentrations of Ag-NP and Ag+ ions impaired the adipogenic and osteogenic differentiation of hMSCs in a concentration-dependent manner, whereas chondrogenic differentiation was unaffected after 21 d of incubation. In contrast to aggrecan, the inhibitory effect of adipogenic and osteogenic differentiation was confirmed by a decrease in the secretion of specific biomarkers, including adiponectin (adipocytes) and osteocalcin (osteoblasts). Conclusion: Aside from the well-studied antibacterial effect of silver, little is known about the influence of nano-silver on cell differentiation processes. Our results demonstrate that ionic or nanoparticulate silver attenuates the adipogenic and osteogenic differentiation of hMSCs even at non-toxic concentrations. Therefore, more studies are needed to investigate the effects of silver species on cells at low concentrations during long-term treatment. © 2014 Sengstock et al.
    view abstractdoi: 10.3762/bjnano.5.214
  • 2014 • 78 Gold nanoparticles interfere with sperm functionality by membrane adsorption without penetration
    Taylor, U. and Barchanski, A. and Petersen, S. and Kues, W.A. and Baulain, U. and Gamrad, L. and Sajti, L. and Barcikowski, S. and Rath, D.
    Nanotoxicology 8 118-127 (2014)
    To examine gold nanoparticle reprotoxicity, bovine spermatozoa were challenged with ligand-free or oligonucleotide-conjugated gold nanoparticles synthesized purely without any surfactants by laser ablation. Sperm motility declined at nanoparticle mass dose of 10 μg/ml (corresponding to ∼14 000 nanoparticles per sperm cell) regardless of surface modification. Sperm morphology and viability remained unimpaired at all concentrations. Transmission electron microscopy showed an modification dependant attachment of nanoparticles to the cell membrane of spermatozoa, but provided no evidence for nanoparticle entrance into sperm cells. A molecular examination revealed a reduction of free thiol residues on the cell membrane after nanoparticle exposure, which could explain the decrease in sperm motility. Sperm fertilising ability decreased after exposure to 10 μg/ml of ligand-free nanoparticles indicating that agglomerated ligand-free nanoparticles interfere with membrane properties necessary for fertilisation. In conclusion, nanoparticles may impair key sperm functions solely by interacting with the sperm surface membrane. © 2014 Informa UK Ltd. All rights reserved.
    view abstractdoi: 10.3109/17435390.2013.859321
  • 2014 • 77 Rational design of gold nanoparticle toxicology assays: A question of exposure scenario, dose and experimental setup
    Taylor, U. and Rehbock, C. and Streich, C. and Rath, D. and Barcikowski, S.
    Nanomedicine 9 1971-1989 (2014)
    Many studies have evaluated the toxicity of gold nanoparticles, although reliable predictions based on these results are rare. In order to overcome this problem, this article highlights strategies to improve comparability and standardization of nanotoxicological studies. To this end, it is proposed that we should adapt the nanomaterial to the addressed exposure scenario, using ligand-free nanoparticle references in order to differentiate ligand effects from size effects. Furthermore, surface-weighted particle dosing referenced to the biologically relevant parameter (e.g., cell number or organ mass) is proposed as the gold standard. In addition, it is recommended that we should shift the focus of toxicological experiments from 'live-dead' assays to the assessment of cell function, as this strategy allows observation of bioresponses at lower doses that are more relevant for in vivo scenarios. © 2014 Future Medicine Ltd.
    view abstractdoi: 10.2217/nnm.14.139
  • 2014 • 76 Reprotoxicity of gold, silver, and gold-silver alloy nanoparticles on mammalian gametes
    Tiedemann, D. and Taylor, U. and Rehbock, C. and Jakobi, J. and Klein, S. and Kues, W.A. and Barcikowski, S. and Rath, D.
    Analyst 139 931-942 (2014)
    Metal and alloy nanoparticles are increasingly developed for biomedical applications, while a firm understanding of their biocompatibility is still missing. Various properties have been reported to influence the toxic potential of nanoparticles. This study aimed to assess the impact of nanoparticle size, surface ligands and chemical composition of gold, silver or gold-silver alloy nanoparticles on mammalian gametes. An in vitro assay for porcine gametes was developed, since these are delicate primary cells, for which well-established culture systems exist and functional parameters are defined. During coincubation with oocytes for 46 h neither any of the tested gold nanoparticles nor the gold-silver alloy particles with a silver molar fraction of up to 50% showed any impact on oocyte maturation. Alloy nanoparticles with 80% silver molar fraction and pure silver nanoparticles inhibited cumulus-oocyte maturation. Confocal microscopy revealed a selective uptake of gold nanoparticles by oocytes, while silver and alloy particles mainly accumulated in the cumulus cell layer surrounding the oocyte. Interestingly sperm vitality parameters (motility, membrane integrity and morphology) were not affected by any of the tested nanoparticles. Only sporadic association of nanoparticles with the sperm plasma membrane was found by transmission electron microscopy. In conclusion, mammalian oocytes were sensitive to silver containing nanoparticles. Likely, the delicate process of completing meiosis in maternal gametes features high vulnerability towards nanomaterial derived toxicity. The results imply that released Ag +-ions are responsible for the observed toxicity, but the compounding into an alloy seemed to alleviate the toxic effects to a certain extent. This journal is © The Royal Society of Chemistry 2014.
    view abstractdoi: 10.1039/c3an01463k
  • 2014 • 75 A proof-of-concept - Using pre-created nucleation centres to improve the limit of detection in anodic stripping voltammetry
    Toh, H.S. and Batchelor-Mcauley, C. and Tschulik, K. and Damm, C. and Compton, R.G.
    Sensors and Actuators, B: Chemical 193 315-319 (2014)
    Anodic stripping voltammetry is a much-utilised method for trace metal analysis. We provide a simple proof-of-concept technique to improve the sensitivity of the method, which is illustrated by the detection of silver cations. This approach requires an electrode pre-treatment, which involves drop casting a metal nanoparticle suspension and oxidising the nanoparticles, leaving small metal nuclei on the electrode surface. In turn, the small metal nuclei act as nucleation sites for subsequent metal deposition when used to interrogate target solutions. In particular, the pre-treatment increases the amount of deposited metal in a given amount of time. Silver nitrate concentrations from 30 nM to 1 μM were tested and at silver ion concentration of 300 nM, the pre-treated electrode gave a signal, which was 40 times larger than the untreated electrode. The larger signal leads to the enhancement of sensitivity and a lowering of the detection limit of anodic stripping voltammetry without introducing other organic molecules, metals or impurities. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.snb.2013.11.120
  • 2014 • 74 Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural
    Wang, G.-H. and Hilgert, J. and Richter, F.H. and Wang, F. and Bongard, H.-J. and Spliethoff, B. and Weidenthaler, C. and Schüth, F.
    Nature Materials 13 293-300 (2014)
    The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diameters of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres. © 2014 Macmillan Publishers Limited.
    view abstractdoi: 10.1038/nmat3872
  • 2014 • 73 Evaluation of pulsed laser ablation in liquids generated gold nanoparticles as novel transfection tools: Efficiency and cytotoxicity
    Willenbrock, S. and Durán, M.C. and Barchanski, A. and Barcikowski, S. and Feige, K. and Nolte, I. and Murua Escobar, H.
    Proceedings of SPIE - The International Society for Optical Engineering 8972 (2014)
    Varying transfection efficiencies and cytotoxicity are crucial aspects in cell manipulation. The utilization of gold nanoparticles (AuNP) has lately attracted special interest to enhance transfection efficiency. Conventional AuNP are usually generated by chemical reactions or gas pyrolysis requiring often cell-toxic stabilizers or coatings to conserve their characteristics. Alternatively, stabilizer- and coating-free, highly pure, colloidal AuNP can be generated by pulsed laser ablation in liquids (PLAL). Mammalian cells were transfected efficiently by addition of PLAL-AuNP, but data systematically evaluating the cell-toxic potential are lacking. Herein, the transfection efficiency and cytotoxicity of PLAL AuNP was evaluated by transfection of a mammalian cell line with a recombinant HMGB1/GFP DNA expression vector. Different methods were compared using two sizes of PLAL-AuNP, commercialized AuNP, two magnetic NP-based protocols and a conventional transfection reagent (FuGENE HD; FHD). PLAL-AuNP were generated using a Spitfire Pro femtosecond laser system delivering 120 fs laser pulses at a wavelength of 800 nm focusing the fs-laser beam on a 99.99% pure gold target placed in ddH2O. Transfection efficiencies were analyzed after 24h using fluorescence microscopy and flow cytometry. Toxicity was assessed measuring cell proliferation and percentage of necrotic, propidium iodide positive cells (PI %). The addition of PLAL-AuNP significantly enhanced transfection efficiencies (FHD: 31 %; PLAL-AuNP size-1: 46 %; size-2: 50 %) with increased PI% but no reduced cell proliferation. Commercial AuNP-transfection showed significantly lower efficiency (23 %), slightly increased PI % and reduced cell proliferation. Magnetic NP based methods were less effective but showing also lowest cytotoxicity. In conclusion, addition of PLAL-AuNP provides a novel tool for transfection efficiency enhancement with acceptable cytotoxic side-effects. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2038453
  • 2014 • 72 Gold and silver nanoparticle monomers are non-SERS-active: A negative experimental study with silica-encapsulated Raman-reporter-coated metal colloids
    Zhang, Y. and Walkenfort, B. and Yoon, J.H. and Schlücker, S. and Xie, W.
    Physical Chemistry Chemical Physics 17 21120-21126 (2014)
    Noble metal nanoparticles (NPs) are the most commonly employed plasmonic substrates in surface-enhanced Raman scattering (SERS) experiments. Computer simulations show that monomers of Ag and Au nanocrystals ("spherical" NPs) do not exhibit a notable plasmonic enhancement, i.e., they are essentially non-SERS-active. However, in experiments, SERS enhanced by spherical NP colloids has been frequently reported. This implies that the monomers do not have strong SERS activity, but detectable enhancement should more or less be there. Because of the gap between theory and practice, it is important to demonstrate experimentally how SERS-active the metal colloid actually is and, in case a SERS signal is observed, where it originates from. In particular the aggregation of the colloid, induced by high centrifugal forces in washing steps or due to a harsh ionic environment of the suspension medium, should be controlled since it is the very high SERS activity of NP clusters which dominates the overall SERS signal of the colloid. We report here the experimental evaluation of the SERS activity of 80 nm Au and Ag NP monomers. Instead of showing fancy nanostructures and super SERS enhancement, we present the method on how to obtain negative experimental data. In this approach, no SERS signal was obtained from the colloid with a Raman reporter on the metal surface when the NPs were encapsulated carefully within a thick silica shell. Without silica encapsulation, if a very low centrifugation speed is used for the washing steps, only a negligible SERS signal can be detected even at very high NP concentrations. In contrast, strong SERS signals can be detected when the NPs are suspended in acidic solutions. These results indicate that Au and Ag NP monomers essentially exhibit no SERS activity of practical relevance. © the Owner Societies 2015.
    view abstractdoi: 10.1039/c4cp05073h
  • 2014 • 71 Oxygen-deficient titania as alternative support for Pt catalysts for the oxygen reduction reaction
    Zhao, A. and Masa, J. and Xia, W.
    Journal of Energy Chemistry 23 701-707 (2014)
    Insufficient electrochemical stability is a major challenge for carbon materials in oxygen reduction reaction (ORR) due to carbon corrosion and insufficient metal-support interactions. In this work, titania is explored as an alternative support for Pt catalysts. Oxygen deficient titania samples including TiO<inf>2-x</inf> and TiO<inf>2-x</inf>N<inf>y</inf> were obtained by thermal treatment of anatase TiO<inf>2</inf> under flowing H<inf>2</inf> and NH<inf>3</inf>, respectively. Pt nanoparticles were deposited on the titania by a modified ethylene glycol method. The samples were characterized by N<inf>2</inf>-physisorption, X-ray diffraction and X-ray photoelectron spectroscopy. The ORR activity and long-term stability of supported Pt catalysts were evaluated using linear sweep voltammetry and chronoamperometry in 0.1 mol/L HClO<inf>4</inf>. Pt/TiO<inf>2-x</inf> and Pt/TiO<inf>2-x</inf>N<inf>y</inf> showed higher ORR activities than Pt/TiO<inf>2</inf> as indicated by higher onset potentials. Oxygen deficiency in TiO<inf>2-x</inf> and TiO<inf>2-x</inf>N<inf>y</inf> contributed to the high ORR activity due to enhanced charge transfer, as disclosed by electrochemical impedance spectroscopy studies. Electrochemical stability studies revealed that Pt/TiO<inf>2-x</inf> exhibited a higher stability with a lower current decay rate than commercial Pt/C, which can be attributed to the stable oxide support and strong interaction between Pt nanoparticles and the oxygen-deficient TiO<inf>2-x</inf> support. © 2014 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/S2095-4956(14)60202-3
  • 2013 • 70 Silver as antibacterial agent: Ion, nanoparticle, and metal
    Chernousova, S. and Epple, M.
    Angewandte Chemie - International Edition 52 1636-1653 (2013)
    The antibacterial action of silver is utilized in numerous consumer products and medical devices. Metallic silver, silver salts, and also silver nanoparticles are used for this purpose. The state of research on the effect of silver on bacteria, cells, and higher organisms is summarized. It can be concluded that the therapeutic window for silver is narrower than often assumed. However, the risks for humans and the environment are probably limited. Silver shield: Silver is used in different forms as an antibacterial agent. Earlier, sparingly soluble silver salts were predominantly used, but today, silver nanoparticles (see picture for an SEM image of cubic silver nanoparticles) are gaining increasing importance. As silver is also toxic towards mammalian cells, there is the question of the therapeutic window in the cases of consumer products and medical devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201205923
  • 2013 • 69 Size control of gold nanoparticles during laser ablation in liquids with different functional molecules
    Essaidi, A. and Chakif, M. and Schöps, B. and Aumman, A. and Xiao, S. and Esen, C. and Ostendorf, A.
    Journal of Laser Micro Nanoengineering 8 131-136 (2013)
    Over the last decade many papers dedicated to the generation of nanoparticles in liquids using la-ser ablation have been published. They have shown that the nanoparticles size distribution is de-pendent of the laser fluence and shifts towards smaller sizes when the surfactant concentration is in-creased. In this paper an alternative approach is presented that permits the control of the size distri-bution of gold nanoparticles during laser ablation in aqueous solutions containing different surfactant molecules with different shapes and size.
    view abstractdoi: 10.2961/jlmn.2013.02.0003
  • 2013 • 68 Long-term active antimicrobial coatings for surgical sutures based on silver nanoparticles and hyperbranched polylysine
    Ho, C.H. and Odermatt, E.K. and Berndt, I. and Tiller, J.C.
    Journal of Biomaterials Science, Polymer Edition 24 1589-1600 (2013)
    The goal of this study was to develop a long-term active antimicrobial coating for surgical sutures. To this end, two water-insoluble polymeric nanocontainers based on hyperbranched polylysine (HPL), hydrophobically modified by either using glycidyl hexadecyl ether, or a mixture of stearoyl/palmitoyl chloride, were synthesized. Highly stabilized silver nanoparticles (AgNPs, 2-5 nm in size) were generated by dissolving silver nitrate in the modified HPL solutions in toluene followed by reduction with L-ascorbic acid. Poly(glycolic acid)-based surgical sutures were dip-coated with the two different polymeric silver nanocomposites. The coated sutures showed high efficacies of more than 99.5% reduction of adhesion of living Staphylococcus aureus cells onto the surface compared to the uncoated specimen. Silver release experiments were performed on the HPL-AgNP modified sutures by washing them in phosphate buffered saline for a period of 30 days. These coatings showed a constant release of silver ions over more than 30 days. After this period of washing, the sutures retained their high efficacies against bacterial adhesion. Cytotoxicity tests using L929 mouse fibroblast cells showed that the materials are basically non-cytotoxic. © 2013 Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/09205063.2013.782803
  • 2013 • 67 Facile synthesis of polymer core@silver shell hybrid nanoparticles with super surface enhanced Raman scattering capability
    Huo, D. and He, J. and Yang, S. and Zhou, Z. and Hu, Y. and Epple, M.
    Journal of Colloid and Interface Science 393 119-125 (2013)
    Silver nano-shells (SNSs) were synthesized via a two-step seeds-mediated method. Polymer cores were composed of ultrafine gold nanoparticles (NPs) modified chitosan-poly(acrylic acid) nanoparticles (CS-PAA NPs). Then, deposition of silver upon gold nucleus leads to the seed enlargement and finally forms silver shell on the surface of CS-PAA NPs to get SNSs. Transmission electron microscope (TEM) showed SNSs had a discrete silver shell plus some pores and gaps, which could acted as "hot spots" and provided the great potential of these SNSs to be used as SERS substrates with wavelength ranging from visible to infrared region (700-1000. nm) by tuning shell coverage of silver. SERS experiments with dibenzyl disulphide (DBDS) as the indicator showed that the resulting SNSs allowed the production of highly consistent enhancement of the Raman signals down to nM concentrations of DBDS. Considering the excellent biocompatibility of polymer core and their small size, these SNSs are highly desirable candidates as the enhancers for high performance SERS analysis and as SERS optical labels in biomedical imaging. © 2012 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2012.11.003
  • 2013 • 66 Correlation of electronic and magnetic properties of thin polymer layers with cobalt nanoparticles
    Kharchenko, A. and Lukashevich, M. and Popok, V. and Khaibullin, R. and Valeev, V. and Bazarov, V. and Petracic, O. and Wieck, A. and Odzhaev, V.
    Particle and Particle Systems Characterization 30 180-184 (2013)
    Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co+ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non-monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin-dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 1017 cm-2) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs. Nanoparticles of cobalt are synthesized in shallow layers of polyimide using low-energy implantation of cobalt ions. Nucleation of individual particles and their percolation are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites. By tuning the implantation regimes magnetoresistance and transitions between the superparamagnetic and ferromagnenic behavior can be controlled. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppsc.201200042
  • 2013 • 65 Nanoparticle-mediated gene transfer from electrophoretically coated metal surfaces
    Kovtun, A. and Neumann, S. and Neumeier, M. and Urch, H. and Heumann, R. and Gepp, M.M. and Wallat, K. and Koeller, M. and Zimmermann, H. and Epple, M.
    Journal of Physical Chemistry B 117 1550-1555 (2013)
    The transfer of genetic information into living cells is a powerful tool to manipulate their protein expression by the regulation of protein synthesis. This can be used for the treatment of genetically caused diseases (gene therapy). However, the systemic application of genes is associated with a number of problems, such as a targeted gene delivery and potential side effects. Here we present a method for the spatial application of nanoparticle-based gene therapy. Titanium was electrophoretically coated with DNA-functionalized calcium phosphate nanoparticles. NIH3T3 cells and HeLa cells were transfected with pcDNA3-EGFP. We monitored the transfection in vitro by fluorescence microscopy, flow cytometry, and Western Blot analysis. By coating a transparent substrate, i.e., indium tin oxide (ITO), with nanoparticles, we followed the transfection by live cell imaging. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/jp303448v
  • 2013 • 64 Evidence for metal-support interactions in Au modified TiO x/SBA-15 materials prepared by photodeposition
    Mei, B. and Wiktor, C. and Turner, S. and Pougin, A. and Van Tendeloo, G. and Fischer, R.A. and Muhler, M. and Strunk, J.
    ACS Catalysis 3 3041-3049 (2013)
    Gold nanoparticles have been efficiently photodeposited onto titanate-loaded SBA-15 (Ti(x)/SBA-15) with different titania coordination. Transmission electron microscopy shows that relatively large Au nanoparticles are photodeposited on the outer surface of the Ti(x)/SBA-15 materials and that TiOx tends to form agglomerates in close proximity to the Au nanoparticles, often forming core-shell Au/TiOx structures. This behavior resembles typical processes observed due to strong-metal support interactions. In the presence of gold, the formation of hydrogen on Ti(x)/SBA-15 during the photodeposition process and the performance in the hydroxylation of terephthalic acid is greatly enhanced. The activity of the Au/Ti(x)/SBA-15 materials is found to depend on the TiOx loading, increasing with a larger amount of initially isolated TiO4 tetrahedra. Samples with initially clustered TiOx species show lower photocatalytic activities. When isolated zinc oxide (ZnOx) species are present on Ti(x)/SBA-15, gold nanoparticles are smaller and well dispersed within the pores. Agglomeration of TiOx species and the formation of Au/TiO x structures is negligible. The dispersion of gold and the formation of Au/TiOx in the SBA-15 matrix seem to depend on the mobility of the TiOx species. The mobility is determined by the initial degree of agglomeration of TiOx. Effective hydrogen evolution requires Au/TiOx core-shell composites as in Au/Ti(x)/SBA-15, whereas hydroxylation of terephthalic acid can also be performed with Au/ZnO x/TiOx/SBA-15 materials. However, isolated TiOx species have to be grafted onto the support prior to the zinc oxide species, providing strong evidence for the necessity of Ti-O-Si bridges for high photocatalytic activity in terephthalic acid hydroxylation. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/cs400964k
  • 2013 • 63 Silver-doped calcium phosphate nanoparticles: Synthesis, characterization, and toxic effects toward mammalian and prokaryotic cells
    Peetsch, A. and Greulich, C. and Braun, D. and Stroetges, C. and Rehage, H. and Siebers, B. and Köller, M. and Epple, M.
    Colloids and Surfaces B: Biointerfaces 102 724-729 (2013)
    Spherical silver-doped calcium phosphate nanoparticles were synthesized in a co-precipitation route from calcium nitrate/silver nitrate and ammonium phosphate in a continuous process and colloidally stabilized by carboxymethyl cellulose. Nanoparticles with 0.39wt% silver content and a diameter of about 50-60nm were obtained. The toxic effects toward mammalian and prokaryotic cells were determined by viability tests and determination of the minimal inhibitory and minimal bactericidal concentrations (MIC and MBC). Three mammalian cells lines, i.e. human mesenchymal stem cells (hMSC) and blood peripheral mononuclear cells (PBMC, monocytes and T-lymphocytes), and two prokaryotic strains, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used. Silver-doped calcium phosphate nanoparticles and silver acetate showed similar effect toward mammalian and prokaryotic cells with toxic silver concentrations in the range of 1-3μgmL-1. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2012.09.040
  • 2013 • 62 Sex selection of sperm in farm animals: Status report and developmental prospects
    Rath, D. and Barcikowski, S. and Graaf, S.D. and Garrels, W. and Grossfeld, R. and Klein, S. and Knabe, W. and Knorr, C. and Kues, W. and Meyer, H. and Michl, J. and Moench-Tegeder, G. and Rehbock, C. and Taylor, U. and Washausen, S.
    Reproduction 145 R15-R30 (2013)
    Pre-selection of spermatozoa based on the relative DNA difference between X- and Y-chromosome bearing populations by flow cytometry is an established method that has been introduced into commercial cattle production. Although several important improvements have increased the sort efficiency, the fertilising ability of sexed spermatozoa based on offspring per insemination is still behind farmers' expectations. The main stress factors, especially on mitochondria, that reduce the lifespan of spermatozoa are described, and new technical as well as biological solutions to maintain the natural sperm integrity and to increase the sorting efficiency are discussed. Among these methods are the identification of Y-chromosome bearing spermatozoa by bi-functionalised gold nanoparticles and triplex hybridisation in vivo as well as new laser-controlled deflection system that replaces the deflection of spermatozoa in the electrostatic field. Additionally, as well as a new nonsurgical transfer system of spermatozoa into the oviduct of cows has been developed and allows a significant reduction of spermatozoa per transfer. Altogether, the improvements made in the recent years will allow a broader use of sex-sorted spermatozoa even in those species that require more cells than cows and sheep. © 2013 Society for Reproduction and Fertility.
    view abstractdoi: 10.1530/REP-12-0151
  • 2013 • 61 Size control of laser-fabricated surfactant-free gold nanoparticles with highly diluted electrolytes and their subsequent bioconjugation
    Rehbock, C. and Merk, V. and Gamrad, L. and Streubel, R. and Barcikowski, S.
    Physical Chemistry Chemical Physics 15 3057-3067 (2013)
    Size control of laser-fabricated surfactant-free gold nanoparticles is a challenging endeavor. In this work, we show that size control can be achieved by adding ions with low salinity during synthesis. In addition, this approach offers the opportunity to fundamentally study ion interactions with bare nanoparticle surfaces and can help to elucidate the nanoparticle formation mechanism. The studies were carried out in a flow-through reactor and in the presence of NaCl, NaBr and sodium phosphate buffer at minimal ionic strengths. A significant size quenching effect at ionic strengths from 1-50 μM was found, which allowed surfactant-free nanoparticle size control with average diameters of 6-30 nm. This effect went along with low polydispersity and minimal aggregation tendencies and was confirmed by UV-vis spectroscopy, TEM, SEM and analytical disk centrifugation. Our findings indicate that size quenching originates from an anionic electrostatic stabilization depending on the nanoparticle surface area, which may be caused by specific ion adsorption. By subsequent delayed bioconjugation in liquid-flow using bovine serum albumin as a stabilizing agent, nano-bioconjugates with good stability in cell culture media were obtained, which are applicable in toxicology and cell biology. This journal is © 2013 the Owner Societies.
    view abstractdoi: 10.1039/c2cp42641b
  • 2013 • 60 Rapid immuno-SERS microscopy for tissue imaging with single-nanoparticle sensitivity
    Salehi, M. and Steinigeweg, D. and Ströbel, P. and Marx, A. and Packeisen, J. and Schlücker, S.
    Journal of Biophotonics 6 785-792 (2013)
    Immuno-SERS microscopy is a novel imaging technique in nano-biophotonics, which employs antibodies labeled with SERS-active nanoparticles in conjunction with Raman microscopy. Rapid data acquisition is of central importance for screening large areas of tissue specimens. Here, we first discuss the role of SERS labels with single-particle sensitivity in immuno-SERS microscopy, in particular with respect to false-negative results. In combined single-particle experiments (SERS microscopy/dark-field microscopy/HR-SEM), we then demonstrate that small glass-coated clusters (dimers and trimers) of gold nanospheres exhibit the desired single-particle SERS sensitivity, even at acquisition times as short as 30 msec per pixel, while monomers do not. The proof-of-concept for rapid immuno-SERS microscopy with 30 msec acquisition time per pixel for selective imaging of the p53 family member p63 in prostate tissue sections is demonstrated. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/jbio.201200148
  • 2013 • 59 Scanning near-field optical microscopy on dense random assemblies of metal nanoparticles
    Schmid, M. and Grandidier, J. and Atwater, H.A.
    Journal of Optics (United Kingdom) 15 (2013)
    Plasmonic absorption enhancement by metal nanoparticles strongly relies on the local electric field distributions generated by the nanoparticles. Therefore, here we study random assemblies of metal nanoparticles as they are widely considered for solar cell application with scanning near-field optical microscopy. A collective scattering behavior is observed despite a resolution on the particle size. We find variations in scattering intensity on a length scale several times larger than in the topography. FDTD (finite-difference time domain) simulations show the impact of irregularities and size variations on the scattering behavior. An understanding of the plasmonic scattering behavior at the nanometer scale will support the successful application of nanoparticles for absorption enhancement in thin-film solar cells. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/2040-8978/15/12/125001
  • 2013 • 58 Stability of plasmonic metal nanoparticles integrated in the back contact of ultra-thin Cu(In,Ga)S2 solar cells
    Schmid, M. and Klaer, J. and Klenk, R. and Topič, M. and Krč, J.
    Thin Solid Films 527 308-313 (2013)
    Ultra-thin solar cells on transparent back contacts constitute the basis for highly efficient tandem solar devices which can surpass the single cell efficiency limit. The material reduction related to ultra-thin high efficiency devices additionally lowers the price. Despite the fact that they are ultra-thin the absorbers still have to remain optically thick and therefore require adequate light management. A promising approach for enhanced absorption is plasmonic scattering from metal nanoparticles. In this paper we discuss the experimental incorporation of Ag nanoparticles in ultra-thin wide-gap chalcopyrite solar cells on transparent back contacts. A 6.9% efficient 500 nm Cu(In,Ga)S2 solar cell on In2O3:Mo (at this point without nanoparticles) is the starting point. For the predicted optimum design of including particles at the rear side the stability of the nanostructures integrated in the back contact is investigated in detail. As a first step towards proof-of-concept, absorption enhancement from the nanoparticles included in the complete solar cell is experimentally shown in optical properties. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2012.12.023
  • 2013 • 57 Adjustment and online determination of primary particle size in transferred arc synthesis of copper nanoparticles
    Stein, M. and Kiesler, D. and Kruis, F.E.
    Aerosol Science and Technology 47 1276-1284 (2013)
    Scaling up metal nanoparticle production is a desired goal of much research, the need of the industry due to the growing market of applications increases significantly. However, a scale up of production rate often leads to an increase in particle size and a broadening of size distribution. Particle characterization in terms of size is mostly done after synthesis. In this work, a transferred arc process is optimized to increase the production rate of pure copper nanoparticles economically. The maximum production rate for different particle sizes is determined by TEOM measurements. While the influence of different carrier gases has been investigated before, different mixtures of nitrogen and argon as carrier gas are used to manipulate the primary particle size. Primary particle size determination is performed by a novel analysis method based on parallel online ELPI and SMPS measurement. An equation is found to calculate the mass mobility exponent directly on the basis of the effective density of an agglomerate. Hence, the method is suitable for determining the primary particle sizes directly online. Copyright © American Association for Aerosol Research.
    view abstractdoi: 10.1080/02786826.2013.835484
  • 2013 • 56 Effect of carrier gas composition on transferred arc metal nanoparticle synthesis
    Stein, M. and Kiesler, D. and Kruis, F.E.
    Journal of Nanoparticle Research 15 (2013)
    Metal nanoparticles are used in a great number of applications; an effective and economical production scaling-up is hence desirable. A simple and cost-effective transferred arc process is developed, which produces pure metal (Zn, Cu, and Ag) nanoparticles with high production rates, while allowing fast optimization based on energy efficiency. Different carrier gas compositions, as well as the electrode arrangements and the power input are investigated to improve the production and its efficiency and to understand the arc production behavior. The production rates are determined by a novel process monitoring method, which combines an online microbalance method with a scanning mobility particle sizer for fast production rate and size distribution measurement. Particle characterization is performed via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction measurements. It is found that the carrier gas composition has the largest impact on the particle production rate and can increase it with orders of magnitude. This appears to be not only a result of the increased heat flux and melt temperature but also of the formation of tiny nitrogen (hydrogen) bubbles in the molten feedstock, which impacts feedstock evaporation significantly in bi-atomic gases. A production rate of sub 200 nm particles from 20 up to 2,500 mg/h has been realized for the different metals. In this production range, specific power consumptions as low as 0.08 kWh/g have been reached. © 2013 Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11051-012-1400-9
  • 2013 • 55 Single gold trimers and 3D superstructures exhibit a polarization- independent SERS response
    Steinigeweg, D. and Schütz, M. and Schlücker, S.
    Nanoscale 5 110-113 (2013)
    Dimers of metal nanospheres are well-known for their characteristic anisotropic optical response. Here, we demonstrate in single-particle SERS experiments that individual gold trimers and 3D superstructures exhibit a polarization-independent SERS response. This optical behavior of single particle clusters provides constant SERS signals, independent of the mutual orientation of the incident laser polarization and the plasmonic nanostructure, which is desired or even required in many SERS applications. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c2nr31982a
  • 2013 • 54 The anodic stripping voltammetry of nanoparticles: Electrochemical evidence for the surface agglomeration of silver nanoparticles
    Toh, H.S. and Batchelor-McAuley, C. and Tschulik, K. and Uhlemann, M. and Crossley, A. and Compton, R.G.
    Nanoscale 5 4884-4893 (2013)
    Analytical expressions for the anodic stripping voltammetry of metallic nanoparticles from an electrode are provided. First, for reversible electron transfer, two limits are studied: that of diffusionally independent nanoparticles and the regime where the diffusion layers originating from each particle overlap strongly. Second, an analytical expression for the voltammetric response under conditions of irreversible electron transfer kinetics is also derived. These equations demonstrate how the peak potential for the stripping process is expected to occur at values negative of the formal potential for the redox process in which the surface immobilised nanoparticles are oxidised to the corresponding metal cation in the solution phase. This work is further developed by considering the surface energies of the nanoparticles and its effect on the formal potential for the oxidation. The change in the formal potential is modelled in accordance with the equations provided by Plieth [J. Phys. Chem., 1982, 86, 3166-3170]. The new analytical expressions are used to investigate the stripping of silver nanoparticles from a glassy carbon electrode. The relative invariance of the stripping peak potential at low surface coverages of silver is shown to be directly related to the surface agglomeration of the nanoparticles. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3nr00898c
  • 2013 • 53 Electrochemical detection of chloride levels in sweat using silver nanoparticles: A basis for the preliminary screening for cystic fibrosis
    Toh, H.S. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    Analyst 138 4292-4297 (2013)
    Cystic fibrosis is a common disease which has an associated characteristic symptom of high sweat chloride content. Thus, chloride ion quantification in sweat is important towards the screening of cystic fibrosis. Electrochemical methods, being cost effective and convenient, can be exploited for this. The electrochemical oxidation of silver nanoparticles in the absence of chloride ions gives one voltammetric signal related to the oxidation of silver to silver ions. The presence of chloride ions in the solution causes the appearance of an additional signal at a lower potential which is related to the oxidation of silver to silver chloride. This signal has a peak height which correlates linearly with the concentration of chloride ions from 2 mM to 40 mM when the electrochemical experiments are performed on silver nanoparticle modified screen printed electrodes. Thus, reliable quantification was found to be achievable. Furthermore, chloride ion levels of diluted synthetic sweat samples are measured accurately with the modified electrodes. Thus, the detection of the chloride ion concentration with a silver nanoparticle modified electrode provides a proof-of-concept for a point-of-care system for preliminary screening of cystic fibrosis. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3an00843f
  • 2013 • 52 'Sticky electrodes' for the detection of silver nanoparticles
    Tschulik, K. and Palgrave, R.G. and Batchelor-Mcauley, C. and Compton, R.G.
    Nanotechnology 24 (2013)
    Detection and quantification of nanoparticles in environmental systems is a task that requires reliable and affordable analytical methods. Here an approach using a cysteine-modified 'sticky' glassy carbon electrode is presented. The electrode is immersed in a silver nanoparticle containing electrolyte and left in this suspension without an applied potential, i.e. under open circuit condition, for a variable amount of time. The amount of silver nanoparticles immobilized on the electrode within this sticking time is then determined by oxidative stripping, yielding the anodic charge and thus the amount of Ag nanoparticles sticking to the electrode surface. When using a cysteine-modified glassy carbon electrode, significant and reproducible amounts of silver nanoparticles stick to the surface, which is not the case for unmodified glassy carbon surfaces. Additionally, proof-of-concept experiments are performed on real seawater samples. These demonstrate that also under simulated environmental conditions an increased immobilization and hence improved detection of silver nanoparticles on cysteine-modified glassy carbon electrodes is achieved, while no inhibitive interference with this complex matrix is observed. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/24/29/295502
  • 2013 • 51 A kinetic study of oxygen reduction reaction and characterization on electrodeposited gold nanoparticles of diameter between 17 nm and 40 nm in 0.5 M sulfuric acid
    Wang, Y. and Laborda, E. and Ward, K.R. and Tschulik, K. and Compton, R.G.
    Nanoscale 5 9699-9708 (2013)
    Kinetic and mechanistic studies of the oxygen reduction reaction (ORR) in oxygen saturated 0.5 M sulfuric acid at 298 K at a gold macroelectrode and at an electrodeposited gold nanoparticle-modified glassy carbon electrode are reported. The conditions of electrodeposition are optimized to obtain small nanoparticles of diameter from 17 nm to 40 nm. The mechanism and kinetics of ORR on the gold macroelectrode are investigated and compared with those obtained for nanoparticle-modified electrodes. The mechanism for this system includes two electron and two proton transfers and hydrogen peroxide as the final product. The first electron transfer step corresponding to the reduction of O2 to O2 - is defined as the rate determining step. No significant changes are found for the nanoparticles here employed: electron transfer rate constant (k0) is k0,bulk = 0.30 cm s -1 on the bulk material and k0,nano = 0.21 cm s -1 on nanoparticles; transfer coefficient (α) changes from αbulk = 0.45 on macro-scale to αnano = 0.37 at the nano-scale. © The Royal Society of Chemistry 2013.
    view abstractdoi: 10.1039/c3nr02340k
  • 2013 • 50 Label-free SERS monitoring of chemical reactions catalyzed by small gold nanoparticles using 3D plasmonic superstructures
    Xie, W. and Walkenfort, B. and Schlücker, S.
    Journal of the American Chemical Society 135 1657-1660 (2013)
    Label-free in situ surface-enhanced Raman scattering (SERS) monitoring of reactions catalyzed by small gold nanoparticles using rationally designed plasmonic superstructures is presented. Catalytic and SERS activities are integrated into a single bifunctional 3D superstructure comprising small gold satellites self-assembled onto a large shell-isolated gold core, which eliminates photocatalytic side reactions. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/ja309074a
  • 2013 • 49 Medical applications of surface-enhanced Raman scattering
    Xie, W. and Schlücker, S.
    Physical Chemistry Chemical Physics 15 5329-5344 (2013)
    This perspective article provides an overview of selected medical applications of surface-enhanced Raman scattering (SERS), highlighting recent developments and trends. The use of SERS for detection, analysis and imaging has attracted great interest in the past decade owing to its high sensitivity and molecular fingerprint specificity. SERS can deliver chemical and structural information from analytes rapidly and nondestructively in a label-free manner. Alternatively, SERS labels or nanotags, when conjugated to target-specific ligands, can be employed for the selective detection and localization of the corresponding target molecule. Biomedical applications based on both approaches are highlighted. © 2013 the Owner Societies.
    view abstractdoi: 10.1039/c3cp43858a
  • 2012 • 48 Coarsening phenomena of metal nanoparticles and the influence of the support pre-treatment: Pt/TiO 2(110)
    Behafarid, F. and Roldan Cuenya, B.
    Surface Science 606 908-918 (2012)
    One of the technologically most important requirements for the application of oxide-supported metal nanoparticles (NPs) in the fields of molecular electronics, plasmonics, and catalysis is the achievement of thermally stable systems. For this purpose, a thorough understanding of the different pathways underlying thermally-driven coarsening phenomena, and the effect of the nanoparticle synthesis method, support morphology, and degree of support reduction on NP sintering is needed. In this study, the sintering of supported metal NPs has been monitored via scanning tunneling microscopy combined with simulations following the Ostwald ripening and diffusion-coalescence models. Modifications were introduced to the diffusion-coalescence model to incorporate the correct temperature dependence and energetics. Such methods were applied to describe coarsening phenomena of physical-vapor deposited (PVD) and micellar Pt NPs supported on TiO 2(110). The TiO 2(110) substrates were exposed to different pre-treatments, leading to reduced, oxidized and polymer-modified TiO 2 surfaces. Such pre-treatments were found to affect the coarsening behavior of the NPs. No coarsening was observed for the micellar Pt NPs, maintaining their as-prepared size of ~ 3 nm after annealing in UHV at 1060 °C. Regardless of the initial substrate pre-treatment, the average size of the PVD-grown NPs was found to increase after identical thermal cycles, namely, from 0.5 ± 0.2 nm to 1.0 ± 0.3 nm for pristine TiO 2, and from 0.8 ± 0.3 nm to 1.3 ± 0.6 nm for polymer-coated TiO 2 after identical thermal treatments. Although no direct real-time in situ microscopic evidence is available to determine the dominant coarsening mechanism of the PVD NPs unequivocally, our simulations following the diffusion-coalescence coarsening route were in significantly better agreement with the experimental data as compared to those based on the Ostwald-ripening model. The enhanced thermal stability of the micellar NPs as compared to the PVD clusters might be related to their initial larger NP size, narrower size distribution, and larger interparticle distances. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.susc.2012.01.022
  • 2012 • 47 Comparison of micro- and nanoscale Fe +3-containing (Hematite) particles for their toxicological properties in human lung cells in vitro
    Bhattacharya, K. and Hoffmann, E. and Schins, R.F.P. and Boertz, J. and Prantl, E.-M. and Alink, G.M. and Byrne, H.J. and Kuhlbusch, T.A.J. and Rahman, Q. and Wiggers, H. and Schulz, C. and Dopp, E.
    Toxicological Sciences 126 173-182 (2012)
    The specific properties of nanoscale particles, large surface-to-mass ratios and highly reactive surfaces, have increased their commercial application in many fields. However, the same properties are also important for the interaction and bioaccumulation of the nonbiodegradable nanoscale particles in a biological system and are a cause for concern. Hematite (α-Fe 2O 3), being a mineral form of Fe(III) oxide, is one of the most used iron oxides besides magnetite. The aim of our study was the characterization and comparison of biophysical reactivity and toxicological effects of α-Fe 2O 3 nano- (d < 100 nm) and microscale (d < 5 μm) particles in human lung cells. Our study demonstrates that the surface reactivity of nanoscale α-Fe 2O 3 differs from that of microscale particles with respect to the state of agglomeration, radical formation potential, and cellular toxicity. The presence of proteins in culture medium and agglomeration were found to affect the catalytic properties of the hematite nano- and microscale particles. Both the nano- and microscale α-Fe 2O 3 particles were actively taken up by human lung cells in vitro, although they were not found in the nuclei and mitochondria. Significant genotoxic effects were only found at very high particle concentrations (> 50 μg/ml). The nanoscale particles were slightly more potent in causing cyto- and genotoxicity as compared with their microscale counterparts. Both types of particles induced intracellular generation of reactive oxygen species. This study underlines that α-Fe 2O 3 nanoscale particles trigger different toxicological reaction pathways than microscale particles. However, the immediate environment of the particles (biomolecules, physiological properties of medium) modulates their toxicity on the basis of agglomeration rather than their actual size. © The Author 2012. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.
    view abstractdoi: 10.1093/toxsci/kfs014
  • 2012 • 46 Nanoscale size effect on surface spin canting in iron oxide nanoparticles synthesized by the microemulsion method
    Darbandi, M. and Stromberg, F. and Landers, J. and Reckers, N. and Sanyal, B. and Keune, W. and Wende, H.
    Journal of Physics D: Applied Physics 45 (2012)
    Uniformly sized and crystalline iron oxide nanoparticles (IONPs) with spinel structure and mean diameters of about 3, 6 and 9nm were synthesized in high yield using the microemulsion route at room temperature. The nanoparticles (NPs) were stabilized in situ by organic surfactant molecules which acted both as a stabilizer of the microemulsion system and as a capping layer of the NP surface. NP size control was attained by careful adjustment of the preparation conditions. The structure, morphology and NP size distribution were investigated by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. A particular effort was devoted in this work to study the effect of size and capping of these NPs on their magnetic structure by in-field Mössbauer spectroscopy at 4.2K. The mean canting angle (relative to the applied field direction) of the Fe spins was observed to increase with decreasing NP size due to the enhanced surface-to-volume ratio. Comparing bare and capped NPs of the same diameter, we verified that the spin canting was not affected by the organic capping. This implied almost identical magnetic orientations of bare and capped NPs. Simultaneously, the capping material was capable of preventing agglomeration effects which can occur in case of direct particle contact. Using a core/shell model, we showed that spin canting originated from the surface shell of the NPs. Furthermore, the Mössbauer spectral parameters provided evidence for the existence of a high fraction of Fe 3O 4 (magnetite) in the IONP. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0022-3727/45/19/195001
  • 2012 • 45 Understanding properties of electrified interfaces as a prerequisite for label-free DNA hybridization detection
    Gebala, M. and Schuhmann, W.
    Physical Chemistry Chemical Physics 14 14933-14942 (2012)
    Label-free electrochemical detection of DNA hybridization with high selectivity and sensitivity is only achievable if the properties of DNA at an electrified interface are understood in depth. After a short summary of concepts of electrochemical DNA detection as well as initial attempts towards label-free DNA assays the review discusses the physico-chemical properties and differences between single-stranded and double-stranded DNA immobilized at electrode surfaces in the light of their persistence lengths, structural conformation, impact of the charge screening by ion condensation and the electric field generated upon polarization of the electrode. Electrochemical impedance spectroscopy as a tool for label-free elucidation of DNA hybridization is reviewed and the necessity for an in-depth understanding of the interfacial properties is highlighted. Our major aim is to demonstrate the advantageous application of specifically designed intercalating compounds for the design of label-free detection of DNA hybridization. This journal is © 2012 the Owner Societies.
    view abstractdoi: 10.1039/c2cp42382k
  • 2012 • 44 Impact of the nanoparticle-protein corona on colloidal stability and protein structure
    Gebauer, J.S. and Malissek, M. and Simon, S. and Knauer, S.K. and Maskos, M. and Stauber, R.H. and Peukert, W. and Treuel, L.
    Langmuir 28 9673-9679 (2012)
    In biological fluids, proteins may associate with nanoparticles (NPs), leading to the formation of a so-called "protein corona" largely defining the biological identity of the particle. Here, we present a novel approach to assess apparent binding affinities for the adsorption/desorption of proteins to silver NPs based on the impact of the corona formation on the agglomeration kinetics of the colloid. Affinities derived from circular dichroism measurements complement these results, simultaneously elucidating structural changes in the adsorbed protein. Employing human serum albumin as a model, apparent affinities in the nanomolar regime resulted from both approaches. Collectively, our findings now allow discrimination between the formation of protein mono- and multilayers on NP surfaces. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/la301104a
  • 2012 • 43 Competition between ordering, twinning, and segregation in binary magnetic 3d-5d nanoparticles: A supercomputing perspective
    Gruner, M.E. and Entel, P.
    International Journal of Quantum Chemistry 112 277-288 (2012)
    The benefit of massively parallel supercomputers for technologically relevant applications in the field of materials science is demonstrated at the example of first-principles total energy calculations of magnetic binary transition metal nanoparticles containing up to 1415 3d and 5d transition metal atoms. The simulations, which take into account structural optimizations without symmetry constraints, reveal the size-dependent evolution of the energetic order of single crystalline and multiply twinned Fe-Pt nanoparticles up to 4 nm in diameter, which are discussed as promising building blocks for future ultra-high density data recording media. Although at small diameters, multiply twinned morphologies are preferred, we can show that an energetic crossover to a single crystalline, ordered arrangement can be expected at diameters around four nanometers. The comparison with Co-Pt indicates that the contributions of the interfaces in multiply twinned structures are of similar importance as the surface and cannot be neglected especially for small particle sizes. The results imply that for Co-Pt particles segregation of Pt to the surface and the formation of a Pt-depleted subsurface layer is also dominant for nanometer-sized single crystalline particles and may help to stabilize particles with partial L10 order, whereas for Fe-Pt multiple twinning is the most important equilibrium mechanism for small particle sizes. Hybrid combinations of the most favorable ordering motifs, that is, L10-type ordering in the particle core in combination with segregation in the outer shells, may thus lead to highly stable morphologies, which could dominate the growth process. © 2011 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/qua.23254
  • 2012 • 42 Detection of DNA hybridization using electrochemical impedance spectroscopy and surface enhanced Raman scattering
    Grützke, S. and Abdali, S. and Schuhmann, W. and Gebala, M.
    Electrochemistry Communications 19 59-62 (2012)
    The formation of double-stranded DNA (dsDNA) at gold electrodes decorated with a monolayer of gold nanoparticles bound through a self-assembled dithiol monolayer is detected via specific intercalation of proflavine. Hybridization as well as sequential built-up of the electrode architecture is monitored using Faradaic electrochemical impedance spectroscopy (EIS) as well as surface enhanced Raman scattering (SERS). The adsorption of secondary gold nanoparticles allow for amplified detection of the dsDNA integrated intercalator in a vertical gap mode configuration. The experimental design thus allows probing presence of the intercalator inside the dsDNA. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elecom.2012.03.026
  • 2012 • 41 Au, @ZrO 2 yolk-shell catalysts for CO oxidation: Study of particle size effect by ex-post size control of Au cores
    Güttel, R. and Paul, M. and Galeano, C. and Schüth, F.
    Journal of Catalysis 289 100-104 (2012)
    Gold nanoparticles supported on transition metal oxides are found to exhibit a pronounced particle size effect in CO oxidation. However, the preparation of comparable supported gold nanoparticles with different sizes remains challenging, since the catalytic behavior of these materials is very sensitive to the preparation conditions. To overcome this difficulty, Au, @ZrO 2 catalysts with gold core sizes between 5 and 15 nm were prepared by partial leaching of gold in an ex-post manner. The material obtained offers a unique comparability for particle size effect studies in CO oxidation. No effect of gold particle size was observed in the studied size range. © 2012 Elsevier Inc. All rights reserved.
    view abstractdoi: 10.1016/j.jcat.2012.01.021
  • 2012 • 40 Cytotoxicity and ion release of alloy nanoparticles
    Hahn, A. and Fuhlrott, J. and Loos, A. and Barcikowski, S.
    Journal of Nanoparticle Research 14 (2012)
    It is well-known that nanoparticles could cause toxic effects in cells. Alloy nanoparticles with yet unknown health risk may be released from cardiovascular implants made of Nickel-Titanium or Cobalt-Chromium due to abrasion or production failure. We show the bio-response of human primary endothelial and smooth muscle cells exposed to different concentrations of metal and alloy nanoparticles. Nanoparticles having primary particle sizes in the range of 5-250 nm were generated using laser ablation in three different solutions avoiding artificial chemical additives, and giving access to formulations containing nanoparticles only stabilized by biological ligands. Endothelial cells are found to be more sensitive to nanoparticle exposure than smooth muscle cells. Cobalt and Nickel nanoparticles caused the highest cytotoxicity. In contrast, Titanium, Nickel- Iron, and Nickel-Titanium nanoparticles had almost no influence on cells below a nanoparticle concentration of 10 lM. Nanoparticles in cysteine dissolved almost completely, whereas less ions are released when nanoparticles were stabilized in water or citrate solution. Nanoparticles stabilized by cysteine caused less inhibitory effects on cells suggesting cysteine to form metal complexes with bioactive ions in media. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-011-0686-3
  • 2012 • 39 Catalytic role of gold nanoparticle in GaAs nanowire growth: A density functional theory study
    Kratzer, P. and Sakong, S. and Pankoke, V.
    Nano Letters 12 943-948 (2012)
    The energetics of Ga, As, and GaAs species on the Au(111) surface (employed as a model for Au nanoparticles) is investigated by means of density functional calculations. Apart from formation of the compound Au 7Ga 2, Ga is found to form a surface alloy with gold with comparable ΔH ∼ -0.5 eV for both processes. Dissociative adsorption of As 2 is found to be exothermic by more than 2 eV on both clean Au(111) and AuGa surface alloys. The As-Ga species formed by reaction of As with the surface alloy is sufficiently stable to cover the surface of an Au particle in vacuo in contact with a GaAs substrate. The results of the calculations are interpreted in the context of Au-catalyzed growth of GaAs nanowires. We argue that arsenic is supplied to the growth zone of the nanowire mainly by impingement of molecules on the gold particle and identify a regime of temperatures and As 2 partial pressures suitable for Au-catalyzed nanowire growth in molecular beam epitaxy. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/nl204004p
  • 2012 • 38 Upregulation of metallothioneins after exposure of cultured primary astrocytes to silver nanoparticles
    Luther, E.M. and Schmidt, M.M. and Diendorf, J. and Epple, M. and Dringen, R.
    Neurochemical Research 37 1639-1648 (2012)
    To test for the prolonged consequences of a short transient exposure of astrocytes to silver nanoparticles (AgNP), cultured primary astrocytes were incubated for 4 h in the presence of AgNP and the cell viability as well as various metabolic parameters were investigated during a subsequent incubation in AgNP-free medium. Acute exposure of astrocytes to AgNP led to a concentration-dependent increase in the specific cellular silver content to up to 46 nmol/mg protein, but did not compromise cell viability. During a subsequent incubation of the cells in AgNP-free medium, the cellular silver content of AgNPtreated astrocytes remained almost constant for up to 7 days. The cellular presence of AgNP did neither induce any delayed cell toxicity nor were alterations in cellular glucose consumption, lactate production or in the cellular ratio of glutathione to glutathione disulfide observed. However, Western blot analysis and immunocytochemical staining revealed that AgNP-treated astrocytes strongly upregulated the expression of metallothioneins. These results demonstrate that a prolonged presence of accumulated AgNP does not compromise the viability and the basal metabolism of cultured astrocytes and suggest that the upregulation of metallothioneins may help to prevent silver-mediated toxicity that could be induced by AgNPderived silver ions. © Springer Science+Business Media, LLC 2012.
    view abstractdoi: 10.1007/s11064-012-0767-4
  • 2012 • 37 Silver, gold, and alloyed silver-gold nanoparticles: Characterization and comparative cell-biologic action
    Mahl, D. and Diendorf, J. and Ristig, S. and Greulich, C. and Li, Z.A. and Farle, M. and Köller, M. and Epple, M.
    Journal of Nanoparticle Research 14 (2012)
    Silver, gold, and silver-gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy waterbased synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly(N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15-25 nm), gold (5-6 nm), and silver-gold (50:50; 10-12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver-gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver-gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver-gold nanoparticles in the concentration range of 5-20 μg mL -1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-012-1153-5
  • 2012 • 36 Enhanced electrocatalytic stability of platinum nanoparticles supported on a nitrogen-doped composite of carbon nanotubes and mesoporous titania under oxygen reduction conditions
    Masa, J. and Bordoloi, A. and Muhler, M. and Schuhmann, W. and Xia, W.
    ChemSusChem 5 523-525 (2012)
    Cheers for titania: An N-doped composite of carbon nanotubes (CNTs) and mesoporous TiO 2 is used as support for Pt nanoparticles applied in the oxygen reduction reaction. The composite Pt/N-TiO 2-CNT shows a higher stability than Pt particles on carbon black or N-doped CNTs, as indicated by accelerated stress tests of up to 2000 cycles. The enhanced stability is attributed to strong interactions between TiO 2 and Pt and a higher corrosion resistance of TiO 2 as well as CNTs. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cssc.201100643
  • 2012 • 35 Interface of nanoparticle-coated electropolished stents
    Neumeister, A. and Bartke, D. and Bärsch, N. and Weingärtner, T. and Guetaz, L. and Montani, A. and Compagnini, G. and Barcikowski, S.
    Langmuir 28 12060-12066 (2012)
    Nanostructures entail a high potential for improving implant surfaces, for instance, in stent applications. The electrophoretic deposition of laser-generated colloidal nanoparticles is an appropriate tool for creating large-area nanostructures on surfaces. Until now, the bonding and characteristics of the interface between deposited nanoparticles and the substrate surface has not been known. It is investigated using X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron microscopy to characterize an electropolished NiTi stent surface coated by laser-generated Au and Ti nanoparticles. The deposition of elemental Au and Ti nanoparticles is observed on the total 3D surface. Ti-coated samples are composed of Ti oxide and Ti carbide because of nanoparticle fabrication and the coating process carried out in 2-propanol. The interface between nanoparticles and the electropolished surface consists of a smooth, monotone elemental depth profile. The interface depth is higher for the Ti nanoparticle coating than for the Au nanoparticle coating. This smooth depth gradient of Ti across the coating-substrate intersection and the thicker interface layer indicate the hard bonding of Ti-based nanoparticles on the surface. Accordingly, electron microscopy reveals nanoparticles adsorbed on the surface without any sorption-blocking intermediate layer. The physicomechanical stability of the bond may benefit from such smooth depth gradients and direct, ligand-free contact. This would potentially increase the coating stability during stent application. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/la300308w
  • 2012 • 34 Copper nanoparticles stabilized on nitrogen-doped carbon nanotubes as efficient and recyclable catalysts for alkyne/aldehyde/cyclic amine A 3-type coupling reactions
    Ramu, V.G. and Bordoloi, A. and Nagaiah, T.C. and Schuhmann, W. and Muhler, M. and Cabrele, C.
    Applied Catalysis A: General 431-432 88-94 (2012)
    Metallic copper nanoparticles have been efficiently dispersed and stabilized on nitrogen-doped carbon nanotubes. They are about 8-10 nm in diameter and highly resistant against bulk oxidation. Their catalytic activity and recyclability have been investigated in A 3-type coupling reactions for the synthesis of propargylamines. It was easily possible to prepare diastereomerically pure derivatives of proline and to efficiently recover and reuse the supported catalyst several times. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apcata.2012.04.019
  • 2012 • 33 Surfactant-induced nonhydrolytic synthesis of phase-pure ZrO2 nanoparticles from metal-organic and oxocluster precursors
    Sliem, M.A. and Schmidt, D.A. and Bétard, A. and Kalidindi, S.B. and Gross, S. and Havenith, M. and Devi, A. and Fischer, R.A.
    Chemistry of Materials 24 4274-4282 (2012)
    Nonhydrolytic/non-sol-gel pyrolytic synthesis technique, as a convenient method, was applied to synthesize zirconium oxide nanoparticles (ZrO2 NPs). Pyrolysis of either the mononuclear keto ester/alkoxide complex zirconium bis(isopropoxide)bis(tert-butylacetoacetate) [Zr(OiPr) 2(tbaoac)2] (I) or the oligonuclear oxocluster compound [Zr6(OH)4O4(OMc)12] (II, Mc = methacrylate) generated ZrO2 NPs at moderate conditions of 300-400 °C. Trioctylamine, stearic acid, and/or oleic acid, which act as both solvents and stabilizing agents, were used. Under the adopted process conditions, the stabilizing agent oleic acid plays a vital role in determining the phase of as-synthesized colloidal ZrO2 nanoparticles, which yield the high-temperature tetragonal phase at moderate conditions of 335 °C. Those as-synthesized samples that contained both monoclinic and tetragonal ZrO2 phases (depending on the choice of the surfactant) were transformed into pure tetragonal phase at 1000 °C. An unambiguous phase determination of ZrO2 nanoparticles was carried out by the combination of powder X-ray diffraction (XRD) and Raman spectroscopy. Furthermore, the samples were analyzed by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared (FT-IR) spectroscopy to elucidate the structure, chemical composition, and morphology of the obtained nanoparticles. Also, the phase transformations of the as-synthesized ZrO2 nanoparticles upon annealing were followed via Raman spectroscopy. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/cm301128a
  • 2012 • 32 Impact of metal nanoparticles on germ cell viability and functionality
    Taylor, U. and Barchanski, A. and Kues, W. and Barcikowski, S. and Rath, D.
    Reproduction in Domestic Animals 47 359-368 (2012)
    Metal nanoparticles play an increasing role in consumer products, biomedical applications and in the work environment. Therefore, the effects of nanomaterials need to be properly understood. This applies especially to their potential reproductive toxicology (nanoreprotoxicity), because any shortcomings in this regard would be reflected into the next generation. This review is an attempt to summarize the current knowledge regarding the effects of nanoparticles on reproductive outcomes. A comprehensive collection of significant experimental nanoreprotoxicity data is presented, which highlight how the toxic effect of nanoparticles can be influenced, not only by the particles' chemical composition, but also by particle size, surface modification, charge and to a considerable extent on the experimental set-up. The period around conception is characterized by considerable cytological and molecular restructuring and is therefore particularly sensitive to disturbances. Nanoparticles are able to penetrate through biological barriers into reproductive tissue and at least can have an impact on sperm vitality and function as well as embryo development. Particularly, further investigations are urgently needed on the repetitively shown effect of the ubiquitously used titanium dioxide nanoparticles on the development of the nervous system. It is recommended that future research focuses more on the exact mechanism behind the observed effects, because such information would facilitate the production of nanoparticles with increased biocompatibility. © 2012 Blackwell Verlag GmbH.
    view abstractdoi: 10.1111/j.1439-0531.2012.02099.x
  • 2012 • 31 Toxicity of gold nanoparticles on somatic and reproductive cells
    Taylor, U. and Barchanski, A. and Garrels, W. and Klein, S. and Kues, W. and Barcikowski, S. and Rath, D.
    Advances in Experimental Medicine and Biology 733 125-133 (2012)
    Along with the number of potential applications for gold nanoparticles (AuNP) especially for medical and scientific purposes, the interest in possible toxic effects of such particles is rising. The general perception views nanosized gold colloids as relatively inert towards biological systems. However, a closer analysis of pertinent studies reveals a more complex picture. While the chemical compound of which the nanoparticles consists plays an important role, further biocompatibility determining aspects have been made out. The vast majority of trials concerning AuNP-toxicity were performed using somatic cell culture lines. The results show a considerable dependency of toxic effects on size, zeta potential and surface functionalisation. In vivo studies on this subject are still rare. Based on the existing data it can be assumed, that a dosage of under <400 μg Au/kg showed no untoward effects. If higher amounts were applied toxicity depended on route of administration and particle size. Since nanoparticles have been shown to cross reproduction-relevant biological barriers such as the blood-testicle and the placental barrier the question of their reprotoxicity arises. Yet data concerning this subject is far from adequate. Regarding gametes, recent experiments showed a dose-dependent sensitivity of spermatozoa towards AuNP. Oocytes have not yet been tested in that respect. Interestingly, so far no effects were detected on embryos after gold nanoparticle exposure. In conclusion, the biocompatibility of gold nanoparticles depends on a range of particle specific aspects as well as the choice of target tissue. Further clarification of such matters are subject to ongoing research. © 2012 Springer Science+Business Media B.V.
    view abstractdoi: 10.1007/978-94-007-2555-3_12
  • 2012 • 30 Quantifying the influence of polymer coatings on the serum albumin corona formation around silver and gold nanoparticles
    Treuel, L. and Malissek, M. and Grass, S. and Diendorf, J. and Mahl, D. and Meyer-Zaika, W. and Epple, M.
    Journal of Nanoparticle Research 14 (2012)
    When nanoparticles (NPs) come into contact with biological fluids, proteins, and other biomolecules interact with their surface. Upon exposure to biological fluids a layer of proteins adsorbs onto their surface, the so-called protein corona, and interactions of biological systems with NPs are therefore mediated by this corona. Here, interactions of serum albumin with silver and gold NPs were quantitatively investigated using circular dichroism spectroscopy. Moreover, surface enhanced Raman spectroscopy was used for further elucidation of protein binding to silver surfaces. The decisive role of poly(vinylpyrrolidone), coatings on the protein adsorption was quantitatively described for the first time and the influential role of the polymer coatings is discussed. Research in nanotoxicology may benefit from such molecular scale data as well as scientific approaches seeking to improve nanomedical applications by using a wide range of polymer surface coatings to optimize biological transport and medical action of NPs. © Springer Science+Business Media B.V. 2012.
    view abstractdoi: 10.1007/s11051-012-1102-3
  • 2012 • 29 How citrate ligands affect nanoparticle adsorption to microparticle supports
    Wagener, P. and Schwenke, A. and Barcikowski, S.
    Langmuir 28 6132-6140 (2012)
    Residual ligands from colloidal synthesis of nanoparticles influence adsorption of nanoparticles to supports and may complicate fabrication of nanoparticle-decorated microparticles. In this work, we studied the adsorption of completely ligand-free metal nanoparticles and controlled ligand-functionalized nanoparticles to chemically inert microparticle supports. Adsorption of ligand-free silver nanoparticles to barium sulfate microparticle supports is a quantitative, nonreversible process following Freundlich adsorption isotherm. However, adsorption efficiency is very sensitive to ligand concentration applied during laser-based synthesis of silver nanoparticles: exceeding a specific threshold concentration of 50 μmol/L citrate equal to a nanoparticle ligand surface coverage of about 50%, results in an almost complete prevention of nanoparticle adsorption because of electrosteric repulsion by ligand shell. Laser-based synthesis of nanoparticle-decorated microparticles is demonstrated with a variety of metal nanoparticles (Ag, Au, Pt, Fe) and supporting microparticles (calcium phosphate, titanium dioxide, barium sulfate) with application potential in heterogeneous catalysis or biomedicine where ligand control offers extra value, like enhanced catalytic activity or biocompatibility. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/la204839m
  • 2011 • 28 A guideline for atomistic design and understanding of ultrahard nanomagnets
    Antoniak, C. and Gruner, M.E. and Spasova, M. and Trunova, A.V. and Römer, F.M. and Warland, A. and Krumme, B. and Fauth, K. and Sun, S. and Entel, P. and Farle, M. and Wende, H.
    Nature Communications 2 (2011)
    Magnetic nanoparticles are of immense current interest because of their possible use in biomedical and technological applications. Here we demonstrate that the large magnetic anisotropy of FePt nanoparticles can be significantly modified by surface design. We employ X-ray absorption spectroscopy offering an element-specific approach to magnetocrystalline anisotropy and the orbital magnetism. Experimental results on oxide-free FePt nanoparticles embedded in Al are compared with large-scale density functional theory calculations of the geometric- and spin-resolved electronic structure, which only recently have become possible on world-leading supercomputer architectures. The combination of both approaches yields a more detailed understanding that may open new ways for a microscopic design of magnetic nanoparticles and allows us to present three rules to achieve desired magnetic properties. In addition, concrete suggestions of capping materials for FePt nanoparticles are given for tailoring both magnetocrystalline anisotropy and magnetic moments. © 2011 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms1538
  • 2011 • 27 Golden Perspective: Application of Laser-Generated Gold Nanoparticle Conjugates in Reproductive Biology
    Barchanski, A. and Taylor, U. and Klein, S. and Petersen, S. and Rath, D. and Barcikowski, S.
    Reproduction in Domestic Animals 46 42-52 (2011)
    Contents: The current demand for female calves has grown rapidly and controlling the sex of offspring provides an economically flexible management for the livestock producer. The only functioning method of efficiently producing separate populations of X and Y sperm in mammals is based on relative DNA differentiation by high-speed flow cytometry. In this context, gold nanoparticles conjugated to sex chromosome-specific moieties display promising application as novel fluorophor-alternative for the high-throughput screening, since they feature no photo bleaching, high quantum yield, good biocompatibility and the possibility of non-destructive membrane penetration. Especially, gold nanoparticles fabricated by pulsed laser ablation are in the recent focus of interest, due to excellent biocompatibility, fabrication-dependent, tuneable particle size as well as surface charge and ease of (bio)-functionalization with a remarkably strong ligand binding. For the purpose of our studies functionalized gold nanoparticles may be used as novel markers for sex-sorting of mammalian sperm and, depending on the selected probe, also for the selection of sperm with heritable DNA-sequences interesting for animal breeding. © 2011 Blackwell Verlag GmbH.
    view abstractdoi: 10.1111/j.1439-0531.2011.01844.x
  • 2011 • 26 Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions
    Becker, M.J. and Xia, W. and Tessonnier, J.-P. and Blume, R. and Yao, L. and Schlögl, R. and Muhler, M.
    Carbon 49 5253-5264 (2011)
    An industrially applicable cobalt-based catalyst was optimized for the production of multiwalled carbon nanotubes (CNTs) from ethene in a hot-wall reactor. A series of highly active Co-Mn-Al-Mg spinel-type oxides with systematically varied Co: Mn ratios was synthesized by precipitation and calcined at different temperatures. The addition of Mn drastically enhanced the catalytic activity of the Co nanoparticles resulting in an extraordinarily high CNTyield of up to 249 g CNT/gcat. All quaternary catalysts possessed an excellent selectivity towards the growth of CNTs. The detailed characterization of the obtained CNTs by electron microscopy, Raman spectroscopy and thermogravimetry demonstrated that a higher Mn content results in a narrower CNT diameter distribution, while the morphology of the CNTs and their oxidation resistance remains rather similar. The temperature- programmed reduction of the calcined precursors as well as in situ X-ray absorption spectroscopy investigations during the growth revealed that the remarkable promoting effect of the Mn is due to the presence of monovalent Mn (II) oxide in the working catalyst, which enhances the catalytic activity of the metallic Co nanoparticles by strong metal-oxide interactions. The observed correlations between the added Mn promoter and the catalytic performance are of high relevance for the production of CNTs on an industrial scale. © 2011 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.carbon.2011.07.043
  • 2011 • 25 Photomodulation of the magnetisation of Co nanocrystals decorated with Rhodamine B
    Comesaña-Hermo, M. and Estivill, R. and Ciuculescu, D. and Amiens, C. and Farle, M. and Batat, P. and Jonusauskas, G. and McClenaghan, N.D. and Lecante, P. and Tardin, C. and Mazeres, S.
    ChemPhysChem 12 2915-2919 (2011)
    How exciting! Upon excitation of Rhodamine B with visible light in magnetic Co nanocrystal-Rhodamine B nanocomposites, electron transfer from the nanocrystal to the dye is evidenced as well as an increase in magnetisation (see picture), affording a new access to photomodulation of the magnetic properties of nanocrystal assemblies. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.201100616
  • 2011 • 24 Comparison of nanoparticle-mediated transfection methods for DNA expression plasmids: Efficiency and cytotoxicity
    Durán, M.C. and Willenbrock, S. and Barchanski, A. and Müller, J.-M.V. and Maiolini, A. and Soller, J.T. and Barcikowski, S. and Nolte, I. and Feige, K. and Murua Escobar, H.
    Journal of Nanobiotechnology 9 (2011)
    Background: Reproducibly high transfection rates with low methodology-induced cytotoxic side effects are essential to attain the required effect on targeted cells when exogenous DNA is transfected. Different approaches and modifications such as the use of nanoparticles (NPs) are being evaluated to increase transfection efficiencies. Several studies have focused on the attained transfection efficiency after NP-mediated approaches. However, data comparing toxicity of these novel approaches with conventional methods is still rare.Transfection efficiency and methodology-induced cytotoxicity were analysed after transfection with different NP-mediated and conventional approaches. Two eukaryotic DNA-expression-plasmids were used to transfect the mammalian cell line MTH53A applying six different transfection protocols: conventional transfection reagent (FuGENE HD, FHD), FHD in combination with two different sizes of stabilizer-free laser-generated AuNPs (PLAL-AuNPs_S1,_S2), FHD and commercially available AuNPs (Plano-AuNP), and two magnetic transfection protocols. 24 h post transfection efficiency of each protocol was analysed using fluorescence microscopy and GFP-based flow cytometry. Toxicity was assessed measuring cell proliferation and percentage of propidium iodide (PI%) positive cells. Expression of the respective recombinant proteins was evaluated by immunofluorescence.Results: The addition of AuNPs to the transfection protocols significantly increased transfection efficiency in the pIRES-hrGFPII-eIL-12 transfections (FHD: 16%; AuNPs mean: 28%), whereas the magnet-assisted protocols did not increase efficiency. Ligand-free PLAL-AuNPs had no significant cytotoxic effect, while the ligand-stabilized Plano-AuNPs induced a significant increase in the PI% and lower cell proliferation. For pIRES-hrGFPII-rHMGB1 transfections significantly higher transfection efficiency was observed with PLAL-AuNPs (FHD: 31%; PLAL-AuNPs_S1: 46%; PLAL-AuNPs_S2: 50%), while the magnet-assisted transfection led to significantly lower efficiencies than the FHD protocol. With PLAL-AuNPs_S1 and _S2 the PI% was significantly higher, yet no consistent effect of these NPs on cell proliferation was observed. The magnet-assisted protocols were least effective, but did result in the lowest cytotoxic effect.Conclusions: This study demonstrated that transfection efficiency of DNA-expression-plasmids was significantly improved by the addition of AuNPs. In some combinations the respective cytotoxicity was increased depending on the type of the applied AuNPs and the transfected DNA construct. Consequently, our results indicate that for routine use of these AuNPs the specific nanoparticle formulation and DNA construct combination has to be considered. © 2011 Durán et al; licensee BioMed Central Ltd.
    view abstractdoi: 10.1186/1477-3155-9-47
  • 2011 • 23 Plasmonically active micron-sized beads for integrated solid-phase synthesis and label-free SERS analysis
    Gellner, M. and Niebling, S. and Kuchelmeister, H.Y. and Schmuck, C. and Schlücker, S.
    Chemical Communications 47 12762-12764 (2011)
    Self-assembly of gold nanospheres with a very thin glass shell onto the surface of beads yields a plasmonically active micron-sized substrate for integrated solid-phase synthesis and label-free SERS analysis. The proof-of-principle of this approach is demonstrated by the vibrational spectroscopic discrimination of three distinct amino acids and a dipeptide. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c1cc13562g
  • 2011 • 22 Cell type-specific responses of peripheral blood mononuclear cells to silver nanoparticles
    Greulich, C. and Diendorf, J. and Geßmann, J. and Simon, T. and Habijan, T. and Eggeler, G. and Schildhauer, T.A. and Epple, M. and Köller, M.
    Acta Biomaterialia 7 3505-3514 (2011)
    Silver nanoparticles (Ag-NP) are increasingly used in biomedical applications because of their remarkable antimicrobial activity. In biomedicine, Ag-NP are coated onto or embedded in wound dressings, surgical instruments and bone substitute biomaterials, such as silver-containing calcium phosphate cements. Free Ag-NP and silver ions are released from these coatings or after the degradation of a biomaterial, and may come into close contact with blood cells. Despite the widespread use of Ag-NP as an antimicrobial agent, there is a serious lack of information on the biological effects of Ag-NP on human blood cells. In this study, the uptake of Ag-NP by peripheral monocytes and lymphocytes (T-cells) was analyzed, and the influence of nanosilver on cell biological functions (proliferation, the expression of adhesion molecules, cytokine release and the generation of reactive oxygen species) was studied. After cell culture in the presence of monodispersed Ag-NP (5-30 μg ml -1 silver concentration), agglomerates of nanoparticles were detected within monocytes (CD14+) but not in T-cells (CD3+) by light microscopy, flow cytometry and combined focused ion beam/scanning electron microscopy. The uptake rate of nanoparticles was concentration dependent, and the silver agglomerates were typically found in the cytoplasm. Furthermore, a concentration-dependent activation (e.g. an increased expression of adhesion molecule CD54) of monocytes at Ag-NP concentrations of 10-15 μg ml -1 was observed, and cytotoxicity of Ag-NP-treated monocytes was observed at Ag-NP levels of 25 μg ml -1 and higher. However, no modulation of T-cell proliferation was observed in the presence of Ag-NP. Taken together, our results provide the first evidence for a cell-type-specific uptake of Ag-NP by peripheral blood mononuclear cells (PBMC) and the resultant cellular responses after exposure. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actbio.2011.05.030
  • 2011 • 21 Uptake and intracellular distribution of silver nanoparticles in human mesenchymal stem cells
    Greulich, C. and Diendorf, J. and Simon, T. and Eggeler, G. and Epple, M. and Köller, M.
    Acta Biomaterialia 7 347-354 (2011)
    Silver nanoparticles (Ag-NP) are widely used due to their well-known antibacterial effects. In medicine Ag-NP have found applications as wound dressings, surgical instruments and bone substitute biomaterials, e.g. silver-containing calcium phosphate cements. Depending on the coating technique, during resorption of a biomaterial Ag-NP may come into close contact with body tissues, including human mesenchymal stem cells (hMSC). Despite the widespread uses of Ag-NP, there is a serious lack of information concerning their biological effects on human cells. In this study the uptake of Ag-NP into hMSC has been analyzed and the intracellular distribution of Ag-NP after exposure determined. Non-agglomerated (dispersed) Ag-NP from the cell culture medium were detected as agglomerates of nanoparticles within the hMSC by combined focused ion beam/scanning electron microscopy. The silver agglomerates were typically located in the perinuclear region, as determined by light microscopy. Specific staining of cellular structures (endo-lysosomes, nuclei, Golgi complex and endoplasmatic reticulum) using fluorescent probes showed that the silver nanoparticles occurred mainly within endo-lysosomal structures, not in the cell nucleus, endoplasmic reticulum or Golgi complex. Quantitative determination of the uptake of Ag-NP by flow cytometry (scattergram analysis) revealed a concentration-dependent uptake of the particles which was significantly inhibited by chlorpromazine and wortmannin but not by nystatin, indicating clathrin-dependent endocytosis and macropinocytosis as the primary uptake mechanisms. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actbio.2010.08.003
  • 2011 • 20 Electrochemistry-controlled metal ion release from silicone elastomer nanocomposites through combination of different metal nanoparticles
    Hahn, A. and Günther, S. and Wagener, P. and Barcikowski, S.
    Journal of Materials Chemistry 21 10287-10289 (2011)
    Electrochemistry-controlled metal ion release is achieved using nanoparticle mixtures embedded into a silicone matrix. Synergistic metal ion release from silicone matrix filled with silver and copper nanoparticles as well as silver and gold nanoparticles embedded into silicone is investigated in terms of qualitative and quantitative influences. Results are compared to nanoparticle composites with only one metal. The mechanism enhancing the release of the less noble metal nanoparticle is based on the ion-mediated electrochemistry rather than on contact corrosion of both elements. A retardation as well as an enhancement of metal ion release is observed allowing a time- and rate-controlled design of bioactive nanocomposites. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0jm04480f
  • 2011 • 19 Stoichiometry of alloy nanoparticles from laser ablation of PtIr in acetone and their electrophoretic deposition on PtIr electrodes
    Jakobi, J. and Menéndez-Manjón, A. and Chakravadhanula, V.S.K. and Kienle, L. and Wagener, P. and Barcikowski, S.
    Nanotechnology 22 (2011)
    Charged Pt-Ir alloy nanoparticles are generated through femtosecond laser ablation of a Pt9Ir target in acetone without using chemical precursors or stabilizing agents. Preservation of the target's stoichiometry in the colloidal nanoparticles is confirmed by transmission electron microscopy (TEM)-energy-dispersive x-ray spectroscopy (EDX), high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM)-EDX elemental maps, high resolution TEM and selected area electron diffraction (SAED) measurements. Results are discussed with reference to thermophysical properties and the phase diagram. The nanoparticles show a lognormal size distribution with a mean Feret particle size of 26nm. The zeta potential of - 45mV indicates high stability of the colloid with a hydrodynamic diameter of 63nm. The charge of the particles enables electrophoretic deposition of nanoparticles, creating nanoscale roughness on three-dimensional PtIr neural electrodes within a minute. In contrast to coating with Pt or Ir oxides, this method allows modification of the surface roughness without changing the chemical composition of PtIr. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/22/14/145601
  • 2011 • 18 Colloidal metal nanoparticles as a component of designed catalyst
    Jia, C.-J. and Schüth, F.
    Physical Chemistry Chemical Physics 13 2457-2487 (2011)
    Recent advances in the synthesis of collidal metal nanoparticles of controlled sizes and shapes that are relevant for catalyst design are reviewed. Three main methods, based on colloid chemistry techniques in solution, i.e., chemical reduction of metal salt precursors, electrochemical synthesis, and controlled decomposition of organometallic compounds and metal-surfactant complexes, are used to synthesize metal nanoparticles. Their catalytic activity and selectivity depend on the shape, size and composition of the metal nanoparticles, and the support effect, as shown for many reactions in quasi-homogeneous and heterogeneous catalysis. A specially designed type of thermally stable catalysts - "embedded" metal catalysts, in which metal nanoparticles are isolated by porous support shells so that metal sintering is effectively avoided at high temperatures, are also introduced. The ultilization of pre-prepared colloidal metal nanoparticles with tuned size, shape and composition as components of designed catalysts opens up new field in catalysis. © 2011 the Owner Societies.
    view abstractdoi: 10.1039/c0cp02680h
  • 2011 • 17 Accumulation of silver nanoparticles by cultured primary brain astrocytes
    Luther, E.M. and Koehler, Y. and Diendorf, J. and Epple, M. and Dringen, R.
    Nanotechnology 22 (2011)
    Silver nanoparticles (AgNP) are components of various food industry products and are frequently used for medical equipment and materials. Although such particles enter the vertebrate brain, little is known on their biocompatibility for brain cells. To study the consequences of an AgNP exposure of brain cells we have treated astrocyte-rich primary cultures with polyvinylpyrrolidone (PVP)-coated AgNP. The incubation of cultured astrocytes with micromolar concentrations of AgNP for up to 24h resulted in a time-and concentration-dependent accumulation of silver, but did not compromise the cell viability nor lower the cellular glutathione content. In contrast, the incubation of astrocytes for 4h with identical amounts of silver as AgNO 3 already severely compromised the cell viability and completely deprived the cells of glutathione. The accumulation of AgNP by astrocytes was proportional to the concentration of AgNP applied and significantly lowered by about 30% in the presence of the endocytosis inhibitors chloroquine or amiloride. Incubation at 4 °C reduced the accumulation of AgNP by 80% compared to the values obtained for cells that had been exposed to AgNP at 37 °C. These data demonstrate that viable cultured brain astrocytes efficiently accumulate PVP-coated AgNP in a temperature-dependent process that most likely involves endocytotic pathways. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/22/37/375101
  • 2011 • 16 Modeling plasmonic scattering combined with thin-film optics
    Schmid, M. and Klenk, R. and Lux-Steiner, M.Ch. and Topič, M. and Krč, J.
    Nanotechnology 22 (2011)
    Plasmonic scattering from metal nanostructures presents a promising concept for improving the conversion efficiency of solar cells. The determination of optimal nanostructures and their position within the solar cell is crucial to boost the efficiency. Therefore we established a one-dimensional optical model combining plasmonic scattering and thin-film optics to simulate optical properties of thin-film solar cells including metal nanoparticles. Scattering models based on dipole oscillations and Mie theory are presented and their integration in thin-film semi-coherent optical descriptions is explained. A plasmonic layer is introduced in the thin-film structure to simulate scattering properties as well as parasitic absorption in the metal nanoparticles. A proof of modeling concept is given for the case of metal-island grown silver nanoparticles on glass and ZnO:Al/glass substrates. Using simulations a promising application of the nanoparticle integration is shown for the case of CuGaSe2 solar cells. © 2011 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/22/2/025204
  • 2011 • 15 Immuno-surface-enhanced coherent anti-Stokes Raman scattering microscopy: Immunohistochemistry with target-specific metallic nanoprobes and nonlinear Raman microscopy
    Schlücker, S. and Salehi, M. and Bergner, G. and Schütz, M. and Ströbel, P. and Marx, A. and Petersen, I. and Dietzek, B. and Popp, J.
    Analytical Chemistry 83 7081-7085 (2011)
    Immunohistochemistry (IHC) is one of the most widely used staining techniques for diagnostic purposes. The selective localization of target proteins in tissue specimens by conventional IHC is achieved with dye- or enzyme-labeled antibodies in combination with light microscopy. In this contribution, we demonstrate the proof-of-principle for IHC based on surface-enhanced coherent Raman scattering for contrast generation. Specifically, antibody-labeled metallic nanoshells in conjunction with surface-enhanced coherent anti-Stokes Raman scattering (SECARS) microscopy are employed for the selective, sensitive, and rapid localization of the basal cell protein p63 in normal prostate tissue. Negative control experiments were performed in order to confirm the selective binding of the target-specific metal nanoprobes and to disentangle the role of plasmonic (metal) and molecular (Raman reporter) resonances in this plasmon-assisted four-wave mixing technique. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/ac201284d
  • 2011 • 14 Hydrophilically stabilized gold nanostars as SERS labels for tissue imaging of the tumor suppressor p63 by immuno-SERS microscopy
    Schütz, M. and Steinigeweg, D. and Salehi, M. and Kömpe, K. and Schlücker, S.
    Chemical Communications 47 4216-4218 (2011)
    A biocompatible, seed-mediated synthesis of monodisperse ∼60 nm gold nanostars, followed by hydrophilic stabilization with ethylene glycol-modified Raman reporter molecules, is presented. Their application as SERS labels for imaging of the tumor suppressor p63 in prostate biopsies by immuno-SERS microscopy is demonstrated. © 2011 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c0cc05229a
  • 2011 • 13 Fast and cost-effective purification of gold nanoparticles in the 20-250 nm size range by continuous density gradient centrifugation
    Steinigeweg, D. and Schütz, M. and Salehi, M. and Schlücker, S.
    Small 7 2443-2448 (2011)
    A multilayer quasi-continuous density gradient centrifugation method for separating 20-250 nm metal colloids with high size resolution while maintaining particle stability is presented. Colloidal mixtures containing monodisperse gold nanospheres and clusters thereof, in particular, gold dimers, are purified with yields up to 94%. The rapid method uses standard laboratory equipment. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201100663
  • 2011 • 12 Hydrogen production from formic acid decomposition at room temperature using a Ag-Pd core-shell nanocatalyst
    Tedsree, K. and Li, T. and Jones, S. and Chan, C.W.A. and Yu, K.M.K. and Bagot, P.A.J. and Marquis, E.A. and Smith, G.D.W. and Tsang, S.C.E.
    Nature Nanotechnology 6 302-307 (2011)
    Formic acid (HCOOH) has great potential as an in situ source of hydrogen for fuel cells, because it offers high energy density, is non-toxic and can be safely handled in aqueous solution. So far, there has been a lack of solid catalysts that are sufficiently active and/or selective for hydrogen production from formic acid at room temperature. Here, we report that Ag nanoparticles coated with a thin layer of Pd atoms can significantly enhance the production of H 2 from formic acid at ambient temperature. Atom probe tomography confirmed that the nanoparticles have a core-shell configuration, with the shell containing between 1 and 10 layers of Pd atoms. The Pd shell contains terrace sites and is electronically promoted by the Ag core, leading to significantly enhanced catalytic properties. Our nanocatalysts could be used in the development of micro polymer electrolyte membrane fuel cells for portable devices and could also be applied in the promotion of other catalytic reactions under mild conditions. © 2011 Macmillan Publishers. All rights reserved.
    view abstractdoi: 10.1038/nnano.2011.42
  • 2010 • 11 Synthesis and catalytic properties of metal nanoparticles: Size, shape, support, composition, and oxidation state effects
    Cuenya, B.R.
    Thin Solid Films 518 3127-3150 (2010)
    Exciting new opportunities are emerging in the field of catalysis based on nanotechnology approaches. A new understanding and mastery of catalysis could have broad societal impacts, since about 80% of the processes in the chemical industry depend on catalysts to work efficiently. Efforts in surface science have led to the discovery of new heterogeneous catalysts, however, until recently the only way to develop new or improved catalysts was by empirical testing in trial-and-error experiments. This time-consuming and costly procedure is now rapidly being replaced by rational design methods that utilize fundamental knowledge of catalysts at the nanoscale. The advent of nanoscience and nanotechnology is providing the ability to create controlled structures and geometries to investigate and optimize a broad range of catalytic processes. As a result, researchers are obtaining fundamental insight into key features that influence the activity, selectivity, and lifetime of nanocatalysts. This review article examines several new findings as well as current challenges in the field of nanoparticle based catalysis, including the role played by the particle structure and morphology (size and shape), its chemical composition and oxidation state, and the effect of the cluster support. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2010.01.018
  • 2010 • 10 Magnetic alloy nanoparticles from laser ablation in cyclopentanone and their embedding into a photoresist
    Jakobi, J. and Petersen, S. and Menéndez-Manjón, A. and Wagener, P. and Barcikowski, S.
    Langmuir 26 6892-6897 (2010)
    The generation of nonoxidized magnetic alloy nanoparticles is still a challenge using conventional chemical reduction methods. However, because these nanoparticles are currently attracting much attention, alternative methods are required. In this context, the applicability of femtosecond laser ablation, which has evolved as a powerful tool for the generation of colloidal metal nanoparticles, has been investigated using the example of Ni48Fe 52 and Sm2Co17 ablation in cyclopentanone. Besides stability and size measurements, the focus has been placed on the analysis of the elemental composition of nanoparticles, which proved the preservation of the stoichiometry of the target in Ni-Fe nanoparticles but not in Sm-Co. It is assumed that this is due to a greater difference in the heat of evaporation of the bulk alloy components in Sm-Co than in Ni-Fe. Hence, the successful generation of magnetic alloy nanoparticles is possible for alloys composed of elements with similar heats of evaporation. This one-step approach allows the fabrication of nanomagnetic polymer composites (e.g., with application prospects in microtechnology such as microactuators). © 2010 American Chemical Society.
    view abstractdoi: 10.1021/la101014g
  • 2010 • 9 Quantitative visualization of colloidal and intracellular gold nanoparticles by confocal microscopy
    Klein, S. and Petersen, S. and Taylor, U. and Rath, D. and Barcikowski, S.
    Journal of Biomedical Optics 15 (2010)
    Gold nanoparticles (AuNPs) have the potential to become a versatile biomarker. For further use of AuNPs labeled with functionalized molecules, their visualization in biological systems by routine laboratory tools such as light microscopy is crucial. However, the size far below the diffraction limit affords specialized parameters for microscopical detection, which stimulated the current study, aimed to determine from which size onward AuNPs, either in dispersion or cell-associated, can be reliably detected by standard confocal microscopy. First, gold colloids of size-restricted fractions are examined in dispersion. At a minimum particle size of 60 nm, detection appears to be reliable. Particle counts in dilution series confirm these results by revealing single particle detection of 60-nm colloids. Second, AuNPs are visualized and quantified in cells, which interestingly cause a phase shift in the reflection of AuNPs. Gold mass spectroscopy confirms the number of AuNPs counted microscopically inside cells. Furthermore, it demonstrates for the first time a very high diffusion rate of 15-nm particles into the cells. In conclusion, the results back the suitability of confocal microscopy for the quantitative tracking of colloidal and intracellular gold nanoparticles sized 60 nm. © 2010 Society of Photo-Optical Instrumentation Engineers.
    view abstractdoi: 10.1117/1.3461170
  • 2010 • 8 Electrochemical synthesis of core-shell catalysts for electrocatalytic applications
    Kulp, C. and Chen, X. and Puschhof, A. and Schwamborn, S. and Somsen, C. and Schuhmann, W. and Bron, M.
    ChemPhysChem 11 2854-2861 (2010)
    A novel electrochemical method to prepare platinum shells around carbon-supported metal nanoparticles (Ru and Au) by pulsed electrodeposition from solutions containing Pt ions is presented. Shell formation is confirmed by characteristic changes in the cyclic voltammograms, and is further evidenced by monitoring particle growth by transmission electron microscopy as well as by energy-dispersive analysis of X rays (EDX). Scanning electrochemical microscopy and EDX measurements indicate a selective Pt deposition on the metal/carbon catalyst, but not on the glassy carbon substrate. The thus prepared carbon-supported core-shell nanoparticles are investigated with regard to their activity in electrocatalytic oxygen reduction, which demonstrates the applicability of these materials in electrocatalysis or sensors. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.200900881
  • 2010 • 7 Micro- and nanopatterning of functional organic monolayers on oxide-free silicon by laser-induced photothermal desorption
    Scheres, L. and Klingebiel, B. and Ter Maat, J. and Giesbers, M. and De Jong, H. and Hartmann, N. and Zuilhof, H.
    Small 6 1918-1926 (2010)
    The photothermal laser patterning of functional organic monolayers, prepared on oxide-free hydrogen-terminated silicon, and subsequent backfi lling of the laser-written lines with a second organic monolayer that differs in its terminal functionality, is described. Since the thermal monolayer decomposition process is highly nonlinear in the applied laser power density, subwavelength patterning of the organic monolayers is feasible. After photothermal laser patterning of hexadecenyl monolayers, the lines freed up by the laser are backfi lled with functional acid fl uoride monolayers. Coupling of cysteamine to the acid fl uoride groups and subsequent attachment of Au nanoparticles allows easy characterization of the functional lines by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Depending on the laser power and writing speed, functional lines with widths between 1.1 μm and 250 nm can be created. In addition, trifl uoroethyl-terminated (TFE) monolayers are also patterned. Subsequently, the decomposed lines are backfi lled with a nonfunctional hexadecenyl monolayer, the TFE stripes are converted into thiol stripes, and then finally covered with Au nanoparticles. By reducing the lateral distance between the laser lines, Au-nanoparticle stripes with widths close to 100 nm are obtained. Finally, in view of the great potential of this type of monolayer in the fi eld of biosensing, the ease of fabricating biofunctional patterns is demonstrated by covalent binding of fl uorescently labeled oligo-DNA to acidfl uoride-backfi lled laser lines, which-as shown by fl uorescence microscopy-is accessible for hybridization.Copyright © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201000189
  • 2010 • 6 SERS Microscopy: Nanoparticle Probes and Biomedical Applications
    Schlücker, S.
    Surface Enhanced Raman Spectroscopy: Analytical, Biophysical and Life Science Applications 263-283 (2010)
    doi: 10.1002/9783527632756.ch12
  • 2010 • 5 Platinum nanoparticles: The crucial role of crystal face and colloid stabilizer in the diastereoselective hydrogenation of cinchonidine
    Schmidt, E. and Kleist, W. and Krumeich, F. and Mallat, T. and Baiker, A.
    Chemistry - A European Journal 16 2181-2192 (2010)
    The preparation of stable metal nanoparticles requires a strong interaction between the (organic) stabilizer and the metal surface that might alter the catalytic properties. This behavior has been described as "poisoning" since the stabilizer normally decreases the catalytic activity due to site blocking. Here we show a striking influence of the stabilizer on the selectivity in the hydrogenation of cinchonidine (CD) over poly(acrylic acid) (PAA)-stabilized Pt nanoparticles with well-defined shape distributions. In the hydrogenation of the heteroaromatic ring of cinchonidine in toluene, the diastereomeric excess of the (S)-hexahydrocinchonidine increased upon increasing Pt{111}/Pt{100} ratio, but this distinct shape selectivity was observed only after the oxidative removal of PAA at 473 K. The use of the as-prepared nanoparticles inverted the major diastereomer to R, and this isomer was formed also in acetic acid. This striking change in the diastereoselectivity indicates that poly(acrylic acid), which remains on the Pt surface after preparation, interacts with CD during hydrogenation almost as strongly as the solvent acetic acid. The PAA stabilizer plays a dual role: it allows one to control the size and shape of the nanoparticles during their synthesis, and it affects the rate and diastereoselectivity of the hydrogenation of CD probably through a "surface-localized acidification". © 2010 Wiley-VCH Verlag GmbH & Co. KGaA,.
    view abstractdoi: 10.1002/chem.200902517
  • 2010 • 4 Synthesis of glass-coated SERS nanoparticle probes via SAMs with terminal SiO2 precursors
    Schütz, M. and Küstner, B. and Bauer, M. and Schmuck, C. and Schlücker, S.
    Small 6 733-737 (2010)
    A short synthesis route to silica-encapsulated nanoparticles coated with a self-assembled monolayer (SAM) is presented. The organic molecules within the SAM contain a SiO2 precursor to render the surface vitreophilic. Due to the high mechanical and chemical stability of a glass shell, such particles can be used as probes in targeted research with surface-enhanced Raman scattering as the read-out method. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.200902065
  • 2010 • 3 Nonendosomal cellular uptake of ligand-free, positively charged gold nanoparticles
    Taylor, U. and Klein, S. and Petersen, S. and Kues, W. and Barcikowski, S. and Rath, D.
    Cytometry Part A 77 439-446 (2010)
    Gold nanoparticles (GNPs) have interesting optical properties, such as exceptionally high quantum yields and virtually limitless photostability. Therefore, they show the potential for applications as biomarkers especially suitable for in vivo and long-term studies. The generation of GNPs using pulsed laser light rather than chemical means provides nanoparticles, which are remarkably stable in a variety of media without the need of stabilizing agents or ligands. This stabilization is achieved by partial oxidation of the gold surface resulting in positively charged GNPs. However, little is known about cellular uptake of such ligand-free nanoparticles, their intracellular fate, or cell viability after nanoparticle contact. The current work is aimed to explore the response of a bovine cell line to GNP exposure mainly using laser scanning confocal microscopy (LSCM) supported by other techniques. Cultured bovine immortalized cells (GM7373) were coincubated with GNP (average diameter 15 nm, 50 μM Au) for 2, 24, and 48 h. The detection of GNP-associated light scattering by the LSCM facilitated a clear distinction between GNP-containing cells and the negative controls. After 48 h, 75% of cells had visibly incorporated nanoparticles. No colocalization was detected with either Rab5a or Lamp1-positive structures, i.e., endosomes or lysosomes, respectivley. However, transmission electron microscope analysis of GNP-coincubated cells indicated the nanoparticles to be positioned within electron-dense structures. Coincubation at 4°C did not inhibit nanoparticle uptake, suggesting diffusion as possible entrance mechanism. Although the assessment of cell morphology, membrane integrity, and apoptosis revealed no GNP-related loss of cell viability at a gold concentration of 25 μM or below, a cytotoxic effect was observed in a proliferation assay after exposing low cell numbers to 50 μM Au and above. In conclusion, this study confirmed the cellular uptake of ligand-free gold nanoparticles during coincubation apparently without using endocytic pathways. © 2010 International Society for Advancement of Cytometry.
    view abstractdoi: 10.1002/cyto.a.20846
  • 2010 • 2 The influence of surface composition of nanoparticles on their interactions with serum albumin
    Treuel, L. and Malissek, M. and Gebauer, J.S. and Zellner, R.
    ChemPhysChem 11 3093-3099 (2010)
    Interactions between differently functionalised silver and gold nanoparticles (NPs) as well as polystyrene nanoparticles with bovine serum albumin (BSA) are studied using circular dichroism (CD) spectroscopy. It is found that the addition of NPs to the protein solution destroys part of the helical secondary structure of the protein as a result of surface adsorption. From the loss of free protein and hence the extent of their structural change adsorption equilibrium constants are derived. The results reveal that citrate-coated gold and silver NPs exhibit much stronger interactions with BSA than polymeric or polymer-coated metallic NPs. It is therefore concluded that for the particles considered, the influence of surface composition on the interaction behaviour dominates that of the core. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cphc.201000174
  • 2010 • 1 Wear mechanisms in metal-on-metal bearings: The importance of tribochemical reaction layers
    Wimmer, M.A. and Fischer, A. and Büscher, R. and Pourzal, R. and Sprecher, C. and Hauert, R. and Jacobs, J.J.
    Journal of Orthopaedic Research 28 436-443 (2010)
    Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/jor.21020