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 • 178 Effect of the bias voltage on the structural and tribo-mechanical properties of Ag-containing amorphous carbon films
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D. and Nienhaus, A. and Thomann, C.A. and Wittrock, A. and Moldenhauer, H. and Debus, J.
    Diamond and Related Materials 105 (2020)
    The modification of amorphous carbon films by a mixture of Ag atoms is a promising approach to reduce the residual stresses in the coating and to improve its adhesion to the substrate. Besides the Ag concentration, the bias voltage has a crucial impact on the properties of carbon-based films. Therefore, the effect of the bias voltage on the structural and tribo-mechanical properties of hydrogen free a-C:Ag is investigated. The a-C:Ag films are sputtered from graphite targets with varying number of Ag pellets by setting the bias voltage to −100, −150, and −200 V. A non-modified a-C and two a-C:Ag film systems with different Ag content are synthetized to obtain a comprehensive understanding about the influence of the bias voltage on the properties of the a-C:Ag films. A high bias voltage leads to a reduction in the amount of Ag within the a-C:Ag films, since impinging ions remove Ag atoms during the film growth. Additionally, XRD analyses show the formation of large Ag nanocrystallites with rising bias voltage. In Raman scattering studies, an Ag-induced graphitization of the a-C films is identified. The graphitization is less pronounced at low Ag concentrations and high bias voltages. The residual stresses increase with rising bias voltage and decreasing Ag content, which also favor greater values of hardness and elastic modulus. While a high bias voltage results in a poor adhesion strength for the a-C films, a good adhesion behavior is observed for the a-C:Ag films. It is ascribed to lower stresses in the a-C:Ag films as compared to that in a-C. The friction behavior of the a-C:Ag films is not influenced by the bias voltage, since the coefficients of friction vary from 0.26 to 0.32 against a steel counterpart in tribometer tests. An agglomeration of Ag particles in the tribological contact is observed for all a-C:Ag films which contributes to the slightly higher friction when compared to non-modified a-C films. On the whole, it is demonstrated that the tribo-mechanical properties of a-C:Ag are not only affected by the Ag content, but also by the applied bias voltage. © 2020 Elsevier B.V.
    view abstractdoi: 10.1016/j.diamond.2020.107803
  • 2019 • 177 Functionalization of titania nanotubes with electrophoretically deposited silver and calcium phosphate nanoparticles: Structure, composition and antibacterial assay
    Chernozem, R.V. and Surmeneva, M.A. and Krause, B. and Baumbach, T. and Ignatov, V.P. and Prymak, O. and Loza, K. and Epple, M. and Ennen-Roth, F. and Wittmar, A. and Ulbricht, M. and Chudinova, E.A. and Rijavec, T. and Lapanje, A...
    Materials Science and Engineering C 97 420-430 (2019)
    Herein TiO2 nanotubes (NTs) were fabricated via electrochemical anodization and coated with silver and calcium phosphate (CaP) nanoparticles (NPs) by electrophoretic deposition. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ag and CaP NPs were successfully deposited onto the TiO2 NTs. Using X-ray diffraction, only anatase and Ti were observed after deposition of Ag and CaP NPs. However, X-ray photoelectron spectroscopy (XPS) analysis revealed that the binding energy (BE) of the Ag and CaP NP core levels corresponded to metallic Ag, hydroxyapatite and amorphous calcium phosphate, based on the knowledge that CaP NPs synthesized by precipitation have the nanocrystalline structure of hydroxyapatite. The application of Ag NPs allows for decreasing the water contact angle and thus increasing the surface free energy. It was concluded that the CaP NP surfaces are superhydrophilic. A significant antimicrobial effect was observed on the TiO2 NT surface after the application of Ag NPs and/or CaP NPs compared with that of the pure TiO2 NTs. Thus, fabrication of TiO2 NTs, Ag NPs and CaP NPs with PEI is promising for diverse biomedical applications, such as in constructing a biocompatible coating on the surface of Ti that includes an antimicrobial effect. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2018.12.045
  • 2019 • 176 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/j.dental.2019.06.003
  • 2019 • 175 Plasmon Enhanced Two-Photon Probing with Gold and Silver Nanovoid Structures
    Madzharova, F. and Öhl, D. and Junqueira, J. and Schuhmann, W. and Kneipp, J.
    Advanced Optical Materials 7 (2019)
    Nonlinear optical signals benefit greatly from the enhanced local optical fields in the vicinity of plasmonic nanostructures. Gold and silver nanovoid arrays of varying size and thickness, fabricated by electrochemical deposition are shown here to act as stable plasmonic nanostructures and to enhance the weak, incoherent two-photon excited process of surface-enhanced hyper Raman scattering (SEHRS) with high microscopic homogeneity and reproducibility that typical SEHRS experiments have not been addressing so far. Silver nanovoids yield stronger enhancement than gold voids, but gold nanovoid arrays show improved stability at high laser excitation intensities. Combined screening experiments using SEHRS and second-harmonic generation (SHG) reveal a dependence of the enhancement of both signals on void structural parameters and similar optimum geometries for both two-photon processes. The results confirm the suggested important role for the enhancement of the near-infrared excitation field in SEHRS and suggest SHG as a fast screening tool to identify nanostructures that can support high SEHRS enhancement. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adom.201900650
  • 2019 • 174 Influence of Ag on antibacterial performance, microstructure and phase transformation of NiTi shape memory alloy coatings
    Momeni, S. and Tillmann, W.
    Vacuum 164 242-245 (2019)
    Shape memory binary NiTi and ternary NiTiAg coatings were deposited by means of magnetron sputtering technique. The results show how simultaneous sputtering of Ag can affect the microstructure, phase transformation behavior and antibacterial properties of NiTi coatings. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.vacuum.2019.02.051
  • 2019 • 173 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 • 172 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
  • 2018 • 171 An N-Heterocyclic Carbene Based Silver Precursor for Plasma-Enhanced Spatial Atomic Layer Deposition of Silver Thin Films at Atmospheric Pressure
    Boysen, N. and Hasselmann, T. and Karle, S. and Rogalla, D. and Theirich, D. and Winter, M. and Riedl, T. and Devi, A.
    Angewandte Chemie - International Edition 57 16224-16227 (2018)
    A new N-heterocyclic carbene (NHC)-based silver amide compound, 1,3-di-tert-butyl-imidazolin-2-ylidene silver(I) 1,1,1-trimethyl-N-(trimethylsilyl)silanaminide [(NHC)Ag(hmds)] was synthesized and analyzed by single-crystal X-ray diffraction, 1H and 13C NMR spectroscopy, as well as EI mass spectrometry, and subsequently evaluated for its thermal characteristics. This new halogen- and phosphine-free Ag atomic layer deposition (ALD) precursor was tested successfully for silver thin film growth in atmospheric pressure plasma enhanced spatial (APP-ALD). High-purity conductive Ag thin films with a low sheet resistance of 0.9 Ω/sq (resistivity: 10−5 Ωcm) were deposited at 100 °C and characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, optical transmittance, and Rutherford back-scattering techniques. The carbene-based Ag precursor and the new APP-ALD process are significant developments in the field of precursor chemistry as well as metal ALD processing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/anie.201808586
  • 2018 • 170 Peripheral Blood Plasma Clot as a Local Antimicrobial Drug Delivery Matrix
    Gessmann, J. and Seybold, D. and Ayami, F. and Peter, E. and Baecker, H. and Schildhauer, T.A. and Köller, M.
    Tissue Engineering - Part A 24 809-818 (2018)
    Platelet-free blood plasma clots were loaded either with antibiotics (vancomycin, gentamicin, or linezolid) at concentrations of 5-300 μg/mL or with silver ions (silver acetate) at concentrations of 3.3-129 μg/mL. The release of antibiotics or silver from the clot matrix was analyzed after repeated immersion of the plasma clots using reversed-phase high-performance liquid chromatography (RP-HPLC) or atomic absorption spectroscopy (AAS). The antimicrobial activity was tested against Staphylococcus aureus; tissue cell compatibility was analyzed using human mesenchymal stem cells (hMSC). Fibrin fiber thickness of the clots was analyzed by scanning electron microscopy. While addition of linezolid and vancomycin did not significantly change the fibrin fiber thickness, gentamicin and silver ions led to an increase in fiber thickness. All antibiotics showed a concentration-dependent burst-like release from the plasma clots within 1 h followed by a general decay in elution. The release of vancomycin and gentamicin, or silver lasted up to 7 days (depending on initial concentrations), but lasted only up to 4 h for linezolid. A correlation (p < 0.0001) was noted between the concentration of released antibiotics analyzed by HPLC and antimicrobial activity (agar diffusion test). A decrease in antibacterial activity of gentamicin- and vancomycin-containing clots occurred within 4 or 5 days. In contrast, the corresponding antibacterial activity of plasma clots containing linezolid was limited to 3 h. Antibacterial activity of plasma clots containing silver at the highest concentrations decreased after day 3, but clots with lower concentrations induced incomplete bacterial lysis or displayed no antibacterial activity. The antibiotic-containing clots did not induce cytotoxic effects on the embedded hMSC in contrast to all clots containing silver. Our results indicate that an autologous plasma clot can be used to deliver antibiotics such as vancomycin and gentamicin in combination with hMSC and the antibacterial effects persist for days without inducing cytotoxic effects on the embedded stem cells. © Copyright 2018, Mary Ann Liebert, Inc.
    view abstractdoi: 10.1089/ten.tea.2017.0319
  • 2018 • 169 Nano Impact Electrochemistry: Effects of Electronic Filtering on Peak Height, Duration and Area
    Kanokkanchana, K. and Saw, E.N. and Tschulik, K.
    ChemElectroChem 5 3000-3005 (2018)
    Nano impact electrochemistry is used to measure a transient signal while a nanoparticle (NP) hits an electrode due to its motion in a solution. A variety of information can be obtained from this current pulse, yet its accurate measurement is challenging due to its short duration (μs to s) and small amplitude (≤10 nA). A typically used low bandwidth low-pass filter can improve the signal-to-noise ratio, but it may cost severely in the accuracy of the data. Here, we demonstrate the effects of electronic filters by using generated current impulses with duration from 125 μs to 8 ms. Initially, a system dedicated to measure short and low current impulses was employed. There, an 8th order Bessel filter was used and the effect of varying the cut-off frequency between 50 Hz and 20 kHz on the impulse response is studied. Even though the charge is generally conserved by the filter, amplitude and duration of the pulse vary greatly in dependence of the cut-off frequency. In comparison, the response of widely used potentiostats was tested and significant deviations of the measured signal from the input were detected. Supported by destructive nano impact experiments with Ag NPs in KCl(aq), we show how the filtering affects the experimentally determined size of Ag NPs and Cl− diffusion coefficient, using impact charges and duration, respectively. As a result, we suggest a general guideline to researchers for accurate electrochemical nano impact measurements, in particular with respect to current peak duration analysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/celc.201800738
  • 2018 • 168 Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy
    Öhl, D. and Kayran, Y.U. and Junqueira, J.R.C. and Eßmann, V. and Bobrowski, T. and Schuhmann, W.
    Langmuir 34 12293-12301 (2018)
    Surface-enhanced Raman spectroscopy is a powerful analytical tool and a strongly surface structure-dependent process. Importantly, it can be coupled with electrochemistry to simultaneously record vibrational spectroscopic information during electrocatalytic reactions. Highest Raman enhancements are obtained using precisely tuned nanostructures. The fabrication and evaluation of a high number of different nanostructures with slightly different properties is time-consuming. We present a strategy to systematically determine optimal nanostructure properties of electrochemically generated Ag void structures in order to find the void size providing highest signal enhancement for Raman spectroscopy. Ag-coated Si wafers were decorated with a monolayer of differently sized polymer nanospheres using a Langmuir-Blodgett approach. Subsequently, bipolar electrochemistry was used to electrodeposit a gradient of differently sized void structures. The gradient structures were locally evaluated using Raman spectroscopy of a surface-adsorbed Raman probe, and the surface regions exhibiting the highest Raman enhancement were characterized by means of scanning electron microscopy. High-throughput scanning droplet cell experiments were utilized to determine suitable conditions for the electrodeposition of the found highly active structure in a three-electrode electrochemical cell. This structure was subsequently employed as the working electrode in operando surface-enhanced Raman measurements to verify its viability as the signal amplifier and to spectroscopically rationalize the complex electrochemical reduction of carbon dioxide. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.8b02501
  • 2018 • 167 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 • 166 Ag-Segregation to Dislocations in PbTe-Based Thermoelectric Materials
    Yu, Y. and Zhang, S. and Mio, A.M. and Gault, B. and Sheskin, A. and Scheu, C. and Raabe, D. and Zu, F. and Wuttig, M. and Amouyal, Y. and Cojocaru-Mirédin, O.
    ACS Applied Materials and Interfaces 10 3609-3615 (2018)
    Dislocations have been considered to be an efficient source for scattering midfrequency phonons, contributing to the enhancement of thermoelectric performance. The structure of dislocations can be resolved by electron microscopy whereas their chemical composition and decoration state are scarcely known. Here, we correlate transmission Kikuchi diffraction and (scanning) transmission electron microscopy in conjunction with atom probe tomography to investigate the local structure and chemical composition of dislocations in a thermoelectric Ag-doped PbTe compound. Our investigations indicate that Ag atoms segregate to dislocations with a 10-fold excess of Ag compared with its average concentration in the matrix. Yet the Ag concentration along the dislocation line is not constant but fluctuates from ∼0.8 to ∼10 atom % with a period of about 5 nm. Thermal conductivity is evaluated applying laser flash analysis, and is correlated with theoretical calculations based on the Debye-Callaway model, demonstrating that these Ag-decorated dislocations yield stronger phonon scatterings. These findings reduce the knowledge gap regarding the composition of dislocations needed for theoretical calculations of phonon scattering and pave the way for extending the concept of defect engineering to thermoelectric materials. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acsami.7b17142
  • 2017 • 165 Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications
    Cojocaru-Mirédin, O. and Abdellaoui, L. and Nagli, M. and Zhang, S. and Yu, Y. and Scheu, C. and Raabe, D. and Wuttig, M. and Amouyal, Y.
    ACS Applied Materials and Interfaces 9 14779-14790 (2017)
    Thermoelectric (TE) materials are of utmost significance for conversion of heat flux into electrical power in the low-power regime. Their conversion efficiency depends strongly on the microstructure. AgSbTe2-based compounds are high-efficiency TE materials suitable for the mid-temperature range. Herein, we explore an Ag16.7Sb30Te53.3 alloy (at %) subjected to heat treatments at 380 °C for different durations aimed at nucleation and coarsening of Sb2Te3-precipitates. To characterize the Sb2Te3-precipitation, we use a set of methods combining thermal and electrical measurements in concert with transmission electron microscopy and atom probe tomography. We find correlations between the measured TE transport coefficients and the applied heat treatments. Specifically, the lowest electrical and thermal conductivity values are obtained for the as-quenched state, whereas the highest values are observed for alloys aged for 8 h. In turn, long-term heat treatments result in intermediate values of transport coefficients. We explain these findings in terms of interplay between precipitate formation and variations in the matrix composition, highlighting the importance of thermal stability of the material under service conditions. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acsami.7b00689
  • 2017 • 164 Electron-induced photon emission above the quantum cutoff due to time-energy uncertainty
    Ekici, E. and Kapitza, P. and Bobisch, C.A. and Möller, R.
    Optics Letters 42 4585-4588 (2017)
    The light emission from a tunneling junction induced by tunneling electrons has been studied around the cutoff at hν eVt. The emitted photons are found to exceed the excitation energy provided by the energy of the tunneling electrons. The experiments have been performed by a low-temperature scanning tunneling microscope at 80 K for an Ag(111) surface and an Ag-covered PtIr tip. A detailed analysis of the emission spectra reveals that the findings cannot be explained by the thermal broadening of the electron Fermi distribution alone. However, a correct description is found if a finite lifetime of the excited states in the range of 30–80 fs is included. © 2017 Optical Society of America.
    view abstractdoi: 10.1364/OL.42.004585
  • 2017 • 163 A Unified Interdisciplinary Approach to Design Antibacterial Coatings for Fast Silver Release
    El Arrassi, A. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Köller, M. and Ludwig, Al. and Tschulik, K.
    ChemElectroChem (2017)
    The increasing number of surgical treatments performed per year requires novel approaches to inhibit implant-associated infections, caused by multi-antibiotic resistant bacteria. Silver ions (Ag+) are known for their effective antimicrobial activity. Therefore, a system that efficiently and locally releases the minimum required amount of Ag+ directly after the surgical treatment is in high demand. Herein we study electrochemically, microbiologically, microscopically and spectroscopically sacrificial Ag anode coatings for antibacterial implant applications. It is found that Ag dot arrays deposited on noble metals (Pd, Ir) release Ag+ much faster than continuous Ag thin films. The Ag+ release qualitatively scales with the difference of standard potentials between Ag and the noble metal. Furthermore, with higher numbers of Ag dots, the total amount of released Ag+ increases, while the release efficiency declines. Notably, an efficient killing of Staphylococcus aureus bacteria was seen for coatings containing as little as 23ng of Ag per mm2. Thus, the use of sacrificial Ag anodes as highly efficient antibacterial coating materials is evaluated. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201700247
  • 2017 • 162 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 • 161 Antibacterial activity of microstructured sacrificial anode thin films by combination of silver with platinum group elements (platinum, palladium, iridium)
    Köller, M. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Tschulik, K. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 74 536-541 (2017)
    Five different Ag dots arrays (16 to 400dots/mm2) were fabricated on a continuous platinum, palladium, or iridium thin film and for comparison also on titanium film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Staphylococcus aureus (S. aureus) were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards . S. aureus was induced by Ag dot arrays on each of the platinum group thin film (sacrificial anode system for Ag) in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag). Among platinum group elements the Ir-Ag system exerted the highest antibacterial activity which was accompanied by most advanced dissolution of the Ag dots and Ag ion release compared to Ag dots on Pt or Pd. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.msec.2016.12.075
  • 2017 • 160 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 • 159 Combinatorial screening of Pd-based quaternary electrocatalysts for oxygen reduction reaction in alkaline media
    Li, J. and Stein, H.S. and Sliozberg, K. and Liu, J. and Liu, Y. and Sertic, G. and Scanley, E. and Ludwig, Al. and Schroers, J. and Schuhmann, W. and Taylor, A.D.
    Journal of Materials Chemistry A 5 67-72 (2017)
    The implementation of electrochemical systems such as fuel cells has been hindered by the slow development of low cost high activity catalysts. Here we examine the oxygen reduction reaction performance of a combinatorial Pd-Au-Ag-Ti thin film library using high-throughput screening and correlate the electrochemical behavior to the crystallographic properties. We find compositions of ca. 40-60 at% Pd and 30-35 at% Au exhibit both a low overpotential of close to the value of pure Pt as well as high current density. We also observe a volcano-like relationship between the overpotential and the solid formation strain. This study provides compositional guidance towards the future synthesis of nanostructured quaternary Pd-Au-Ag-Ti alloys and suggests the potential for broader application of high-throughput electrochemical characterization by means of an automatic scanning droplet cell. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/C6TA08088J
  • 2017 • 158 The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface
    Morbec, J.M. and Kratzer, P.
    Journal of Chemical Physics 146 (2017)
    Using first-principles calculations based on density-functional theory (DFT), we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that “pure” DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to the experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4973839
  • 2017 • 157 Thermo-mechanical stresses within switching contact systems after arcing events
    Mutzel, T. and Ma, D. and Roters, F. and Raabe, D.
    Electrical Contacts, Proceedings of the Annual Holm Conference on Electrical Contacts 145-151 (2017)
    Silver tin oxide (Ag/SnO2) contact materials are widely used in contactor applications. A general trend in this application field is the steadily ongoing miniaturization of switching devices, resulting in growing energy densities to be handled by the contact system. The higher arcing energy densities in such new designs are inducing increased thermo-mechanical stresses in the contact system. As these stresses cannot be measured, FEM simulation was applied to make them visible for heavy duty break arcs. Focus of the presented studies is the temperature dependent elastic and plastic modeling of the intermediate Ag layer and the braze filler. Based on these simulations, improvements in material stress behavior of the complete system (sub-assembly) should be realized. © 2017 IEEE.
    view abstractdoi: 10.1109/HOLM.2017.8088077
  • 2017 • 156 Interfacial hydrogen localization in austenite/martensite dual-phase steel visualized through optimized silver decoration and scanning Kelvin probe force microscopy
    Nagashima, T. and Koyama, M. and Bashir, A. and Rohwerder, M. and Tasan, C.C. and Akiyama, E. and Raabe, D. and Tsuzaki, K.
    Materials and Corrosion 68 306-310 (2017)
    The hydrogen distribution in an austenite-martensite dual-phase steel was investigated using silver decoration and scanning Kelvin probe force microscopy. The silver decoration technique optimized for spacial resolution reveals interfacial segregation of hydrogen along the plate-type martensite-martensite grain boundaries. In addition, the scanning Kelvin probe force microscopy kinetically elucidates that hydrogen preferentially diffused out from the martensite-martensite grain boundaries. These preferential sites of hydrogen desorption correspond to the regions of hydrogen-assisted damage. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/maco.201609104
  • 2017 • 155 Pulsed laser ablation in liquids: Impact of the bubble dynamics on particle formation
    Reich, S. and Schönfeld, P. and Wagener, P. and Letzel, A. and Ibrahimkutty, S. and Gökce, B. and Barcikowski, S. and Menzel, A. and dos Santos Rolo, T. and Plech, A.
    Journal of Colloid and Interface Science 489 106-113 (2017)
    Pulsed laser ablation in liquids (PLAL) is a multiscale process, involving multiple mutually interacting phenomena. In order to synthesize nanoparticles with well-defined properties it is important to understand the dynamics of the underlying structure evolution. We use visible-light stroboscopic imaging and X-ray radiography to investigate the dynamics occurring during PLAL of silver and gold on a macroscopic scale, whilst X-ray small angle scattering is utilized to deepen the understanding on particle genesis. By comparing our results with earlier reports we can elucidate the role of the cavitation bubble. We find that symmetry breaking at the liquid-solid interface is a critical factor for bubble motion and that the bubble motion acts on the particle distribution as confinement and retraction force to create secondary agglomerates. © 2016 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2016.08.030
  • 2017 • 154 Fluence Threshold Behaviour on Ablation and Bubble Formation in Pulsed Laser Ablation in Liquids
    Reich, S. and Schönfeld, P. and Letzel, A. and Kohsakowski, S. and Olbinado, M. and Gökce, B. and Barcikowski, S. and Plech, A.
    ChemPhysChem 18 1084-1090 (2017)
    The ablation yield and bubble-formation process during nanosecond pulsed-laser ablation of silver in water are analysed by stroboscopic videography, time-resolved X-ray radiography and in situ UV/Vis spectroscopy. This process is studied as function of lens–target distance and laser fluence. Both the ablation yield and the bubble-cavitation process exhibit threshold behaviour as a function of fluence, which is linked to the efficiency of coupling of energy at the water/target interface. Although ablation happens below this threshold, quantitative material emission is linked to bubble formation. Above the threshold, both bubble size and ablation show linear behaviour. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cphc.201601198
  • 2017 • 153 Time-resolved impact electrochemistry for quantitative measurement of single-nanoparticle reaction kinetics
    Saw, E.N. and Kratz, M. and Tschulik, K.
    Nano Research 1-10 (2017)
    Single-nanoparticle electrochemistry has been established as a tool to characterize various nanomaterials based on the charge passed during their random impact at an electrode. Here it is demonstrated that the duration and shape of the resulting current peak can be used to quantify the reaction kinetics on a single-particle basis. Both the chemical rate constant and reaction mechanism for oxidation of single nanoparticles in different electrolytes can be determined directly from the duration of the current signal recorded in high-speed, highsensitivity current measurements. Using 29-nm-sized Ag particles in four different electrolytes as a proof of concept for this general approach, hitherto inaccessible insights into single-particle reactivity are provided. While comparable rate constants were measured for the four electrolytes at low overpotentials, transport-limited impacts at high overpotentials were found to depend strongly on the type and quantity of anions present in solution. [Figure not available: see fulltext.] © 2017 Tsinghua University Press and Springer-Verlag GmbH Germany
    view abstractdoi: 10.1007/s12274-017-1578-3
  • 2017 • 152 Local characterization of light trapping effects of metallic and dielectric nanoparticles in ultra-thin Cu(In,Ga)Se2 solar cells via scanning near-field optical microscopy
    Song, M. and Yin, G. and Fumagalli, P. and Schmid, M.
    Proceedings of SPIE - The International Society for Optical Engineering 10114 (2017)
    Plasmonic and photonic nanoparticles have proven beneficial for solar cells in the aspect of light management. For improved exploitation of nanoparticles in solar cells, it is necessary to reveal the absorption enhancement mechanism from the nanoparticles. In this study, we investigated the nanoparticle-enhanced solar cells in near-field regime with optic and opto-electric scanning near-field optical microscopy (SNOM). The near-field distribution of regularly arranged silver and polystyrene nanoparticles produced by nanosphere lithography on Cu(In,Ga)Se2 (CIGSe) solar cells is characterized using a custom-built SNOM, which gives insight into the optical mechanism of light trapping from nanoparticles to solar cells. On the other hand, the photocurrent of CIGSe solar cells with and without nanoparticles is studied with an opto-electric SNOM by recording the photocurrent during surface scanning, further revealing the opto-electrical influences of the nanoparticles. In addition, finite element method simulations have been performed and agree with the results from SNOM. We found the dielectric polystyrene spheres are able to enhance the absorption and benefit the generation of charge carriers in the solar cells. Copyright © 2017 SPIE.
    view abstractdoi: 10.1117/12.2253223
  • 2017 • 151 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 • 150 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 • 149 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 • 148 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
  • 2016 • 147 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 • 146 Scalable and Environmentally Benign Process for Smart Textile Nanofinishing
    Feng, J. and Hontañón, E. and Blanes, M. and Meyer, J. and Guo, X. and Santos, L. and Paltrinieri, L. and Ramlawi, N. and Smet, L.C.P.M.D. and Nirschl, H. and Kruis, F.E. and Schmidt-Ott, A. and Biskos, G.
    ACS Applied Materials and Interfaces 8 14756-14765 (2016)
    A major challenge in nanotechnology is that of determining how to introduce green and sustainable principles when assembling individual nanoscale elements to create working devices. For instance, textile nanofinishing is restricted by the many constraints of traditional pad-dry-cure processes, such as the use of costly chemical precursors to produce nanoparticles (NPs), the high liquid and energy consumption, the production of harmful liquid wastes, and multistep batch operations. By integrating low-cost, scalable, and environmentally benign aerosol processes of the type proposed here into textile nanofinishing, these constraints can be circumvented while leading to a new class of fabrics. The proposed one-step textile nanofinishing process relies on the diffusional deposition of aerosol NPs onto textile fibers. As proof of this concept, we deposit Ag NPs onto a range of textiles and assess their antimicrobial properties for two strains of bacteria (i.e., Staphylococcus aureus and Klebsiella pneumoniae). The measurements show that the logarithmic reduction in bacterial count can get as high as ca. 5.5 (corresponding to a reduction efficiency of 99.96%) when the Ag loading is 1 order of magnitude less (10 ppm; i.e., 10 mg Ag NPs per kg of textile) than that of textiles treated by traditional wet-routes. The antimicrobial activity does not increase in proportion to the Ag content above 10 ppm as a consequence of a "saturation" effect. Such low NP loadings on antimicrobial textiles minimizes the risk to human health (during textile use) and to the ecosystem (after textile disposal), as well as it reduces potential changes in color and texture of the resulting textile products. After three washes, the release of Ag is in the order of 1 wt %, which is comparable to textiles nanofinished with wet routes using binders. Interestingly, the washed textiles exhibit almost no reduction in antimicrobial activity, much as those of as-deposited samples. Considering that a realm of functional textiles can be nanofinished by aerosol NP deposition, our results demonstrate that the proposed approach, which is universal and sustainable, can potentially lead to a wide number of applications. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acsami.6b03632
  • 2016 • 145 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 • 144 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 • 143 The Electrochemical Characterization of Single Core-Shell Nanoparticles
    Holt, L.R. and Plowman, B.J. and Young, N.P. and Tschulik, K. and Compton, R.G.
    Angewandte Chemie - International Edition 55 397-400 (2016)
    We report the direct solution-phase characterization of individual gold-core silver-shell nanoparticles through an electrochemical means, with selectivity achieved between the core and shell components based on their different redox activities. The electrochemically determined core-shell sizes are in excellent agreement with electron microscopy-based results, successfully demonstrating the electrochemical characterization of individual core-shell nanoparticles. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/anie.201509008
  • 2016 • 142 Fabrication and physico-mechanical properties of thin magnetron sputter deposited silver-containing hydroxyapatite films
    Ivanova, A.A. and Surmeneva, M.A. and Tyurin, A.I. and Pirozhkova, T.S. and Shuvarin, I.A. and Prymak, O. and Epple, M. and Chaikina, M.V. and Surmenev, R.A.
    Applied Surface Science 360 929-935 (2016)
    As a measure of the prevention of implant associated infections, a number of strategies have been recently applied. Silver-containing materials possessing antibacterial activity as expected might have wide applications in orthopedics and dentistry. The present work focuses on the physico-chemical characterization of silver-containing hydroxyapatite (Ag-HA) coating obtained by radio frequency (RF) magnetron sputtering. Mechanochemically synthesized Ag-HA powder (Ca10-xAgx(PO4)6(OH)2-x, x = 1.5) was used as a precursor for sputtering target preparation. Morphology, composition, crystallinity, physico-mechanical features (Young's modulus and nanohardness) of the deposited Ag-HA coatings were investigated. The sputtering of the nanostructured multicomponent target at the applied process conditions allowed to deposit crystalline Ag-HA coating which was confirmed by XRD and FTIR data. The SEM results revealed the formation of the coating with the grain morphology and columnar cross-section structure. The EDX analysis confirmed that Ag-HA coating contained Ca, P, O and Ag with the Ca/P ratio of 1.6 ± 0.1. The evolution of the mechanical properties allowed to conclude that addition of silver to HA film caused increase of the coating nanohardness and elastic modulus compared with those of pure HA thin films deposited under the same deposition conditions. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.11.087
  • 2016 • 141 Rigorous analysis of light scattering by a grating of nanocylinders coupled to a dielectric substrate
    Jandieri, V. and Yasumoto, K. and Erni, D.
    2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016 545-548 (2016)
    Light scattering by a grating made of the Ag nanocylinders onto a dielectric substrate is investigated using an accurate and rigorous formalism based on a recursive algorithm combined with the lattice sums technique. Physical insight is given to the localization of the field along the interfaces of the Ag nanocylinders, to the strong reflected field by the grating and the field enhancement at the surface of the dielectric substrate. The accuracy of the numerical analysis has been validated based on the principle of the energy conservation. © 2016 IEEE.
    view abstractdoi: 10.1109/URSI-EMTS.2016.7571450
  • 2016 • 140 Effect of various dispersing agents on the stability of silver microparticle dispersion and the formulation of uniform silver film by laser melting
    Letzel, A. and Maurer, E. and Meixner, M. and Poprawe, R. and Stollenwerk, J. and Hessner, S. and Lehmann, K. and Gökce, B. and Barcikowski, S.
    Journal of Laser Applications 28 (2016)
    We report on the substitution of silver nanoparticles' inks by silver microparticle dispersions as a material for the production of printable silver tracks by laser melting. This approach is promising, because it helps to reduce the production costs of such silver tracks. Though silver dispersions used as materials for laser melting mostly contain polyvinylpyrrolidone as a stabilizer, which results in the appearance of an undesired balling effect of silver during laser melting, the authors test stabilizers differing in molecular weight and functionality. The resulting differences in colloidal and physicochemical properties are investigated and related to the final silver layer quality. © 2016 Laser Institute of America.
    view abstractdoi: 10.2351/1.4955011
  • 2016 • 139 Silver-doped zinc oxide single nanowire multifunctional nanosensor with a significant enhancement in response
    Lupan, O. and Cretu, V. and Postica, V. and Ahmadi, M. and Cuenya, B.R. and Chow, L. and Tiginyanu, I. and Viana, B. and Pauporté, T. and Adelung, R.
    Sensors and Actuators, B: Chemical 223 893-903 (2016)
    Enhanced performances were obtained for nanosensors based on a single nanowire of silver-doped zinc oxide (ZnO:Ag). Arrays of crystalline ZnO:Ag nanowires were synthesized by electrodeposition on F-doped tin oxide coated substrates and studied by SEM, EDX, TEM, HRTEM, SIMS, XPS, PL and micro-Raman spectroscopy. Integration of a single nanowire or a single microwire on the chip was performed by employing metal maskless nanodeposition in the dual beam focused electron/ion beam instrument. The ultraviolet (UV) response and hydrogen (H2) gas response were studied for nanodevices and microdevices based on a single ZnO:Ag nanowire. We found that ZnO:Ag nanowire based nanosensor possesses a much faster response/recovery time and a higher response to UV radiation and hydrogen gas (∼50%) than those reported in literature. An increase in current value of about two orders in magnitude IUVON/IUVOFF was observed under exposure to UV light. Faster response/recovery times of about 0.98 s/0.87 s were observed. The ZnO:Ag nanowires and microwires can serve as nano-building materials for ultrasensitive and ultra-fast sensors with reduced power consumption. The mechanisms for such improved responses to UV and H2 were discussed. The developed nanomaterial is of great scientific interest for further studies as promising candidates for fabricating multifunctional nano-sensors, LEDs and photodetectors by bottom-up and hybrid nanotechnologies. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.snb.2015.10.002
  • 2016 • 138 Physisorption versus chemisorption of oxygen molecules on Ag(100)
    Mehlhorn, M. and Morgenstern, K.
    Journal of Chemical Physics 144 (2016)
    We compare the adsorption of oxygen molecules on Ag(100) at 60 K and at 100 K. At both temperatures, the molecules form islands. Differences between the species adsorbed at the two temperatures in both low-temperature scanning tunneling microscopy and inelastic electron tunneling spectroscopy are attributed to two different adsorption states, a chemisorbed state after 100 K adsorption and a physisorbed state after 60 K adsorption. © 2016 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4945339
  • 2016 • 137 Beam-induced atomic migration at Ag-containing nanofacets at an asymmetric Cu grain boundary
    Peter, N.J. and Liebscher, C.H. and Kirchlechner, C. and Dehm, G.
    Journal of Materials Research 32 968-982 (2016)
    Besides the high spatial resolution achieved in aberration-corrected scanning transmission microscopy, beam-induced dynamic effects have to be considered for quantitative chemical characterization on the level of single atomic columns. The present study investigates the influence of imaging conditions in an aberration-corrected scanning transmission electron microscope on the beam-induced atomic migration at a complex Ag-segregated, nanofaceted Cu grain boundary. Three distinct imaging conditions including static single image and serial image acquisition have been utilized. Chemical information on the Ag column occupation of single atomic columns at the grain boundary was extracted by the evolution of peak intensity ratios and compared to idealized scanning transmission electron microscopy image simulations. The atomic column occupation is underestimated when using conventional single frame acquisition due to an averaging of Ag atomic migration events during acquisition. Possible migration paths for the beam-induced atomic motion at a complex Cu grain boundary are presented. Copyright © Materials Research Society 2016
    view abstractdoi: 10.1557/jmr.2016.398
  • 2016 • 136 Modifying the Surface of a Rashba-Split Pb-Ag Alloy Using Tailored Metal-Organic Bonds
    Stadtmüller, B. and Seidel, J. and Haag, N. and Grad, L. and Tusche, C. and Van Straaten, G. and Franke, M. and Kirschner, J. and Kumpf, C. and Cinchetti, M. and Aeschlimann, M.
    117 (2016)
    Hybridization-related modifications of the first metal layer of a metal-organic interface are difficult to access experimentally and have been largely neglected so far. Here, we study the influence of specific chemical bonds (as formed by the organic molecules CuPc and PTCDA) on a Pb-Ag surface alloy. We find that delocalized van der Waals or weak chemical π-type bonds are not strong enough to alter the alloy, while localized σ-type bonds lead to a vertical displacement of the Pb surface atoms and to changes in the alloy's surface band structure. Our results provide an exciting platform for tuning the Rashba-type spin texture of surface alloys using organic molecules. © 2016 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.117.096805
  • 2015 • 135 Complex Surface Diffusion Mechanisms of Cobalt Phthalocyanine Molecules on Ag(100)
    Antczak, G. and Kamiński, W. and Sabik, A. and Zaum, C. and Morgenstern, K.
    Journal of the American Chemical Society 137 14920-14929 (2015)
    We used time-lapsed scanning tunneling microscopy between 43 and 50 K and density functional theory (DFT) to explore the basic surface diffusion steps of cobalt phthalocyanine (CoPc) molecules on the Ag(100) surface. We show that the CoPc molecules translate and rotate on the surface in the same temperature range. Both processes are associated with similar activation energies; however, the translation is more frequently observed. Our DFT calculations provide the activation energies for the translation of the CoPc molecule between the nearest hollow sites and the rotation at both the hollow and the bridge sites. The activation energies are only consistent with the experimental findings, if the surface diffusion mechanism involves a combined translational and rotational molecular motion. Additionally, two channels of motion are identified: the first provides only a channel for translation, while the second provides a channel for both the translation and the rotation. The existence of the two channels explains a higher rate for the translation determined in experiment. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/jacs.5b08001
  • 2015 • 134 Adsorption of a Switchable Industrial Dye on Au(111) and Ag(111)
    Boom, K. and Müller, M. and Stein, F. and Ernst, S. and Morgenstern, K.
    Journal of Physical Chemistry C 119 17718-17724 (2015)
    We investigate astraphloxine, an industrial dye, on two metal surfaces, Au(111) and Ag(111). Low-temperature scanning tunneling microscopy with submolecular resolution in comparison to semiempirical calculations reveal that only two of the nine possible conformers of this molecule are adsorbed. The two conformers adsorb via one of their indol groups, which serves as a platform that decouples the rest of the molecule from the surfaces. A change from one to the other conformer is demonstrated by injecting inelastic electrons from the tunneling tip selectively into individual molecules. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.jpcc.5b04883
  • 2015 • 133 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 • 132 The geometric and electronic structure of TCNQ and TCNQ+Mn on Ag(0 0 1) and Cu(0 0 1) surfaces
    Feyer, V. and Graus, M. and Nigge, P. and Zamborlini, G. and Acres, R.G. and Schöll, A. and Reinert, F. and Schneider, C.M.
    Journal of Electron Spectroscopy and Related Phenomena 204 125-131 (2015)
    Copper and silver surfaces can be used as model systems to study structure formation and interfacial bonding upon adsorption of organic molecules. We have investigated the geometric and electronic structure of ordered monolayers of TCNQ on Cu(0 0 1) and Ag(0 0 1) and of TCNQ+Mn on Ag(0 0 1) surfaces by LEED and photoelectron momentum microscopy. While TCNQ forms an incommensurable superstructure on Cu(0 0 1), two coverage-dependant, commensurable superstructures are established on Ag(0 0 1). Subsequent adsorption of Mn on top of TCNQ/Ag(0 0 1) results in the formation of a long-range ordered mixed metal-organic superstructure, which is also commensurable with the Ag(0 0 1) substrate. The photoelectron spectroscopy (PES) data shows a filling of the TCNQ LUMO by charge transfer from the substrate for all investigated interfaces and the coadsorption of Mn leads to an energy shift of the TCNQ HOMO and LUMO of 230 meV with respect to TCNQ/Ag(0 0 1). The characteristic angle-dependent intensity pattern of the TCNQ LUMO in PES was utilized to investigate the azimuthal orientation of the molecules in the respective unit cells. The angle-resolved PES data was further analyzed to identify lateral band dispersion effects in the adsorbate layers, but no significant dispersion was observed. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.elspec.2015.02.010
  • 2015 • 131 Diffusion limited aggregation in low temperature growth of sodium chloride
    Gerß, B. and Osterloh, N. and Heidorn, S.-C. and Morgenstern, K.
    Crystal Growth and Design 15 3046-3051 (2015)
    Sodium chloride is adsorbed at low temperature on Cu(111) and investigated by scanning tunneling microscopy. The ramified shape of the lowerature grown islands and early second layer nucleation suggest diffusion-limited aggregation of crystallites as corroborated by atomically resolved images of the highly disordered salt clusters. A comparison to single crystalline islands grown at room temperature on Ag(111) reveals differences in bond length and angle and thus crystal order for the lowerature phase. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.cgd.5b00486
  • 2015 • 130 Ripening kinetics of laser-generated plasmonic nanoparticles in different solvents
    Gökce, B. and Van't Zand, D.D. and Menéndez-Manjón, A. and Barcikowski, S.
    Chemical Physics Letters 626 96-101 (2015)
    Abstract Pulsed laser ablation in liquid is considered to be a fast nanoparticle-synthesis method taking place on ps to μs timescale. Here, we report the comparably slow ripening kinetics of laser-generated plasmonic nanoparticles (copper, silver, and gold) immediately after ablation. The growth dynamics is studied in situ by following the surface plasmon resonance and correlated to known models. We thereby identify a two-step diffusion-controlled coalescence and growth mechanism, quantify their kinetic constants and show the effect of different solvents (water, acetone, ethanol, and ethyl acetate). © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.cplett.2015.03.010
  • 2015 • 129 Quantitative replacement of citrate by phosphane on silver nanoparticle surfaces monitored by Surface-Enhanced Raman Spectroscopy (SERS)
    Grass, S. and Diendorf, J. and Gebauer, J.S. and Epple, M. and Treuel, L.
    Journal of Nanoscience and Nanotechnology 15 1591-1596 (2015)
    Chemical approaches to metal NP synthesis commonly use capping agents to achieve a desired NP size and shape. Frequently, such NPs require chemically different surface ligands after synthesis to generate desired NP properties (e.g., charge or hydrophilicity) and to increase their long term colloidal stability. Here, we prepared SERS active citrate-stabilized silver NPs (d = 38 ± 4 nm), purified them from remaining reactants by ultracentrifugation and redispersion, and immersed them into solutions containing different concentrations of Tris(sodium-m-sulfonatophenyl)phosphine (TPPTS), which is often used in such ligand replacement approaches to increase colloidal stability. After equilibration, SERS spectra were acquired, elucidating the concentration dependence of the ligand replacement reaction. SERS data were complemented by concentration dependent size measurements and relations between ligand exchange and colloidal stability are discussed. Copyright © 2015 American Scientific Publishers
    view abstractdoi: 10.1166/jnn.2015.9143
  • 2015 • 128 The effect of patterned titanium substrates on the properties of silver-doped hydroxyapatite coatings
    Grubova, I.Y. and Surmeneva, M.A. and Ivanova, A.A. and Kravchuk, K. and Prymak, O. and Epple, M. and Buck, V. and Surmenev, R.A.
    Surface and Coatings Technology 276 595-601 (2015)
    This paper reports the effect of substrate nano/micro-structure design on the grain size, mechanical properties and surface wettability of nanostructured radio frequency (RF) magnetron sputter-deposited silver-containing hydroxyapatite (Ag-HA) coatings containing 0.13-0.36. wt.% silver. The results of this study revealed that the Ag-HA coating microstructure could be designed by controlling the pre-treated surface topography of titanium. The nano/micro-patterned surfaces of titanium were prepared by sand-blasting followed by acid-etching. The size of the nano-patterns on the surface of titanium was also affected by the sand-blasting procedure; namely, the lower the pressure was, the larger the size of the nano-structures and the distance between them. The effect of the coating grain size on the surface wettability and physico-mechanical properties of the biocomposites was revealed. The hydrophobic properties were imparted to the rough titanium by a nanostructured Ag-HA coating. Although according to the XRD patterns the coatings were mainly composed of HA, some differences in the morphology were observed. Therefore, the decreased wettability of the Ag-HA coatings could be explained by taking into account the different grain sizes of the films rather than the changes to the surface chemistry. Nanoindentation studies revealed that in the case of the Ag-HA-coated samples, smaller grains resulted in significantly higher nanohardness and Young's modulus. © 2015 Elsevier B.V..
    view abstractdoi: 10.1016/j.surfcoat.2015.06.010
  • 2015 • 127 Surface plasmon coupled chemiluminescence during adsorption of oxygen on magnesium surfaces
    Hagemann, U. and Nienhaus, H.
    Journal of Chemical Physics 143 (2015)
    The dissociative adsorption of oxygen molecules on magnesium surfaces represents a non-adiabatic reaction exhibiting exoelectron emission, chemicurrent generation, and weak chemiluminescence. Using thin film Mg/Ag/p-Si(111) Schottky diodes with 1 nm Mg on a 10-60 nm thick Ag layer as 2π-photodetectors, the chemiluminescence is internally detected with a much larger efficiency than external methods. The chemically induced photoyield shows a maximum for a Ag film thickness of 45 nm. The enhancement is explained by surface plasmon coupled chemiluminescence, i.e., surface plasmon polaritons are effectively excited in the Ag layer by the oxidation reaction and decay radiatively leading to the observed photocurrent. Model calculations of the maximum absorption in attenuated total reflection geometry support the interpretation. The study demonstrates the extreme sensitivity and the practical usage of internal detection schemes for investigating surface chemiluminescence. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4938996
  • 2015 • 126 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 • 125 Influence of water on supra-molecular assembly of 4, 4′-dihydroxy azobenzene on Ag(111)
    Henzl, J. and Boom, K. and Morgenstern, K.
    Journal of Chemical Physics 142 (2015)
    We explore co-deposition of water and 4, 4′-dihydroxy azobenzene on Ag(111) by low-temperature scanning tunneling microscopy at different water-to-azobenzene ratios. At all ratios, the water interacts with the hydroxyl end groups of the molecule replacing the direct hydrogen bonding. The change in bonding reduces the azobenzene density as compared to the one in the closed-packed waterless azobenzene structure. At intermediate water-to-azobenzene ratios, pores are formed in the azobenzene layer at nanometer distance from the water. At high water-to-azobenzene ratios, a water superstructure with a 1.4 nm × 1.4 nm unit cell develops. Our results point to a method to vary the density of an organic layer by tuning the amount of an inorganic additive. © 2015 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4907368
  • 2015 • 124 Hybrid biocomposite with a tunable antibacterial activity and bioactivity based on RF magnetron sputter deposited coating and silver nanoparticles
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Loza, K. and Prymak, O. and Epple, M.
    Applied Surface Science 329 212-218 (2015)
    In this work, we describe fabrication techniques used to prepare a multifunctional biocomposite based on a hydroxyapatite (HA) coating and silver nanoparticles (AgNPs). AgNPs synthesized by a wet chemical reduction method were deposited on Ti substrates using a dripping/drying method followed by deposition of calcium phosphate (CaP) coating via radio-frequency (RF) magnetron sputter-deposition. The negatively charged silver nanoparticles (zeta potential -21 mV) have a spherical shape with a metallic core diameter of 50 ± 20 nm. The HA coating was deposited as a dense nanocrystalline film over a surface of AgNPs. The RF-magnetron sputter deposition of HA films on the AgNPs layer did not affect the initial content of AgNPs on the substrate surface as well as NPs size and shape. SEM cross-sectional images taken using the backscattering mode revealed a homogeneous layer of AgNPs under the CaP layer. The diffraction patterns from the coatings revealed reflexes of crystalline HA and silver. The concentration of Ag ions released from the biocomposites after 7 days of immersion in phosphate and acetate buffers was estimated. The obtained results revealed that the amount of silver in the solutions was 0.27 ± 0.02 μg mL-1 and 0.54 ± 0.02 μg mL-1 for the phosphate and acetate buffers, respectively, which corresponded well with the minimum inhibitory concentration range known for silver ions in literature. Thus, this work establishes a new route to prepare a biocompatible layer using embedded AgNPs to achieve a local antibacterial effect. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2014.12.153
  • 2015 • 123 Antibacterial activity of microstructured Ag/Au sacrificial anode thin films
    Köller, M. and Sengstock, C. and Motemani, Y. and Khare, C. and Buenconsejo, P.J.S. and Geukes, J. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 46 276-280 (2015)
    Ten different Ag dot arrays (16 to 625 microstructured dots per square mm) were fabricated on a continuous Au thin film and for comparison also on Ti film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Escherichia coli and Staphylococcus aureus were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards both bacterial strains was induced by Ag dot arrays on fabricated Au thin film (sacrificial anode system for Ag), due to the release of Ag ions from dissolution of Ag dots in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag) which remained intact to the original dot shape. The required number of Ag dots on gold film to achieve complete bactericidal effects for both bacterial strains was seven times lower than that observed with Ag dot arrays on Ti film. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.msec.2014.10.058
  • 2015 • 122 The fate of nano-silver in aqueous media
    Plowman, B.J. and Tschulik, K. and Walport, E. and Young, N.P. and Compton, R.G.
    Nanoscale 7 12361-12364 (2015)
    Silver nanoparticles offer highly attractive properties for many applications, however concern has been raised over the possible toxicity of this material in environmental systems. While it is thought that the release of Ag+ can play a crucial role in this toxicity, the mechanism by which the oxidative dissolution of nano-silver occurs is not yet understood. Here we address this through the electrochemical analysis of gold-core silver-shell nanoparticles in various solutions. This novel method allows the direct quantification of silver dissolution by normalisation to the gold core signal. This is shown to be highly effective at discriminating between silver dissolution and the loss of nanoparticles from the electrode surface. We evidence through this rigorous approach that the reduction of O<inf>2</inf> drives the dissolution of nano-silver, while in the presence of Cl- this dissolution is greatly inhibited. This work is extended to the single nanoparticle level using nano-impact experiments. © The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c5nr02995c
  • 2015 • 121 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 • 120 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 • 119 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 • 118 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 • 117 Reversible or Not? Distinguishing Agglomeration and Aggregation at the Nanoscale
    Sokolov, S.V. and Tschulik, K. and Batchelor-McAuley, C. and Jurkschat, K. and Compton, R.G.
    Analytical Chemistry 87 10033-10039 (2015)
    Nanoparticles are prone to clustering either via aggregation (irreversible) or agglomeration (reversible) processes. It is exceedingly difficult to distinguish the two via conventional techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), or electron microscopy imaging (scanning electron microscopy (SEM), transmission electron microscopy (TEM)) as such techniques only generally confirm the presence of large particle clusters. Herein we develop a joint approach to tackle the issue of distinguishing between nanoparticle aggregation vs agglomeration by characterizing a colloidal system of Ag NPs using DLS, NTA, SEM imaging and the electrochemical nanoimpacts technique. In contrast to the conventional techniques which all reveal the presence of large clusters of particles, electrochemical nanoimpacts provide information regarding individual nanoparticles in the solution phase and reveal the presence of small nanoparticles (<30 nm) even in high ionic strength (above 0.5 M KCl) and allow a more complete analysis. The detection of small nanoparticles in high ionic strength media evidence the clustering to be a reversible process. As a result it is concluded that agglomeration rather than irreversible aggregation takes place. This observation is of general importance for all colloids as it provides a feasible analysis technique for a wide range of systems with an ability to distinguish subtly different processes. © 2015 American Chemical Society.
    view abstractdoi: 10.1021/acs.analchem.5b02639
  • 2015 • 116 Are Nanoparticles Spherical or Quasi-Spherical?
    Sokolov, S.V. and Batchelor-Mcauley, C. and Tschulik, K. and Fletcher, S. and Compton, R.G.
    Chemistry - A European Journal 21 10741-10746 (2015)
    The geometry of quasi-spherical nanoparticles is investigated. The combination of SEM imaging and electrochemical nano-impact experiments is demonstrated to allow sizing and characterization of the geometry of single silver nanoparticles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/chem.201500807
  • 2015 • 115 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 • 114 Influence of gold, silver and gold-silver alloy nanoparticles on germ cell function and embryo development
    Taylor, U. and Tiedemann, D. and Rehbock, C. and Kues, W.A. and Barcikowski, S. and Rath, D.
    Beilstein Journal of Nanotechnology 6 651-664 (2015)
    The use of engineered nanoparticles has risen exponentially over the last decade. Applications are manifold and include utilisation in industrial goods as well as medical and consumer products. Gold and silver nanoparticles play an important role in the current increase of nanoparticle usage. However, our understanding concerning possible side effects of this increased exposure to particles, which are frequently in the same size regime as medium sized biomolecules and accessorily possess highly active surfaces, is still incomplete. That particularly applies to reproductive aspects, were defects can be passed onto following generations. This review gives a brief overview of the most recent findings concerning reprotoxicological effects. The here presented data elucidate how composition, size and surface modification of nanoparticles influence viablility and functionality of reproduction relevant cells derived from various animal models. While in vitro cultured embryos displayed no toxic effects after the microinjection of gold and silver nanoparticles, sperm fertility parameters deteriorated after co-incubation with ligand free gold nanoparticles. However, the effect could be alleviated by bio-coating the nanoparticles, which even applies to silver and silver-rich alloy nanoparticles. The most sensitive test system appeared to be in vitro oocyte maturation showing a dose-dependent response towards protein (BSA) coated gold-silver alloy and silver nanoparticles leading up to complete arrest of maturation. Recent biodistribution studies confirmed that nanoparticles gain access to the ovaries and also penetrate the blood-testis and placental barrier. Thus, the design of nanoparticles with increased biosafety is highly relevant for biomedical applications. © 2015 Taylor et al.
    view abstractdoi: 10.3762/bjnano.6.66
  • 2015 • 113 Hot electron-induced reduction of small molecules on photorecycling metal surfaces
    Xie, W. and Schlücker, S.
    Nature Communications 6 (2015)
    Noble metals are important photocatalysts due to their ability to convert light into chemical energy. Hot electrons, generated via the non-radiative decay of localized surface plasmons, can be transferred to reactants on the metal surface. Unfortunately, the number of hot electrons per molecule is limited due to charge-carrier recombination. In addition to the reduction half-reaction with hot electrons, also the corresponding oxidation counter-half-reaction must take place since otherwise the overall redox reaction cannot proceed. Here we report on the conceptual importance of promoting the oxidation counter-half-reaction in plasmon-mediated catalysis by photorecycling in order to overcome this general limitation. A six-electron photocatalytic reaction occurs even in the absence of conventional chemical reducing agents due to the photoinduced recycling of Ag atoms from hot holes in the oxidation half-reaction. This concept of multi-electron, counter-half-reaction-promoted photocatalysis provides exciting new opportunities for driving efficient light-to-energy conversion processes. © 2015 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/ncomms8570
  • 2014 • 112 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 • 111 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 • 110 Stabilizing CuPc coordination networks on Ag(100) by Ag atoms
    Antczak, G. and Kamiński, W. and Morgenstern, K.
    Journal of Physical Chemistry C 119 1442-1450 (2014)
    We demonstrate that Ag adatoms are capable of stabilizing negatively charged copper-phthalocyanine (CuPc) molecules in a Ag-CuPc network at room temperature. For this aim, the structure of the Ag-CuPc coordination network at different molecule-adatom densities is investigated experimentally by scanning tunneling microscopy and theoretically by firstprinciples calculations. The islands formed at saturation adatom density, close to the source of adatoms, consist of a closed-packed layer without voids. The islands formed at lower adatom density consist of an irregular arrangement of larger entities, named subunits, mainly (CuPc)4Ag and (CuPc)6Ag2, which are interconnected in the same fashion as the CuPc molecules in the closed-packed layer. Silver adatoms in the subunits and between them differ by the number of molecules they link. The Ag-CuPc networks are stabilized, because the adsorption energy of CuPc molecules increases due to the presence of adatoms. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/jp5103803
  • 2014 • 109 Fabrication of Ag/TiO2 photocatalyst for the treatment of simulated hospital wastewater under sunlight
    Badawy, M.I. and Souaya, E.M.R. and Gad-Allah, T.A. and Abdel-Wahed, M.S. and Ulbricht, M.
    Environmental Progress and Sustainable Energy 33 886-894 (2014)
    In this study, photocatalytic activity of titanium dioxide was modified by doping with silver metal. This was done by simple preparation procedure at room temperature. Different preparation conditions were studied and their effects on photocatalytic activity were investigated. The obtained nanopowders were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area measurement, UV-Visible absorption, and transmission electron microscope (TEM). Photocatalytic activities of the prepared samples under simulated sunlight were evaluated with respect to their efficiencies for the degradation of five pharmaceutical compounds commonly present in hospital wastewater. Prepared samples showed very high efficiency for photodegradation of the studied pharmaceutical compounds. Maximum photodegradation rate of the simulated hospital wastewater was obtained using 1000 ppm of the material with 0.1% Ag/TiO2 (weight ratio) calcined at 300°C and pH 5. However, the best pH of the degradation of each pharmaceutical compound varies according to the pKa. © 2013 American Institute of Chemical Engineers.
    view abstractdoi: 10.1002/ep.11869
  • 2014 • 108 Structural evolution of silver nanoparticles during wet-chemical synthesis
    Banerjee, S. and Loza, K. and Meyer-Zaika, W. and Prymak, O. and Epple, M.
    Chemistry of Materials 26 951-957 (2014)
    The formation of silver nanoparticles during the reduction with glucose in the presence of poly(N-vinyl pyrrolidone) as capping agent was followed for more than 3000 min. First, spherical silver nanoparticles are formed, but in later stages, an increasing fraction of nanotriangles and also a few nanorods develop. Both spherical and trigonal nanoparticles grow with time, indicating separate nucleation pathways. The domain size in the spherical nanoparticles increases proportionally to the particle diameter and is always about 1/ 4 of the diameter, indicating that twinned seeds are formed very early in the process and then simply grow by extending their domains. The lattice constant of the nanoparticles is systematically increased in comparison to microcrystalline silver (4.0877 vs 4.08635 Å) but did not change as a function of particle diameter. A thorough analysis of the texture coefficient, supported by transmission electron microscopy data, showed that the apparently spherical particles are in fact flattened pentagonal prisms, which typically lie on their flat pentagonal face. Neither the presence of oxygen nor the presence of ambient light had any influence on the particle properties. © 2014 American Chemical Society.
    view abstractdoi: 10.1021/cm4025342
  • 2014 • 107 Simultaneous electrochemical and 3D optical imaging of silver nanoparticle oxidation
    Batchelor-Mcauley, C. and Martinez-Marrades, A. and Tschulik, K. and Patel, A.N. and Combellas, C. and Kanoufi, F. and Tessier, G. and Compton, R.G.
    Chemical Physics Letters 597 20-25 (2014)
    The oxidation of AgNPs at a thin-film gold electrode is simultaneously investigated via digital holography and electrochemistry. The use of holography allows, for the first time, the 3D visualization of the electrochemical interfacial region at a relatively high acquisition rate. It is demonstrated how the coupling of these two techniques provides complementary chemical information. The ensemble response of the oxidation of surface-adsorbed silver nanoparticles to AgCl is monitored electrochemically, whereas this process is difficult to observe optically. Conversely, the subsequent chemical dissolution of individual AgCl nanocrystals can be tracked optically due to the associated decrease in the scattered light intensity. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.cplett.2014.02.007
  • 2014 • 106 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 • 105 Spectroelectrochemical and morphological studies of the ageing of silver nanoparticles embedded in ultra-thin perfluorinated sputter deposited films
    Ebbert, C. and Alissawi, N. and Somsen, C. and Eggeler, G. and Strunskus, T. and Faupel, F. and Grundmeier, G.
    Thin Solid Films 571 161-167 (2014)
    This paper focuses on the investigation of the ageing behaviour of silver nanoparticle containing polytetrafluoroethylene thin films during exposure to phosphate buffer solution (pH = 7.5). In order to investigate the effect of the electrical connection between the silver nanoparticles via a conductive substrate, two kinds of composite films were compared. One model where the nanoparticles are directly deposited on an inert conducting substrate and then covered by an ultra-thin polytetrafluoroethylene like film. In the second case a polytetrafluoroethylene/silver nanoparticle/polytetrafluoroethylene sandwich film was prepared on the same substrate to prevent electrical connection of the silver nanoparticles. Degradation was followed in-situ by means of the combination of ultraviolet-visible spectroscopy and electrochemical impedance spectroscopy. In the case of electrically connected nanoparticles electrochemical Ostwald ripening took place, while this process was not observed for the insulated nanoparticles. The electrochemical impedance spectroscopy studies allowed for the parallel study of the correlated loss of barrier properties. Transmission electron microscopy images of both composite films confirmed the results obtained by means of the in situ electrochemical ultraviolet-visible studies. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2014.10.054
  • 2014 • 104 The use of cylindrical micro-wire electrodes for nano-impact experiments; Facilitating the sub-picomolar detection of single nanoparticles
    Ellison, J. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    Sensors and Actuators, B: Chemical 200 47-52 (2014)
    Electrochemical impact experiments can be used to detect and size single nanoparticles in suspension and at low concentrations. This is generally performed using a micro-disc working electrode; however, for the first time we report the use of cylindrical micro-wire electrodes for nanoparticle impact experiments. These electrodes provide much enhanced detection limits; specifically decreasing the concentration of nanoparticles measurable by over two orders of magnitude. In addition, the use of micro-wire electrodes reduces the shielding effect due to absorption of particles to the insulating sheath that surrounds a micro-disc electrode. Micro-wire electrodes are fabricated and their electrochemical response analysed via cyclic voltammetry experiments using molecular species. This provides a theoretical framework which is used to calculate the reduced concentration of nanoparticles required for an impact experiment at a micro-cylinder electrode in comparison to the micro-disc. Experimentally, it is demonstrated that impact experiments on the micro-cylinder electrodes can indeed be used for accurate characterisation of ultra-low concentrations (≈0.1 pM) of silver nanoparticles. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.snb.2014.03.085
  • 2014 • 103 Adsorption geometry and electronic structure of iron phthalocyanine on Ag surfaces: A LEED and photoelectron momentum mapping study
    Feyer, V. and Graus, M. and Nigge, P. and Wießner, M. and Acres, R.G. and Wiemann, C. and Schneider, C.M. and Schöll, A. and Reinert, F.
    Surface Science 621 64-68 (2014)
    We present a comprehensive study of the adsorption behavior of iron phthalocyanine on the low-index crystal faces of silver. By combining measurements of the reciprocal space by means of photoelectron momentum mapping and low energy electron diffraction, the real space adsorption geometries are reconstructed. At monolayer coverage ordered superstructures exist on all studied surfaces containing one molecule in the unit cell in case of Ag(100) and Ag(111), and two molecules per unit cell for Ag(110). The azimuthal tilt angle of the molecules against the high symmetry directions of the substrate is derived from the photoelectron momentum maps. A comparative analysis of the momentum patterns on the substrates with different symmetry indicates that both constituents of the twofold degenerate FePc lowest unoccupied molecular orbital are occupied by charge transfer from the substrate at the interface. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.susc.2013.10.020
  • 2014 • 102 Comparison of different characterization methods for nanoparticle dispersions before and after aerosolization
    Fissan, H. and Ristig, S. and Kaminski, H. and Asbach, C. and Epple, M.
    Analytical Methods 6 7324-7334 (2014)
    A well-known and accepted aerosol measurement technique, the scanning mobility particle sizer (SMPS), is applied to characterize colloidally dispersed nanoparticles. To achieve a transfer from dispersed particles to aerosolized particles, a newly developed nebulizer (N) is used that, unlike commonly used atomizers, produces significantly smaller droplets and therefore reduces the problem of the formation of residual particles. The capabilities of this new instrument combination (N + SMPS) for the analysis of dispersions were investigated, using three different dispersions, i.e. gold-PVP nanoparticles (∼20 nm), silver-PVP nanoparticles (∼70 nm) and their 1:1 (m:m) mixture. The results are compared to scanning electron microscopy (SEM) measurements and two frequently applied techniques for characterizing colloidal systems: Dynamic light scattering (DLS) and analytical disc centrifugation (ADC). The differences, advantages and disadvantages of each method are discussed, especially with respect to the size resolution of the techniques and their ability to distinguish the particle sizes of the mixed dispersion. While DLS is, as expected, unable to resolve the binary dispersion, SEM, ADC and SMPS are able to give quantitative information on the two particle sizes. However, while the high-resolving ADC is limited due to the dependency on a predefined density of the investigated system, the transfer of dispersed particles into an aerosol and subsequent analysis with SMPS are an adequate way to characterize binary systems, independent of the density of concerned particles, but matching the high resolution of the ADC. We show that it is possible to use the well-established aerosol measurement technique (N + SMPS) in colloid science with all its advantages concerning size resolution and accuracy. © the Partner Organisations 2014.
    view abstractdoi: 10.1039/c4ay01203h
  • 2014 • 101 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 • 100 Atom probe tomography observation of hydrogen in high-Mn steel and silver charged via an electrolytic route
    Haley, D. and Merzlikin, S.V. and Choi, P. and Raabe, D.
    International Journal of Hydrogen Energy 39 12221-12229 (2014)
    We investigate an electrolytic route for hydrogen charging of metals and its detection in Atom Probe Tomography (APT) experiments. We charge an austenitic Fe-30Mn-8Al-1.2C (wt.%) weight reduced high-Mn steel and subsequently demonstrate the detectability of deuterium in an APT experiment. The experiment is repeated with a deposited Ag film upon an APT tip of a high-Mn steel. It is shown that a detectable deuterium signal can be seen in the high-Mn steel, and a D:H ratio of 0.84 can be reached in Ag films. Additionally, it was found that the predicted time constraint on detectability of D in APT was found to be lower than predicted by bulk diffusion for the high-Mn steel. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijhydene.2014.05.169
  • 2014 • 99 Size dependence of the dispersion relation for the interface state between NaCl(100) and Ag(111)
    Heidorn, S.-C. and Sabellek, A. and Morgenstern, K.
    Nano Letters 14 13-17 (2014)
    This study investigates the interface state electron dispersion relation between NaCl(100) islands and Ag(111) dependent upon NaCl island size. Both onset energy and effective mass are size dependent. However, these dependencies are relevant at different island sizes. We trace back this effective mass dependency to a misfit-induced strain based on atomically resolved images. Our results open up new avenues for the development of nanodevices by tuning the effective electron mass via strain of the insulating component. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/nl403121t
  • 2014 • 98 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 • 97 Proinflammatory and cytotoxic response to nanoparticles in precision-cut lung slices
    Hirn, S. and Haberl, N. and Loza, K. and Epple, M. and Kreyling, W.G. and Rothen-Rutishauser, B. and Rehberg, M. and Krombach, F.
    Beilstein Journal of Nanotechnology 5 2440-2449 (2014)
    Precision-cut lung slices (PCLS) are an established ex vivo alternative to in vivo experiments in pharmacotoxicology. The aim of this study was to evaluate the potential of PCLS as a tool in nanotoxicology studies. Silver (Ag-NPs) and zinc oxide (ZnO-NPs) nanoparticles as well as quartz particles were used because these materials have been previously shown in several in vitro and in vivo studies to induce a dose-dependent cytotoxic and inflammatory response. PCLS were exposed to three concentrations of 70 nm monodisperse polyvinylpyrrolidone (PVP)-coated Ag-NPs under submerged culture conditions in vitro. ZnO-NPs (NM110) served as 'soluble' and quartz particles (Min-U-Sil) as 'non-soluble' control particles. After 4 and 24 h, the cell viability and the release of proinflammatory cytokines was measured. In addition, multiphoton microscopy was employed to assess the localization of Ag-NPs in PCLS after 24 h of incubation. Exposure of PCLS to ZnO-NPs for 4 and 24 h resulted in a strong decrease in cell viability, while quartz particles had no cytotoxic effect. Moreover, only a slight cytotoxic response was detected by LDH release after incubation of PCLS with 20 or 30 μg/mL of Ag-NPs. Interestingly, none of the particles tested induced a proinflammatory response in PCLS. Finally, multiphoton microscopy revealed that the Ag-NP were predominantly localized at the cut surface and only to a much lower extent in the deeper layers of the PCLS. In summary, only 'soluble' ZnO-NPs elicited a strong cytotoxic response. Therefore, we suggest that the cytotoxic response in PCLS was caused by released Zn2+ ions rather than by the ZnO-NPs themselves. Moreover, Ag-NPs were predominantly localized at the cut surface of PCLS but not in deeper regions, indicating that the majority of the particles did not have the chance to interact with all cells present in the tissue slice. In conclusion, our findings suggest that PCLS may have some limitations when used for nanotoxicology studies. To strengthen this conclusion, however, other NP types and concentrations need to be tested in further studies. © 2014 Hirn et al.
    view abstractdoi: 10.3762/bjnano.5.253
  • 2014 • 96 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 • 95 Antibacterial AgNPs/CaP biocomposites
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Sharonova, A.A. and Grubova, I.Y. and Loza, K. and Chernousova, S. and Prymak, O. and Epple, M.
    2014 9th International Forum on Strategic Technology, IFOST 2014 472-474 (2014)
    The modification of implant surface is in the focus of many scientists worldwide. In this study, multifunctional biocomposite on the basis of calcium phosphate coating and silver nanoparticles has been fabricated through the use of nanofabrication techniques. Dense nanocrystalline HA film was deposited over AgNPs. The properties as well as the in vitro behavior of the developed biocomposites have been studied. The diffraction patterns of the biocomposites revealed the peaks of crystalline HA and silver (Ag). The release of Ag from the developed biocomposites was evaluated. The concentration of the released silver ions for 7 days of dissolution was 0.27±0.02 μg/mL and 0.54±0.02 μg/mL for phosphate and acetate buffers, respectively. In order to estimate the cytotoxicity of the samples the functional activity of osteoclasts, in particular, cell morphology, multinuclearity, actin ring and resorption pit on the substrates coated with HA and AgNPs-HA have been evaluated. © 2014 IEEE.
    view abstractdoi: 10.1109/IFOST.2014.6991166
  • 2014 • 94 Texture and microstructure evolution during non-crystallographic shear banding in a plane strain compressed Cu-Ag metal matrix composite
    Jia, N. and Raabe, D. and Zhao, X.
    Acta Materialia 76 238-251 (2014)
    We studied the texture and microstructure evolution in a plane strain compressed Cu-Ag metal matrix composite (MMC) with a heterophase microstructure using crystal plasticity finite element simulations. Lattice reorientations induced by both crystallographic (dislocation slip and twinning) and non-crystallographic (shear banding) mechanisms are addressed. First, simulations on a polycrystalline composite are made. Quite similar texture trends are observed for the composites and for the individual single-phase materials, namely, copper-type texture components in the Cu phase and brass-type texture components in the Ag phase. This result differs from experimental data that show less copper-type and more brass-type textures in both phases for the composite materials. To explore co-deformation mechanisms that lead to the specific crystallographic textures in the MMC, bicrystal simulations for the composite with specific initial orientation combinations are performed. The bicrystal simulations reproduce the experimentally observed trends of texture evolution in the respective phases of the composite, indicating that the localized stress and strain fields as well as the co-deformation mechanisms within the actual heterophase microstructure are well captured. The modeling shows that to accommodate plastic deformation between adjacent phases in the bicrystals, pronounced shear bands are triggered by stress concentration at the hetero-interfaces. With further deformation the bands penetrate through the phase boundaries and lead to larger lattice rotations. The simulations confirm that the shear banding behavior in heterophase composites is different from that in single-phase metals and the texture evolution in composite materials is strongly influenced by the starting texture, the local constraints exerted from the phase boundaries and the constitutive properties of the abutting phases. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2014.05.036
  • 2014 • 93 Anisotropy of electromigration-induced void and island drift
    Latz, A. and Sindermann, S.P. and Brendel, L. and Dumpich, G. and Meyer zu Heringdorf, F.-J. and Wolf, D.E.
    Journal of Physics Condensed Matter 26 (2014)
    By means of our novel self-learning kinetic Monte Carlo model (Latz et al 2012 J. Phys.: Condens. Matter 24 485005) we study the electromigration-induced drift of monolayer voids and islands on unpassivated surfaces of single crystalline Ag(111) and Ag(001) films at the atomic scale. Regarding the drift velocity, we find a non-monotonic size dependence for small voids. The drift direction is aligned with the electromigration force only along high symmetry directions, while halfway between, the angle enclosed by them is maximal. The magnitude of these directional deviations strongly depends on the system parameter, which are investigated in detail. The simulation results are in accordance with void motion observed in experiments performed on Ag(111). © 2014 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/26/5/055005
  • 2014 • 92 The predominant species of ionic silver in biological media is colloidally dispersed nanoparticulate silver chloride
    Loza, K. and Sengstock, C. and Chernousova, S. and Köller, M. and Epple, M.
    RSC Advances 4 35290-35297 (2014)
    We have investigated the behaviour of silver ions in biologically relevant concentrations (10 to 100 ppm) in different media, from physiological salt solution over phosphate-buffered saline solution to protein-containing cell culture media. The results show that the initially present silver ions are bound as silver chloride due to the presence of chloride. Only in the absence of chloride, glucose is able to reduce Ag+ to Ag0. The precipitation of silver phosphate was not observed in any case. We conclude that the predominant silver species in biological media is dispersed nanoscopic silver chloride, surrounded by a protein corona which prevents the growth of the crystals and leads to colloidal stabilization. Therefore, in cell culture experiments where dissolved silver ions are studied in the upper ppm range, in fact the effect of colloidally dispersed silver chloride is observed. We have confirmed this by cell culture experiments (human mesenchymal stem cells; T-cells; monocytes) and bacteria (S. aureus) where the cells were incubated with synthetically prepared silver chloride nanoparticles (diameter ca. 100 nm). These were easily taken up by eukaryotic cells and showed the same toxic effect at the same silver concentration as ionic silver (as silver acetate). Therefore, nanoscopic silver chloride and not free ionic silver is the primary toxic species in biological media. © 2014 the Partner Organisations.
    view abstractdoi: 10.1039/c4ra04764h
  • 2014 • 91 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 • 90 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 • 89 Lattice degradation by moving voids during reversible electromigration
    Sindermann, S.P. and Latz, A. and Spoddig, D. and Schoeppner, C. and Wolf, D.E. and Dumpich, G. and Meyer zu Heringdorf, F.-J.
    Journal of Applied Physics 116 (2014)
    Electromigration driven void motion is studied in Ag wires with an initially well-defined single crystal lattice by in situ scanning electron microscopy. Voids are moving in opposite direction to the electron flow. When the electron current is reversed, voids exactly retrace their previous motion path with an increased drift velocity: The microstructure of the Ag wire "remembers" the motion path of the initial voids. To investigate the nature of this memory effect, we analyzed the crystal lattice with electron backscatter diffraction after passing of a void. The results show a permanent lattice degradation caused by the moving void. The implication of this finding for the reversibility of EM will be discussed. © 2014 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4889816
  • 2014 • 88 Raman spectroscopy study of silicon nanoribbons on Ag(110)
    Speiser, E. and Buick, B. and Esser, N. and Richter, W. and Colonna, S. and Cricenti, A. and Ronci, F.
    Applied Physics Letters 104 (2014)
    The grating of self-assembled Si nanoribbons at the Ag(110) surface has been studied by Raman spectroscopy. The study, conducted in situ with uncapped samples, resulted in phonon frequencies in disagreement with the results of theoretical calculations reported in literature for freestanding silicene sheets and nanoribbons. These results suggest that the structure of these silicon nanoribbons is very different from the planar and lightly buckled structural models and that the influence of the substrate might be underestimated in the discussed structural models. © 2014 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4872460
  • 2014 • 87 Gold electrodes from recordable CDs for the sensitive, semi-quantitative detection of commercial silver nanoparticles in seawater media
    Stuart, E.J.E. and Tschulik, K. and Lowinsohn, D. and Cullen, J.T. and Compton, R.G.
    Sensors and Actuators, B: Chemical 195 223-229 (2014)
    We report the use of homemade disposable gold electrodes fabricated from commercial recordable CDs for the detection and quantification of silver nanoparticles from a consumer product in a seawater sample. The "CDtrode" is immersed in a seawater sample containing silver nanoparticles for a certain amount of time during which the silver nanoparticles adsorb onto the CDtrode surface under open circuit conditions. The CDtrode is then transferred to an aqueous electrolyte and oxidative stripping is used to determine the amount of silver nanoparticles that have become stuck to the electrode surface. Depending on immersion time and silver nanoparticle concentration, up to a full monolayer coverage of silver nanoparticles on the CDtrode surface has been achieved. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.snb.2014.01.040
  • 2014 • 86 Injection of ligand-free gold and silver nanoparticles into murine embryos does not impact pre-implantation development
    Taylor, U. and Garrels, W. and Barchanski, A. and Peterson, S. and Sajti, L. and Lucas-Hahn, A. and Gamrad, L. and Baulain, U. and Klein, S. and Kues, W.A. and Barcikowski, S. and Rath, D.
    Beilstein Journal of Nanotechnology 5 677-688 (2014)
    Intended exposure to gold and silver nanoparticles has increased exponentially over the last decade and will continue to rise due to their use in biomedical applications. In particular, reprotoxicological aspects of these particles still need to be addressed so that the potential impacts of this development on human health can be reliably estimated. Therefore, in this study the toxicity of gold and silver nanoparticles on mammalian preimplantation development was assessed by injecting nanoparticles into one blastomere of murine 2 cell-embryos, while the sister blastomere served as an internal control. After treatment, embryos were cultured and embryo development up to the blastocyst stage was assessed. Development rates did not differ between microinjected and control groups (gold nanoparticles: 67.3%, silver nanoparticles: 61.5%, sham: 66.2%, handling control: 79.4%). Real-time PCR analysis of six developmentally important genes (BAX, BCL2L2, TP53, OCT4, NANOG, DNMT3A) did not reveal an influence on gene expression in blastocysts. Contrary to silver nanoparticles, exposure to comparable Ag+-ion concentrations resulted in an immediate arrest of embryo development. In conclusion, the results do not indicate any detrimental effect of colloidal gold or silver nanoparticles on the development of murine embryos. © 2014 Taylor et al; licensee Beilstein-Institut.
    view abstractdoi: 10.3762/bjnano.5.80
  • 2014 • 85 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 • 84 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 • 83 Chemical interactions between silver nanoparticles and thiols: A comparison of mercaptohexanol against cysteine
    Toh, H.S. and Batchelor-Mcauley, C. and Tschulik, K. and Compton, R.G.
    Science China Chemistry 57 1199-1210 (2014)
    The interaction between citrate capped silver nanoparticles and two different thiols, mercaptohexanol (MH) and cysteine, was investigated. The thiols interacted with silver nanoparticles in a significantly contrasting manner. With MH, a sparingly soluble silver(I) thiolate complex AgSRm (Rm = -(CH2)6OH) was formed on the silver nanoparticle surface. Cyclic voltammograms and UV-vis spectra were used to infer that the AgSRm complex on the nanoparticle surface undergoes a phase transition to give a mixture of AgSRm and Ag2S-like complexes. In contrast, when silver nanoparticles were exposed to cysteine, the citrate capping agent on the silver nanoparticles was replaced by cysteine to give cysteine capped nanoparticles. As cysteine capped nanoparticles form, the electrochemical data displayed a decrease in oxidative peak charge but the UV-vis spectra showed a constant signal. Therefore, cysteine capped nanoparticles were suggested to have either inactivated the silver surface or else promoted detachment from the electrode surface. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg.
    view abstractdoi: 10.1007/s11426-014-5141-8
  • 2014 • 82 Interaction of dermatologically relevant nanoparticles with skin cells and skin
    Vogt, A. and Rancan, F. and Ahlberg, S. and Nazemi, B. and Choe, C.S. and Darvin, M.E. and Hadam, S. and Blume-Peytavi, U. and Loza, K. and Diendorf, J. and Epple, M. and Graf, C. and Ruhl, E. and Meinke, M.C. and Lademann, J.
    Beilstein Journal of Nanotechnology 5 2363-2373 (2014)
    The investigation of nanoparticle interactions with tissues is complex. High levels of standardization, ideally testing of different material types in the same biological model, and combinations of sensitive imaging and detection methods are required. Here, we present our studies on nanoparticle interactions with skin, skin cells, and biological media. Silica, titanium dioxide and silver particles were chosen as representative examples for different types of skin exposure to nanomaterials, e.g., unintended environmental exposure (silica) versus intended exposure through application of sunscreen (titanium dioxide) or antiseptics (silver). Because each particle type exhibits specific physicochemical properties, we were able to apply different combinations of methods to examine skin penetration and cellular uptake, including optical microscopy, electron microscopy, X-ray microscopy on cells and tissue sections, flow cytometry of isolated skin cells as well as Raman microscopy on whole tissue blocks. In order to assess the biological relevance of such findings, cell viability and free radical production were monitored on cells and in whole tissue samples. The combination of technologies and the joint discussion of results enabled us to look at nanoparticle-skin interactions and the biological relevance of our findings from different angles. © 2014 Vogt et al.
    view abstractdoi: 10.3762/bjnano.5.245
  • 2014 • 81 Femtogram detection of cytokines in a direct dot-blot assay using SERS microspectroscopy and hydrophilically stabilized Au-Ag nanoshells
    Wang, Y. and Salehi, M. and Schütz, M. and Schlücker, S.
    Chemical Communications 50 2711-2714 (2014)
    Rapid parallel detection of two cytokines (IL-6 and IL-8) with femtogram sensitivity in a simple direct dot-blot assay is demonstrated. The microspectroscopic SERS acquisition scheme employs rationally designed, hydrophilically stabilized Au-Ag nanoshells as SERS labels, which are optimized for signal enhancement upon red laser excitation. © 2014 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3cc48633h
  • 2014 • 80 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 • 79 Interface reactions of Ag@TiO2 nanocomposite films
    Zuo, J. and Rao, J. and Eggeler, G.
    Materials Chemistry and Physics 145 90-98 (2014)
    TiO2 films were sputtered on 100-nm-thick Ag layers at various O2 partial pressures to study forming processes at the interface. The interfacial reactions during the deposition process were investigated by means of transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and UV-vis reflection spectra. The sputtering process led to formation of Ag nanoparticles surrounded by Ag 2O and TiO2 in the TiO2 film matrix as well as on the surface. The presence of oxygen in the plasma resulted in enrichment of silver oxides on the surface and an intermixing of Ag in the TiO2 matrix. The film structures could be explained based on the interplay among the formation of silver oxide, the nucleation and growth of TiO2, as well as the mobility of silver and silver oxides within the growing TiO2 films. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.matchemphys.2014.01.041
  • 2013 • 78 Internal detection of surface plasmon coupled chemiluminescence during chlorination of potassium thin films
    Becker, F. and Krix, D. and Hagemann, U. and Nienhaus, H.
    Journal of Chemical Physics 138 (2013)
    The interaction of chlorine with potassium surfaces is a prototype reaction with a strong non-adiabatic energy transfer leading to exoemission and chemiluminescence. Thin film K/Ag/p-Si(111) Schottky diodes with 8 nm potassium on a 5-200 nm thick Ag layer are used as 2π-photodetectors for the chemiluminescence during chlorination of the K film at 110 K. The observed photocurrent shows a sharp maximum for small exposures and decreases gradually with the increasing chloride layer. The time dependence can be explained by the reaction kinetics, which is governed initially by second-order adsorption processes followed by an electric field-assisted diffusion. The detector current corresponds to a yield of a few percent of elementary charge per reacting chlorine molecule and is orders of magnitude larger than for external detection. The photoyield can be enhanced by increasing the Ag film thickness. For Ag films of 30 and 50 nm, the yield exhibits a maximum indicating surface plasmon coupled chemiluminescence. Surface plasmon polaritons in the Ag layer are excited by the reaction and decay radiatively into Si leading to the observed currents. A model calculation for the reverse process in attenuated total reflection is applied to explain the observed current yield maxima. © 2013 American Institute of Physics.
    view abstractdoi: 10.1063/1.4776156
  • 2013 • 77 Interaction of light and surface plasmon polaritons in Ag Islands studied by nonlinear photoemission microscopy
    Buckanie, N.M. and Kirschbaum, P. and Sindermann, S. and Meyer zu Heringdorf, F.-J.
    Ultramicroscopy 130 49-53 (2013)
    Two photon photoemission microscopy was used to study the interaction of femtosecond laser pulses with Ag islands prepared using different strategies on Si(111) and SiO2. The femtosecond laser pulses initiate surface plasmon polariton (SPP) waves at the edges of the island. The superposition of the electrical fields of the femtosecond laser pulses with the electrical fields of the SPP results in a moiré pattern that is comparable despite the rather different methods of preparation and that gives access to the wavelength and direction of the SPP waves. If the SPPs reach edges of the Ag islands, they can be converted back into light waves. The incident and refracted light waves result in an interference pattern that can again be described with a moiré pattern, demonstrating that Ag islands can be used as plasmonic beam deflectors for light. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2013.03.007
  • 2013 • 76 A disposable sticky electrode for the detection of commercial silver NPs in seawater
    Cheng, W. and Stuart, E.J.E. and Tschulik, K. and Cullen, J.T. and Compton, R.G.
    Nanotechnology 24 (2013)
    The ability to perform efficient and affordable field detection and quantification of nanoparticles in aquatic environmental systems remains a significant technical challenge. Recently we reported a proof of concept of using 'sticky' electrodes for the detection of silver nanoparticles (Tschulik et al 2013 Nanotechnology 29 295502). Now a disposable electrode for detection and quantification of commercial Ag nanoparticles in natural seawater is presented. A disposable screen printed electrode is modified with cysteine and characterized by sticking and stripping experiments, with silver nanoparticle immobilization on the electrode surface and subsequent oxidative stripping, yielding a quantitative determination of the amount of Ag nanoparticles adhering to the electrode surface. The modified electrode was applied to natural seawater to mimic field-based environmental monitoring of Ag NPs present in seawater. The results demonstrated that commercial Ag NPs in natural seawater can be immobilized, enriched and quantified within short time period using the disposable electrodes without any need for elaborate experiments. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/24/50/505501
  • 2013 • 75 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 • 74 Influence of substrate surface-induced defects on the interface state between NaCl(100) and Ag(111)
    Heidorn, S. and Bertram, C. and Koch, J. and Boom, K. and Matthaei, F. and Safiei, A. and Henzl, J. and Morgenstern, K.
    Journal of Physical Chemistry C 117 16095-16103 (2013)
    NaCl islands on Ag(111) are investigated by low temperature scanning tunneling microscopy and spectroscopy. The thermodynamically stable growth mode consists of bilayer-high rectangular-shaped islands that are (100) terminated with a large band gap. Deviations from this bulk-like (100) growth are induced by surface defects as intrinsic step edges and point defects in the supporting Ag(111) surface. The interface between NaCl(100) and Ag(111) induces an interface state that is completely depopulated with its onset at (92 ± 4) meV. The influence of the Ag surface-induced defects on the interface state is discussed. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/jp405297h
  • 2013 • 73 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 • 72 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 • 71 Measurement of the silver ion concentration in wound fluids after implantation of silver-coated megaprostheses: Correlation with the clinical outcome
    Hussmann, B. and Johann, I. and Kauther, M.D. and Landgraeber, S. and Jäger, M. and Lendemans, S.
    BioMed Research International 2013 (2013)
    Background. Tumor patients and patients after traumas are endangered by a reduced immune defense, and a silver coating on their megaprostheses may reduce their risks of infection. The aim of this study was to determine the silver ion concentration directly measured from the periprosthetic tissue and the influence on the clinical outcome. Material and Methods. Silver ions were evaluated in 5 mL wound fluids two days postoperatively and in blood patients 7 and 14 days after surgery using inductively coupled plasma emission spectrometry in 18 patients who underwent total joint replacement with a silver-coated megaendoprosthesis. Results. The concentration of silver ions averaged 0.08 parts per million. Patients who showed an increased silver concentration in the blood postoperatively presented a lower silver concentration in the wound fluids and a delayed decrease in C-reactive protein levels. There were significantly fewer reinfections and shorter hospitalization in comparison with a group that did not receive a silver-coated megaprosthesis. Conclusion. An increased concentration of silver in the immediate surroundings of silver-coated prostheses was demonstrated for the first time in cohorts of patients with trauma or tumors. An elevated concentration of silver ions in the direct periprosthetic tissue may have reduced the infection rate. © 2013 B. Hussmann et al.
    view abstractdoi: 10.1155/2013/763096
  • 2013 • 70 Influence of the substrate bias on the stoichiometry and structure of RF-magnetron sputter-deposited silver-containing calcium phosphate coatings
    Ivanova, A.A. and Surmeneva, M.A. and Grubova, I.Y. and Sharonova, A.A. and Pichugin, V.F. and Chaikina, M.V. and Buck, V. and Prymak, O. and Epple, M. and Surmenev, R.A.
    Materialwissenschaft und Werkstofftechnik 44 218-225 (2013)
    A coating on the basis of silver-containing hydroxyapatite (silver-hydroxyapatite) was deposited by radio frequency (RF) magnetron sputtering. X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and ellipsometry were used to analyse the change in structure and stoichiometry of the coatings upon the change of the negative electrical bias (-50 V and -100 V) on the substrate. The chemical composition of the sputter-deposited coating was identical to the target. However, an increase in the negative electrical bias on the substrate led to a decrease of the coating thickness. In addition, the average size of the grains decreased from 55 ± 15 nm (grounded substrate) up to 30 ± 10 nm when an electrical bias of -100 V was applied. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201300101
  • 2013 • 69 Simulation of shear banding in heterophase co-deformation: Example of plane strain compressed Cu-Ag and Cu-Nb metal matrix composites
    Jia, N. and Roters, F. and Eisenlohr, P. and Raabe, D. and Zhao, X.
    Acta Materialia 61 4591-4606 (2013)
    The co-deformation and shear localization in heterophase alloys is studied using two-dimensional crystal plasticity finite element simulations on plane strain compressed Cu-Ag and Cu-Nb metal matrix composites. The aim is to study the fundamentals of micromechanics, co-deformation and shear banding in materials with heterophase interfaces. It is observed that, depending on the initial orientations of the crystals, co-deformation of the constituent heterophases often proceeds via collective mechanisms, i.e. by pronounced shear banding triggered by stress concentration at the interfaces. This phenomenon leads to highly localized strains within the bands, exceeding the average strain in part by two orders of magnitude. Shear band development is related to the inherent mechanical properties of each crystal and also to the properties of the abutting crystals. The predicted topology and nature of the cross-phase shear bands, i.e. the extreme local strains, significant bending of the interface regions, and sharp strain localization that propagates across the interfaces, agree well with experimental observations in cold-rolled composites. The simulations reveal that cross-phase shear banding leads to large and highly localized values of stress and strain at heterophase interfaces. Such information is essential for a better understanding of the micromechanical boundary conditions inside co-deformed composites and the associated shear-induced chemical mixing. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2013.04.029
  • 2013 • 68 Self-learning kinetic Monte Carlo model for arbitrary surface orientations
    Latz, A. and Brendel, L. and Wolf, D.E.
    Materials Research Society Symposium Proceedings 1559 36-41 (2013)
    While the self-learning kinetic Monte Carlo (SLKMC) method enables the calculation of transition rates from a realistic potential, implementations of it were usually limited to one specific surface orientation. An example is the fcc (111) surface in Latz et al. 2012, J. Phys.: Condens. Matter 24, 485005. This work provides an extension by means of detecting the local orientation, and thus allows for the accurate simulation of arbitrarily shaped surfaces. We applied the model to the diffusion of Ag monolayer islands and voids on a Ag(111) and Ag(001) surface, as well as the relaxation of a three-dimensional spherical particle. © 2013 Materials Research Society.
    view abstractdoi: 10.1557/opl.2013.691
  • 2013 • 67 Coupling osmium complexes to epoxy-functionalised polymers to provide mediated enzyme electrodes for glucose oxidation
    Ó Conghaile, P. and Pöller, S. and MacAodha, D. and Schuhmann, W. and Leech, D.
    Biosensors and Bioelectronics 43 30-37 (2013)
    Newly synthesised osmium complex-modified redox polymers were tested for potential application as mediators in glucose oxidising enzyme electrodes for application to biosensors or biofuel cells. Coupling of osmium complexes containing amine functional groups to epoxy-functionalised polymers of variable composition provides a range of redox polymers with variation possible in redox potential and physicochemical properties. Properties of the redox polymers as mediators for glucose oxidation were investigated by co-immobilisation onto graphite with glucose oxidase or FAD-dependent glucose dehydrogenase using a range of crosslinkers and in the presence and absence of multiwalled carbon nanotubes. Electrodes prepared by immobilising [P20-Os(2,2'-bipyridine)2(4-aminomethylpyridine)Cl].PF6, carbon nanotubes and glucose oxidase exhibit glucose oxidation current densities as high as 560μAcm-2 for PBS containing 100mM glucose at 0.45V vs. Ag/AgCl. Films prepared by crosslinking [P20-Os(4,4'-dimethoxy-2,2'-bipyridine)2(4-aminomethylpyridin e)Cl].PF6, an FAD-dependent glucose dehydrogenase, and carbon nanotubes achieve current densities of 215μAcm-2 in 5mM glucose at 0.2V vs. Ag/AgCl, showing some promise for application to glucose oxidising biosensors or biofuel cells. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2012.11.036
  • 2013 • 66 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 • 65 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 • 64 Laser-based generation of nanocomposites without matrix-coupling agents for bioactive medical devices
    Schwenke, A. and Wagener, P. and Weiß, A. and Klimenta, K. and Wiegel, H. and Sajti, L. and Barcikowski, S.
    Chemie-Ingenieur-Technik 85 740-746 (2013)
    New production technologies are required to benefit of the full potential of nanocomposites by homogeneous dispersion of nanoparticles along the process chain. Synthesis of silver nanoparticles by laser ablation in liquid and their integration into polymers are presented. Antibacterial properties of these materials and processability into prototypes for medical devices with antibacterial protection are demonstrated. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cite.201200035
  • 2013 • 63 Lattice dependent motion of voids during electromigration
    Sindermann, S.P. and Latz, A. and Dumpich, G. and Wolf, D.E. and Meyer zu Heringdorf, F.-J.
    Journal of Applied Physics 113 (2013)
    The influence of the crystal lattice configuration to electromigration processes, e.g., void formation and propagation, is investigated in suitable test structures. They are fabricated out of self-assembled, bi-crystalline Ag islands, grown epitaxially on a clean Si(111) surface. The μm-wide and approximately 100 nm thick Ag islands are a composition of a Ag(001) and a Ag(111) part. By focused ion beam milling, they are structured into wires with a single grain boundary, the orientation of which can be chosen arbitrarily. In-situ scanning electron microscopy (SEM) allows to capture an image sequence during electrical stressing and monitors the development of voids and hillocks in time. To visualize the position and motion of voids, we calculate void maps using a threshold algorithm. Most of the information from the SEM image sequence is compressed into one single image. Our present electromigration studies are based on in-situ SEM investigations for three different lattice configurations: Ag(001) (with electron current flow in [110] direction), Ag(111) (with electron current flow in [112] direction), and additionally 90°rotated Ag(111) (with electron current flow in [110] direction). Our experimental results show that not only the formation and shape but also the motion direction of voids strongly depends on the crystal orientation. © 2013 American Institute of Physics.
    view abstractdoi: 10.1063/1.4798367
  • 2013 • 62 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 • 61 Electrochemical detection of commercial silver nanoparticles: Identification, sizing and detection in environmental media
    Stuart, E.J.E. and Tschulik, K. and Omanović, D. and Cullen, J.T. and Jurkschat, K. and Crossley, A. and Compton, R.G.
    Nanotechnology 24 (2013)
    The electrochemistry of silver nanoparticles contained in a consumer product has been studied. The redox properties of silver particles in a commercially available disinfectant cleaning spray were investigated via cyclic voltammetry before particle-impact voltammetry was used to detect single particles in both a typical aqueous electrolyte and authentic seawater media. We show that particle-impact voltammetry is a promising method for the detection of nanoparticles that have leached into the environment from consumer products, which is an important development for the determination of risks associated with the incorporation of nanotechnology into everyday products. © 2013 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/24/44/444002
  • 2013 • 60 Ag-stabilized few-layer graphene dispersions in low boiling point solvents for versatile nonlinear optical applications
    Sun, Z. and Dong, N. and Wang, K. and König, D. and Nagaiah, T.C. and Sánchez, M.D. and Ludwig, Al. and Cheng, X. and Schuhmann, W. and Wang, J. and Muhler, M.
    Carbon 62 182-192 (2013)
    A solution stabilization strategy that uses an easily removable media is critical to graphene (G) applications. Here, we demonstrate that highly stable graphene dispersions in low boiling point solvents such as isopropanol can be readily achieved by the uniform deposition of Ag nanoparticles (NPs) on the surface of graphene. Optimizing the synthesis parameters such as ultrasonic intensity, feeding strategy, loading content and precursor concentration allowed us to tune the particle size and, in this way, the stabilizing effects of the NPs on the dispersions. The as-obtained Ag/G/i-PrOH dispersions exhibit versatile nonlinear optical properties suggesting a great potential in nanophotonic applications such as absorber for ultrafast lasers and eye protection. © 2013 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.carbon.2013.06.010
  • 2013 • 59 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 • 58 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 • 57 '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 • 56 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 • 55 Electron transport at surfaces and interfaces
    Bobisch, C.A. and Möller, R.
    Chimia 66 23-30 (2012)
    Here we present two techniques which give insight on transport phenomena with atomic resolution. Ballistic electron emission microscopy is used to study the ballistic transport through layered heterogeneous systems. The measured ballistic fraction of the tunneling current provides information about lossless transport channels through metallic layers and organic adsorbates. The transport characteristics of Bi(111)/Si Schottky devices and the influence of the organic adsorbates perylene tetracaboxylic dianhydride acid and C 60 on the ballistic current are discussed. Scanning tunneling potentiometry gives access to the lateral transport along a surface, thus scattering processes within two-dimensional electron systems for the Bi(111) surface and the Si(111)(√3×√3)-Ag surface could be visualized. © Schweizerische Chemische Gesellschaft.
    view abstractdoi: 10.2533/chimia.2012.23
  • 2012 • 54 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 • 53 Serum albumin reduces the antibacterial and cytotoxic effects of hydrogel-embedded colloidal silver nanoparticles
    Grade, S. and Eberhard, J. and Neumeister, A. and Wagener, P. and Winkel, A. and Stiesch, M. and Barcikowski, S.
    RSC Advances 2 7190-7196 (2012)
    Although silver nanoparticles (AgNPs) are widely used as ion-releasing antimicrobial additives in medical devices, recent reports indicate the suppression of effectiveness in the presence of blood serum proteins. Bovine serum albumin (BSA) is known to bind silver and silver ions, so that the presence of proteins may change the antibacterial or cytotoxic properties of AgNPs even when they are embedded in a solid agar hydrogel matrix. We produced ligand-free AgNPs by laser ablation in water resulting in aqueous silver mass concentrations of 0.5 to 7.1%. The AgNPs were immersed into agar in concentrations of 5-70 μg ml -1 medium. We examined the influence of 1% BSA within the hydrogel matrix on the nanoparticles' antibacterial effect on four clinically relevant bacteria strains and the cytotoxicity of colloidal AgNP was tested on fibroblasts with or without 1% BSA. The hydrogel-immobilized AgNPs showed a significant reduction of antibacterial activity in the presence of BSA. Cytotoxicity started at a colloidal AgNP concentration of 35 μg ml -1, and addition of BSA significantly reduced the effect on cell morphology and viability. Overall, in the presence of BSA, both antibacterial and cytotoxic effects of AgNPs were markedly reduced. Notably, a therapeutic AgNP window, requiring a dose at which pathogenic bacteria growth is inhibited while fibroblast viability is not affected, could only be observed in the absence of BSA. Addition of BSA reduces the antibacterial activity of AgNP to a point without significant growth inhibition of S. aureus but still observable cytotoxic effects on HGFib. Hence, the presence of a major blood serum protein significantly decreases the antimicrobial effects of AgNPs on a range of pathogenic bacteria even when the NPs are immobilized within an agar hydrogel model. © 2012 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c2ra20546g
  • 2012 • 52 Therapeutic window of ligand-free silver nanoparticles in agar-embedded and colloidal state: In vitro bactericidal effects and cytotoxicity
    Grade, S. and Eberhard, J. and Wagener, P. and Winkel, A. and Sajti, C.L. and Barcikowski, S. and Stiesch, M.
    Advanced Engineering Materials 14 B231-B239 (2012)
    The inhibition of bacterial growth through effective non-toxic antimicrobial substances is of great importance for the prevention and therapy of implant infections in various medical disciplines. For the evaluation of a therapeutic window of silver nanoparticles (AgNPs), their bactericidal properties were tested in agar composites and colloids on four medical relevant bacteria. Therefore, we produced AgNPs using high-power nanosecond laser ablation in water showing a log-normal particle diameter distribution centered at 17 nm. Bacteria were incubated with AgNP concentrations ranging from 5 to 70 μg · mL -1 and the growth rate was recorded. Additionally, cytotoxic effects of AgNPs on human gingival fibroblasts were examined. The experiments demonstrated that laser-synthesized AgNPs resulted in a significant bacterial growth inhibition of more than 80% at the indicated concentrations in a solid agar model (Pseudomonas aeruginosa 10 μg · mL -1, Streptococcus salivarius 10 μg · mL -1, Escherichia coli 20 μg · mL -1, Staphylococcus aureus 70 μg · mL -1). In a planktonic bacteria model, the growth of the tested bacteria was significantly delayed by the addition of AgNPs at a concentration of 35 μg · mL -1. The cytotoxic assays showed limited adverse effects on human fibroblasts at concentrations of less than 20 μg · mL -1. The present study illustrates the strong antibacterial effects of ligand-free, laser-generated AgNPs that exhibit moderate cytotoxic effects, resulting in a therapeutically applicable concentration of AgNPs for medical purposes between 10 and 20 μg · mL -1. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201180016
  • 2012 • 51 The toxic effect of silver ions and silver nanoparticles towards bacteria and human cells occurs in the same concentration range
    Greulich, C. and Braun, D. and Peetsch, A. and Diendorf, J. and Siebers, B. and Epple, M. and Köller, M.
    RSC Advances 2 6981-6987 (2012)
    Silver is commonly used both in ionic form and in nanoparticulate form as a bactericidal agent. This is generally ascribed to a higher toxicity towards prokaryotic cells than towards mammalian cells. Comparative studies with both silver ions (such as silver acetate) and polyvinylpyrrolidone (PVP)-stabilized silver nanoparticles (70 nm) showed that the toxic effect of silver occurs in a similar concentration range for Escherichia coli, Staphylococcus aureus, human mesenchymal stem cells (hMSCs), and peripheral blood mononuclear cells (PBMCs), i.e. 0.5 to 5 ppm for silver ions and 12.5 to 50 ppm for silver nanoparticles. For a better comparison, bacteria were cultivated both in Lysogeny broth medium (LB) and in Roswell Park Memorial Institute medium (RPMI)/10% fetal calf serum (FCS) medium, as the state of silver ions and silver nanoparticles may be different due to the presence of salts, and biomolecules like proteins. The effective toxic concentration of silver towards bacteria and human cells is almost the same. © 2012 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c2ra20684f
  • 2012 • 50 Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core-shell nanocontainers for metal nanoparticles
    Ho, C.H. and Thiel, M. and Celik, S. and Odermatt, E.K. and Berndt, I. and Thomann, R. and Tiller, J.C.
    Polymer (United Kingdom) 53 4623-4630 (2012)
    Hyperbranched amphiphilic polymeric systems with core-shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30-0.32. The molecular weight M n could be controlled in a range of 5000-12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core-shell systems. © 2012 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.polymer.2012.08.032
  • 2012 • 49 Current induced surface diffusion on a single-crystalline silver nanowire
    Kaspers, M.R. and Bernhart, A.M. and Bobisch, C.A. and Möller, R.
    Nanotechnology 23 (2012)
    Scanning tunnelling microscopy was used to study the morphological changes of the surface of a single-crystalline silver nanowire caused by a lateral electron current. At current densities of about 1.5×10 7 A cm -2, surface atoms are extracted from step edges, resulting in the motion of surface steps, islands and holes with a thickness or depth of one monolayer. Upon current reversal the direction of the material transport can be altered. The findings are interpreted in terms of the wind force. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0957-4484/23/20/205706
  • 2012 • 48 A three-dimensional self-learning kinetic Monte Carlo model: Application to Ag(111)
    Latz, A. and Brendel, L. and Wolf, D.E.
    Journal of Physics Condensed Matter 24 (2012)
    The reliability of kinetic Monte Carlo (KMC) simulations depends on accurate transition rates. The self-learning KMC method (Trushin etal 2005 Phys.Rev.B 72 115401) combines the accuracy of rates calculated from a realistic potential with the efficiency of a rate catalog, using a pattern recognition scheme. This work expands the original two-dimensional method to three dimensions. The concomitant huge increase in the number of rate calculations on the fly needed can be avoided by setting up an initial database, containing exact activation energies calculated for processes gathered from a simpler KMC model. To provide two representative examples, the model is applied to the diffusion of Ag monolayer islands on Ag(111), and the homoepitaxial growth of Ag on Ag(111) at low temperatures. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/24/48/485005
  • 2012 • 47 Simulation of electromigration effects on voids in monocrystalline Ag
    Latz, A. and Wolf, D.E.
    Materials Research Society Symposium Proceedings 1428 1-6 (2012)
    Understanding electromigration effects in monocrystalline metal becomes of increasing interest with decreasing width and thickness of interconnects. Using a three-dimensional, atomistic model based on the Kinetic Monte Carlo method, we investigate voids in monocrystalline silver. Subject to electromigration, voids begin to drift. We show that the drift velocity not only depends on the void size, but also on the electromigration force direction, with respect to the crystallographic orientation. © 2012 Materials Research Society.
    view abstractdoi: 10.1557/opl.2012.1099
  • 2012 • 46 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 • 45 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 • 44 Coulomb attraction during the carpet growth mode of NaCl
    Matthaei, F. and Heidorn, S. and Boom, K. and Bertram, C. and Safiei, A. and Henzl, J. and Morgenstern, K.
    Journal of Physics Condensed Matter 24 (2012)
    The submonolayer growth of NaCl bilayer high-rectangular shaped islands on Ag(111) is investigated at around room temperature by using low temperature scanning tunneling microscopy. The growth at the step edges is preferred. Two kinds of islands are observed. They either grow with their non-polar edge at the step edge of Ag(111) or the islands overgrow in a carpet-like mode with the polar direction parallel to the edge. In the latter case, the Ag step is rearranged and considerable, while the NaCl layer is bent. This study clarifies the nature of the interaction of an alkali halide nanostructure with a metal step edge. © 2012 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/24/35/354006
  • 2012 • 43 Ag/ZnO nanomaterials as high performance sensors for flammable and toxic gases
    Simon, Q. and Barreca, D. and Gasparotto, A. and MacCato, C. and Tondello, E. and Sada, C. and Comini, E. and Devi, A. and Fischer, R.A.
    Nanotechnology 23 (2012)
    Ag/ZnO nanocomposites supported on polycrystalline Al 2O 3 were synthesized by an unprecedented approach combining plasma enhanced chemical vapor deposition (PE-CVD) of ZnO matrices and the subsequent deposition of Ag nanoparticles (NPs) by radio frequency (RF) sputtering. The system structure, composition and morphology were investigated by glancing incidence x-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDXS). A tailored dispersion and distribution of silver particles could be obtained under mild conditions by the sole variation of the sputtering time. Gas sensing properties toward flammable and toxic gases, both reducing (CH 3CH 2OH, CH 3COCH 3) and oxidizing (O 3), were investigated in the temperature range 100400°C. Beside the high sensitivity, the developed sensors exhibited a response proportional to Ag content, thanks to catalytic and electronic effects promoted by silver NPs. In addition, discrimination between oxidizing and reducing analytes was enabled by a suitable choice of the adopted working temperature.
    view abstractdoi: 10.1088/0957-4484/23/2/025502
  • 2012 • 42 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 • 41 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 • 40 Simultaneous acquisition of impedance and gravimetric data in a cyclic potential scan for the characterization of nonstationary electrode/electrolyte interfaces
    Berkes, B.B. and Maljusch, A. and Schuhmann, W. and Bondarenko, A.S.
    Journal of Physical Chemistry C 115 9122-9130 (2011)
    Simultaneous acquisition of electrochemical impedance spectroscopy and quartz crystal microbalance (EIS-EQCM) data in cyclic electrode potential scans was used to characterize nonstationary underpotential deposition (UPD) of atomic layers of Ag on Au and Cu on Pt. Both EIS and EQCM data sets complemented each other in the elucidation of interface models and the investigation of different aspects of the interfacial dynamics. EIS-EQCM provided an opportunity to monitor coadsorption and competitive adsorption of anions during the Ag and Cu UPD using (i) the electrode mass change, (ii) adsorption capacitances, and (iii) double-layer capacitances. Kinetic information is available in the EIS-EQCM through the charge transfer resistances and apparent rate coefficients. The latter expresses the rate of UPD into the partially covered electrode surface. The apparent rate coefficients for the Ag UPD were determined to vary from 0.15 to 0.45 cm/s which is between the standard constant rates k0 of Ag bulk deposition on Ag reported previously for different Ag surfaces. Cu UPD on Pt and Ag UPD on Au contributed differently into a resonance resistance ?R(E) available from the EQCM data sets. Spontaneous surface alloying between Ag and Au during the Ag UPD continuously increased the ?R, while the Cu overlayer formation on Pt as well as experiments without Ag+ and Cu 2+ in the solution did not change this parameter significantly. The EIS-EQCM appeared to be a promising tool for an improved characterization and understanding of nonstationary electrochemical interfaces. © 2011 American Chemical Society.
    view abstractdoi: 10.1021/jp200755p
  • 2011 • 39 Shape transformation mechanism of silver nanorods in aqueous solution
    Damm, C. and Segets, D. and Yang, G. and Vieweg, B.F. and Spiecker, E. and Peukert, W.
    Small 7 147-156 (2011)
    The spontaneous shape transformation of silver nanorods with an initial length of several hundred nanometers towards spherical particle shapes in aqueous solution is investigated by means of scanning electron microscopy, UV-vis absorption spectroscopy, anodic stripping voltammetry, and high-resolution transmission electron microscopy (HRTEM). The consolidation of the results reveals an increase in the particle number density with time. Moreover, HRTEM image analysis along the cross section of the rods evidences the presence of fivefold twinning defects which extend along the whole rod length. According to the analytical model of Monk et al. this kind of rod structure is only thermodynamically stable if the rod length is below a critical value at a given diameter. The rods investigated in the present work do not fulfill the stability criterion as they exceed the critical length. Thus, the rods decay into smaller "nanobuns" and defective as well as defect-free spheres. A mechanism based on findings from the literature, HRTEM image analysis of former rods, transition states, and the final particle structures is proposed. The defects along the surface are seen as starting points for the dissolution of material, which is reintegrated into the solid phase by homogeneous as well as heterogeneous nucleation and growth. The decay process of silver nanorods in aqueous suspension is investigated. During ageing the aspect ratio decreases with time whereas the absolute particle number increases. Defects play a decisive role in rod decay and underline how crystal structure influences particle shape. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201001600
  • 2011 • 38 Templated synthesis of shape-controlled, ordered TiO 2 cage structures
    Deng, Y. and Tüysüz, H. and Henzie, J. and Yang, P.
    Small 7 2037-2040 (2011)
    Based on a combination of colloidal self-assembly and atomic layer deposition, a facile approach is developed to create novel, high-quality, ordered cage structures of anatase TiO 2 with shape and morphology control using Ag nanocrystals of different shapes as templates. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/smll.201100579
  • 2011 • 37 Thermodynamic modelling of the Ag-Cu-Ti ternary system
    Dezellus, O. and Arroyave, R. and Fries, S.G.
    International Journal of Materials Research 102 286-297 (2011)
    The Ag-Cu-Ti system is important for brazing applications, particularly for ceramic joining. This system is characterized by numerous intermetallics in the Cu-Ti binary and the existence of a miscibility gap in the liquid phase. For applications, knowledge of the phase equilibria, invariant reactions in the temperature range of interest and thermodynamic activity values (mainly of Ti) are important. Thermodynamic model parameters for all the stable phases in the Ag-Cu, Cu-Ti and Ag-Ti systems, previously obtained using the Calphad method and available in the literature are used. A new thermodynamic description for the ternary interaction parameter of the liquid is obtained from experimental informations. Ti 2Cu and Ti 2Ag which have the same crystallographic structure were modelled as a single phase. The same was done for TiCu and TiAg. Finally, solid solubility of Ag in the Ti-Cu intermetallics is taken into account. The parameters obtained in this assessment are later used for the calculation of selected sections that can be useful for research and applications in the field of joining with Ti-activated Ag-Cu braze. © Carl Hanser Verlag GmbH & Co. KG.
    view abstractdoi: 10.3139/146.110472
  • 2011 • 36 A molecular dynamics investigation of kinetic electron emission from silver surfaces under varying angle of projectile impact
    Duvenbeck, A. and Hanke, S. and Weidtmann, B. and Wucher, A.
    Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 269 1661-1664 (2011)
    We present a computer simulation study on the influence of the impact angle of the projectile on kinetic electron emission yields for 5-keV Ag → Ag bombardment. By means of a hybrid computer simulation model incorporating (i) the particle dynamics following the primary particle impact, (ii) the kinetically induced electronic substrate excitations via electronic friction and electron promotion and (iii) the transport of excitation energy away from the spot of generation, a full three-dimensional electron temperature profile within the volume affected by the atomic collision cascade is calculated. This profile is evaluated at the very surface of the target and taken as input for a thermionic model ('hot-spot-model') for kinetic electron emission. Averaging the results for different choices of the polar angle of incidence Θ over a large set of impact points, the obtained kinetic electron emission yields can be compared with experimental data and predictions from simple geometrical calculations. The presented simulation results appear to be reasonable in comparison with experimental data as well as with simple geometrical considerations of kinetic electron emission under oblique incidence. © 2010 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.nimb.2010.11.082
  • 2011 • 35 Structure, morphology, and aging of Ag-Fe dumbbell nanoparticles
    Elsukova, A. and Li, Z.-A. and Möller, C. and Spasova, M. and Acet, M. and Farle, M. and Kawasaki, M. and Ercius, P. and Duden, T.
    Physica Status Solidi (A) Applications and Materials Science 208 2437-2442 (2011)
    Dumbbell-shaped or Janus-type nanocomposites provide multifunctional properties with various diagnostic and therapeutic applications in biomedicine. We have prepared dumbbell Ag-Fe nanoparticles by magnetron sputtering with subsequent in-flight annealing. Structural properties and chemical compositions of freshly prepared and 5-month aged particles were examined by means of transmission electron microscopy including high-resolution imaging, energy dispersive X-ray spectroscopy, and 3D electron tomography. Fresh particles consist of a faceted Ag part on a Fe-Fe 3O 4 composite particle of more spherical shape. Aging changes the crystallinity and morphology of the particles. The aged nanocomposite consists of a silver spherical particle that is attached to a hollow iron oxide sphere containing one or several silver clusters inside. TEM images of the fresh (a) and aged (b) Ag-Fe nanoparticles. (c) 3D reconstructed image of an aged Ag-Fe particle with color segmentation. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.201127104
  • 2011 • 34 Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles
    Gebauer, J.S. and Treuel, L.
    Journal of Colloid and Interface Science 354 546-554 (2011)
    The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs. © 2010 Elsevier Inc.
    view abstractdoi: 10.1016/j.jcis.2010.11.016
  • 2011 • 33 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 • 32 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 • 31 Metal ion release kinetics from nanoparticle silicone composites
    Hahn, A. and Brandes, G. and Wagener, P. and Barcikowski, S.
    Journal of Controlled Release 154 164-170 (2011)
    Metal ion release kinetics from silver and copper nanoparticle silicone composites generated by laser ablation in liquids are investigated. The metal ion transport mechanism is studied by using different model equations and their fit to experimental data. Results indicate that during the first 30 days of immersion, Fickian diffusion is the dominant transport mechanism. After this time period, the oxidation and dissolution of nanoparticles from the bulk determine the ion release. This second mechanism is very slow since the dissolution of the nanoparticle is found to be anisotropic. Silver ion release profile is best described by pseudo-first order exponential equation. Copper ion release profile is best described by a second order exponential equation. For practical purposes, the in vitro release characteristics of the bioactive metal ions are evaluated as a function of nanoparticle loading density, the chemistry and the texture of the silicone. Based on the proposed two-step release model, a prediction of the release characteristics over a time course of 84 days is possible and a long-term ion release could be demonstrated. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jconrel.2011.05.023
  • 2011 • 30 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 • 29 Transient (000)-order attenuation effects in ultrafast transmission electron diffraction
    Ligges, M. and Rajkovi, I. and Streubhr, C. and Brazda, T. and Zhou, P. and Posth, O. and Hassel, C. and Dumpich, G. and Von Der Linde, D.
    Journal of Applied Physics 109 (2011)
    We discuss the observation of a transient (000)-order attenuation in time-resolved transmission electron diffraction experiments. It is shown that this effect causes a decrease of the diffraction intensity of all higher diffraction orders. This effect is not unique to specific materials as it was observed in thin Au, Ag and Cu films. © 2011 American Institute of Physics.
    view abstractdoi: 10.1063/1.3554405
  • 2011 • 28 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 • 27 Possibilities and limitations of different analytical methods for the size determination of a bimodal dispersion of metallic nanoparticles
    Mahl, D. and Diendorf, J. and Meyer-Zaika, W. and Epple, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 377 386-392 (2011)
    Silver nanoparticles (about 70. nm) and gold nanoparticles (about 15. nm) were prepared and colloidally stabilized with poly(vinylpyrrolidone) (PVP). The pure nanoparticles as well as a 1:1 mixture (w:w) were analysed with a variety of methods which probe the size distribution: Scanning electron microscopy, transmission electron microscopy, dynamic light scattering, analytical disc centrifugation, and Brownian motion analysis (nanoparticle tracking analysis). The differences between the methods are highlighted and their ability to distinguish between silver and gold nanoparticles in the mixture is demonstrated. The size distribution data from the different methods were clearly different, therefore it is recommended to apply more than one method to characterize the nanoparticle dispersion. In particular, the smaller particles were undetectable by dynamic light scattering and nanoparticle tracking analysis in the presence of the large particles. For the 1:1 mixture, only electron microscopy and analytical disc centrifugation were able to give quantitative data on the size distribution. On the other hand, it is not possible to make statements about an agglomeration in dispersion with electron microscopy because an agglomeration may also have occurred during the drying process. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfa.2011.01.031
  • 2011 • 26 Small-scale deposition of thin films and nanoparticles by microevaporation sources
    Meyer, R. and Hamann, S. and Ehmann, M. and König, D. and Thienhaus, S. and Savan, A. and Ludwig, Al.
    Journal of Microelectromechanical Systems 20 21-27 (2011)
    This paper reports on a novel miniaturized deposition technique based on micro-hotplates which are used as microevaporation sources (MES) for a localized deposition of thin films and nanoparticles. The feasibility of this small-scale deposition technique and its general properties are shown for depositions of Ag on unpatterned and microstructured substrates. The deposited films are rotationally symmetric and show a distinct lateral thickness change. We take advantage of this latter effect, as, e.g., all stages of film condensation can be observed within one experiment on one sample, in a size suitable for transmission electron microscopy investigations. For realizing the most laterally confined depositions, a micro-Knudsen cell was used. It is shown that the use of MES is also very suitable for the fabrication and deposition of nanoparticles. © 2011 IEEE.
    view abstractdoi: 10.1109/JMEMS.2010.2090506
  • 2011 • 25 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 • 24 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 • 23 Probing the Pt Surface for Oxygen Reduction by Insertion of Ag
    Schwamborn, S. and Bron, M. and Schuhmann, W.
    Electroanalysis 23 588-594 (2011)
    We report on the probing of the Pt surface for oxygen reduction reaction (ORR) by insertion of Ag. Therefore, PtAg bimetallic nanoparticles were prepared by pulse electrodeposition. In a second step, Ag was electro-dissolved in acidic media from the particles under formation of Pt skeleton. The ORR activity of these Pt skeleton depends on two factors: (1) on the surface properties of the Pt-shell and (2) on the electronic as well as geometric influences of the remaining Ag in the particle core. By varying the conditioning procedure prior to measuring the ORR activity, we were able to differentiate between these two effects. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/elan.201000510
  • 2011 • 22 Influence of processing time on nanoparticle generation during picosecond-pulsed fundamental and second harmonic laser ablation of metals in tetrahydrofuran
    Schwenke, A. and Wagener, P. and Nolte, S. and Barcikowski, S.
    Applied Physics A: Materials Science and Processing 104 77-82 (2011)
    The influence of fundamental and second harmonic wavelength on ablation efficiency and nanoparticle properties is studied during picosecond laser ablation of silver, zinc, and magnesium in polymer-doped tetrahydrofuran. Laser ablation in stationary liquid involves simultaneously the fabrication of nanoparticles by ablation of the target material and fragmentation of dispersed nanoparticles by post irradiation. The ratio in which the laser pulse energy contributes to these processes depends on laser wavelength and colloidal properties. For plasmon absorbers (silver), using the second harmonic wavelength leads to a decrease of the nanoparticle productivity over process time along with exponential decrease in particle diameter, while using the fundamental wavelength results in a constant ablation rate and linear decrease in particle diameter. For colloids made of materials without plasmon absorption (zinc, magnesium), laser scattering is the colloidal property that limits nanoparticle productivity by Mie-scattering of dispersed nanoparticle clusters. © 2011 The Author(s).
    view abstractdoi: 10.1007/s00339-011-6398-9
  • 2011 • 21 Plasma-assisted synthesis of Ag/ZnO nanocomposites: First example of photo-induced H2 production and sensing
    Simon, Q. and Barreca, D. and Bekermann, D. and Gasparotto, A. and MacCato, C. and Comini, E. and Gombac, V. and Fornasiero, P. and Lebedev, O.I. and Turner, S. and Devi, A. and Fischer, R.A. and Van Tendeloo, G.
    International Journal of Hydrogen Energy 36 15527-15537 (2011)
    Ag/ZnO nanocomposites were developed by a plasma-assisted approach. The adopted strategy exploits the advantages of Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) for the growth of columnar ZnO arrays on Si(100) and Al 2O3 substrates, in synergy with the infiltration power of the Radio Frequency (RF)-sputtering technique for the subsequent dispersion of different amounts of Ag nanoparticles (NPs). The resulting composites, both as-prepared and after annealing in air, were thoroughly characterized with particular attention on their morphological organization, structure and composition. For the first time, the above systems have been used as catalysts in the production of hydrogen by photo-reforming of alcoholic solutions, yielding a stable H2 evolution even by the sole use of simulated solar radiation. In addition, Ag/ZnO nanocomposites presented an excellent response in the gas-phase detection of H2, opening attractive perspectives for advanced technological applications. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.ijhydene.2011.09.045
  • 2011 • 20 Compatibilization of laser generated antibacterial Ag- and Cu-nanoparticles for perfluorinated implant materials
    Stelzig, S.H. and Menneking, C. and Hoffmann, M.S. and Eisele, K. and Barcikowski, S. and Klapper, M. and Müllen, K.
    European Polymer Journal 47 662-667 (2011)
    The production of silver and copper particles by laser ablation in an organic solvent and their in situ functionalization with amphiphilic copolymers bearing fluorinated side chains is presented. Aside the stabilization of the particles, the fluorinated side chains render the modified particles compatible with a perfluorinated matrix, which results in a homogeneous distribution of the particles in the matrix. The incorporation of silver particles in perfluorinated matrices is of special interest for the preparation of antibacterial composites, e.g. PTFE, which might be applied in antibacterial implants, e.g. antibacterial vascular prostheses. Laser ablation in liquids as a general method to produce charged nanoparticles of any metal is hence combined with sophisticated surface active compounds. © 2010 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.eurpolymj.2010.10.018
  • 2011 • 19 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
  • 2011 • 18 Shape, orientation, and crystalline composition of silver islands on Si(111)
    Wall, D. and Tikhonov, S. and Sindermann, S. and Spoddig, D. and Hassel, C. and Horn-von Hoegen, M. and Meyer zu Heringdorf, F.-J.
    IBM Journal of Research and Development 55 (2011)
    Photoemission electron microscopy and spot profile analyzing low-energy electron diffraction have been used to study the temperature-dependent growth of Ag islands on a Si(111) surface. Depending on growth temperature, various island shapes can be formed. At low temperatures, polygonic islands are formed, consisting of both Ag(001) and Ag(111) crystal orientations. At higher temperatures, islands consist mostly of Ag(111) orientation and are predominantly of triangular shape. As the islands grow, it is possible that the crystalline composition of an island changes. We observed that Ag(001)-oriented areas convert into areas of Ag(111) orientation. The rotational orientation of the Ag islands with respect to the substrate is explained by a modified coincidence-site lattice approach. © Copyright 2011 by International Business Machines Corporation.
    view abstractdoi: 10.1147/JRD.2011.2158761
  • 2010 • 17 Softlithographic, partial integration of surface-active nanoparticles in a PDMS matrix for microfluidic biodevices
    Demming, S. and Hahn, A. and Edlich, A. and Franco-Lara, E. and Krull, R. and Barcikowski, S. and Büttgenbach, S.
    Physica Status Solidi (A) Applications and Materials Science 207 898-903 (2010)
    The mergence of microfluidics and nanocomposite materials and their in situ structuring leads to a higher integration level within microsystems technology. Nanoparticles (Cu and Ag) produced via laser radiation were suspended in Poly(dimethylsiloxane) to permanently modify surface material. A microstructuring process was implemented which allows the incorporation of these nanomaterials globally or partially at defined locations within a microbioreactor (MBR) for the determination of their antiseptic and toxic effects on the growth of biomass. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssa.200983311
  • 2010 • 16 Penetration of thin C 60 films by metal nanoparticles
    Duffe, S. and Grönhagen, N. and Patryarcha, L. and Sieben, B. and Yin, C. and Von Issendorff, B. and Moseler, M. and Hövel, H.
    Nature Nanotechnology 5 335-339 (2010)
    Metal nanoparticles supported by thin films are important in the fields of molecular electronics, biotechnology and catalysis, among others. Penetration of these nanoparticles through their supporting films can be undesirable in some circumstances but desirable in others, and is often considered to be a diffusive process. Here, we demonstrate a mechanism for the penetration of thin films and other nanoscopic barriers that is different from simple diffusion. Silver clusters that are soft-landed onto a monolayer of C 60 supported by gold sink through the monolayer in a matter of hours. However, the clusters are stable when landed onto two monolayers of C 60 supported on gold, or on one monolayer of C 60 supported on graphite. With backing from atomistic calculations, these results demonstrate that a metallic substrate exerts attractive forces on metallic nanoparticles that are separated from the substrate by a single monolayer. © 2010 Macmillan Publishers Limited. All rights reserved.
    view abstractdoi: 10.1038/nnano.2010.45
  • 2010 • 15 Brazing of titanium to steel with different filler metals: Analysis and comparison
    Elrefaey, A. and Tillmann, W.
    Journal of Materials Science 45 4332-4338 (2010)
    Evaluations of vacuum brazed commercially pure titanium and low-carbon steel joints using one copper-based alloy (Cu-12Mn-2Ni) and two silver-based braze alloys (Ag-34Cu-2Ti, Ag-27.25Cu-12.5In-1.25Ti) have been studied. Both the interfacial microstructures and mechanical properties of brazed joints were investigated to evaluate the joint quality. The optical and scanning electron microscopic results showed that all the filler metals interact metallurgically with steel and titanium, forming different kinds of intermetallic compounds (IMC) such as CuTi, Cu2Ti, Cu4Ti3, and FeTi. The presence of IMC (interfacial reaction layers) at the interfacial regions strongly affects the shear strength of the joints. Furthermore, it was found that the shear strength of brazed joints and the fracture path strongly depend on the thickness of the IMC. The maximum shear strength of the joints was 113 MPa for the specimen brazed at 750 °C using an Ag-27.25Cu-12.5In-1.25Ti filler alloy. © 2010 Springer Science+Business Media, LLC.
    view abstractdoi: 10.1007/s10853-010-4357-z
  • 2010 • 14 Formation, binding, and stability of O-Ag-CO2-Ag-O compounds on Ag(100) investigated by low temperature scanning tunneling microscopy and manipulation
    Hsieh, M.-F. and Li, H.-D. and Lin, D.-S. and Morgenstern, K.
    Journal of Physical Chemistry C 114 14173-14179 (2010)
    The understanding of reaction intermediates in heterogeneous catalysis has important implications for the design of novel catalysts. We investigate the adsorption of CO2 on oxygen precovered Ag(100) at low temperature (17 K) by scanning tunneling microscopy and inelastic electron tunneling manipulation at 5 K. On the terraces, the adsorption leads to O-Ag-CO 2-Ag-O compounds with reduced binding of the oxygen to the surface as compared to the separately adsorbed molecules. The compound can be either dissociated into a bistable O-Ag-CO2 compound at 1.6 V, dissociated into its constituents at 2.2 V, or reacted at 6.5 V into a species, which we tentatively attribute to CO3. The thus obtained carbon trioxide or carbonate is an intriguing reaction intermediate, because it is not stable in the gas phase. Our detailed study of coadsorbed species outlines a possibility to investigate precursors of reactions that involve the substrate atoms. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/jp104170b
  • 2010 • 13 Toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions
    Kittler, S. and Greulich, C. and Diendorf, J. and Köller, M. and Epple, M.
    Chemistry of Materials 22 4548-4554 (2010)
    The dissolution of citrate-stabilized and poly(vinylpyrrolidone)-stabilized silver nanoparticles in water was studied by dialysis for up to 125 days at 5, 25, and 37 °C. The particles slowly dissolve into ions on a time scale of several days. However, in all cases, a limiting value of the released silver was observed, i.e., the particles did not completely dissolve. In some cases, the nanoparticles released up to 90% of their weight. Formal kinetic data were computed. Rate and degree of dissolution depended on the functionalization as well as on the storage temperature. The release of silver led to a considerably increased toxicity of silver nanoparticles which had been stored in dispersion for several weeks toward human mesenchymal stem cells due to the increased concentration of silver ions. Consequently, "aged" (i.e., immersed) silver nanoparticles are much more toxic to cells than freshly prepared silver nanoparticles. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/cm100023p
  • 2010 • 12 The influence of proteins on the dispersability and cell-biological activity of silver nanoparticles
    Kittler, S. and Greulich, C. and Gebauer, J.S. and Diendorf, J. and Treuel, L. and Ruiz, L. and Gonzalez-Calbet, J.M. and Vallet-Regi, M. and Zellner, R. and Köller, M. and Epple, M.
    Journal of Materials Chemistry 20 512-518 (2010)
    Spherical silver nanoparticles with a diameter of 50 ± 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI-BSA mixture within a few hours, the particles remained well dispersed in RPMI-FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI-BSA and RPMI-FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins. © The Royal Society of Chemistry 2010.
    view abstractdoi: 10.1039/b914875b
  • 2010 • 11 Electrocrystallisation of metallic films under the influence of an external homogeneous magnetic field - Early stages of the layer growth
    Koza, J.A. and Mogi, I. and Tschulik, K. and Uhlemann, M. and Mickel, C. and Gebert, A. and Schultz, L.
    Electrochimica Acta 55 6533-6541 (2010)
    The effects of a uniform magnetic field on the early stages of Ag, Fe and CoFe alloys electrocrystallisation have been investigated. It was found for Fe and CoFe alloys, irrespective of the applied parameters, that early stages of the layer growth can be characterised by a nucleation and 3D diffusion controlled growth. The influence of the deposition parameters on the nucleation behaviour was studied on the basis of the Sharifker-Mostany (SM) model. A modification to the existing model has been proposed in order to model alloy systems. It is reported that a magnetic field superposed parallel to the electrode surface has a significant influence on the early stages of Fe and CoFe alloys growth. The growth of the nuclei is enhanced by the Lorentz-force-driven convection, while the nucleation processes remain unaffected. The hydrodynamic origin of these phenomena is confirmed by independent rotating disk electrode (RDE) investigations. Moreover, the proposed mechanism of a magnetic field influence on the 3D diffusion controlled growth is supported by a microscopic investigation of Ag deposits. It was found that Ag deposits obtained without a magnetic field superposition are characterised by a relatively large number of small 3D growth centres, whereas the deposits obtained in a field show fewer 3D centres but their size is greatly increased. © 2010 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.electacta.2010.06.026
  • 2010 • 10 From glycerol to allyl alcohol: Iron oxide catalyzed dehydration and consecutive hydrogen transfer
    Liu, Y. and Tüysüz, H. and Jia, C.-J. and Schwickardi, M. and Rinaldi, R. and Lu, A.-H. and Schmidt, W. and Schüth, F.
    Chemical Communications 46 1238-1240 (2010)
    Using iron oxide as catalyst, glycerol can be converted to allyl alcohol through a dehydration and consecutive hydrogen transfer. © 2010 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/b921648k
  • 2010 • 9 Synthesis and characterization of ag- or sb-doped zno nanorods by a facile hydrothermal route
    Lupan, O. and Chow, L. and Ono, L.K. and Cuenya, B.R. and Chai, G. and Khallaf, H. and Park, S. and Schulte, A.
    Journal of Physical Chemistry C 114 12401-12408 (2010)
    ZnO nanorods doped with Ag and Sb have been synthesized by a facile hydrothermal technique. Crystal quality, morphology, chemical/electronic composition, local structure, and vibrational mode properties are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and micro-Raman spectroscopy. Evidence of dopant incorporation is demonstrated in the XPS measurements of both Sb-doped and Ag-doped ZnO nanorods. From XRD data, it was found that the doped ZnO nanorods have a lower degree of crystallinity. The lattice constants of doped ZnO nanorods were slightly larger than that of the pure samples. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/jp910263n
  • 2010 • 8 Silver containing sol-gel coatings on polyamide fabrics as antimicrobial finish-description of a technical application process for wash permanent antimicrobial effect
    Mahltig, B. and Textor, T.
    Fibers and Polymers 11 1152-1158 (2010)
    This paper reports on an antimicrobial finishing for polyamide with high washfastness. As antimicrobial agent modified silica sols containing silver components are used as coating agent and are applied to the polyamide fabric by using a semi-industrial procedure. The antimicrobial properties of coated polyamide fabrics are determined against the bacteria E. coli. Significant antimicrobial effects are observed even after 40 washing cycles. The amount of silver on the polyamide fabrics was measured by using ICP-OES. Besides this, samples are investigated by means of UV/Vis-spectroscopy and scanning electron microscopy. Furthermore textile properties as, e. g., air permeability and mechanical properties were measured. Due to high antimicrobial effect and the strong washfastness of this finishing, this reported method could be of high interest for industrial production processes. © 2010 The Korean Fiber Society and Springer Netherlands.
    view abstractdoi: 10.1007/s12221-010-1152-z
  • 2010 • 7 Pt-Ag catalysts as cathode material for oxygen-depolarized electrodes in hydrochloric acid electrolysis
    Maljusch, A. and Nagaiah, T.C. and Schwamborn, S. and Bron, M. and Schuhmann, W.
    Analytical Chemistry 82 1890-1896 (2010)
    Pt-Ag nanoparticles were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and tested using cyclic voltammetry and scanning electrochemical microscopy (SECM) with respect to their possible use as catalyst material for oxygen reduction in 400 mM HCl solution. For comparison, a Pt catalyst was investigated under similar conditions. The redox competition mode of scanning electrochemical microscopy (RC-SECM) was adapted to the specific conditions caused by the presence of Cl ions and used to visualize the local catalytic activity of the Pt-Ag deposits. Similarly prepared Pt deposits were shown to dissolve underneath the SECM tip. Pt-Ag composites showed improved long-term stability toward oxygen reduction as compared with Pt even under multiple switching off to open-circuit potential in 400 mM HCl. © 2010 American Chemical Society.
    view abstractdoi: 10.1021/ac902620g
  • 2010 • 6 The influence of the surface state onto the distance distribution of single molecules and small molecular clusters
    Mehlhorn, M. and Simic-Milosevic, V. and Jaksch, S. and Scheier, P. and Morgenstern, K.
    Surface Science 604 1698-1704 (2010)
    We investigate the distance distribution of two anorganic molecules (CO, H2O), one organic radical (parabenzyne), and one strongly dipolar molecule (ortho-dinitrobenzene) on the (111) faces of copper and silver. Above the onset of diffusion, their distribution is influenced by the surface state and oscillates. While CO, H2O, and para-benzyne show the expected oscillation period of ≈λF / 2, ortho-dinitrobenzene oscillates with λF / 4. The position of the first maximum in these oscillations is consistent with a perfect scatterer for the anorganic molecules, but inconsistent for the radical and the dipolar molecule. This observation is utilized to explain the double periodicity observed in the distance distribution of ortho-dinitrobenzene. © 2010 Elsevier B.V. All rights reserved. All rights reserved.
    view abstractdoi: 10.1016/j.susc.2010.06.018
  • 2010 • 5 Influence of beam intensity profile on the aerodynamic particle size distributions generated by femtosecond laser ablation
    Menéndez-Manjn, A. and Barcikowski, S. and Shafeev, G.A. and Mazhukin, V.I. and Chichkov, B.N.
    Laser and Particle Beams 28 45-52 (2010)
    The dependence of nanoparticle size distributions on laser intensity profile was determined during infrared femtosecond laser ablation of silver targets in air. Laser parameters were adjusted to ablate at the same peak fluence with spatially homogeneous (flat-top) and inhomogeneous (Gaussian) intensity distributions formed by diffractive optical elements. Aerodynamic particle size was measured online by an electric low-pressure cascade impactor. Narrower size distributions were detected for the flat-top intensity profile in the fluence range from 0.6 to 4.4J/cm2, while the Gaussian beam produced broad and bimodal distributions. The aerodynamic number frequency of the primary nanoparticulate fraction (40nm) was equal to the number frequency of the submicron agglomerate fraction (200nm) at laser fluence of 1J/cm 2. The Feret diameter of primary particles was 80nm. Geometrical interpretation of the irradiated spots at the corresponding laser fluence regimes explains the formation of bimodal (submicron and nanoparticulate) size distribution in the case of Gaussian beams. The bimodality is attributed to different thermalization pathways during laser ablation. Copyright © 2010 Cambridge University Press.
    view abstractdoi: 10.1017/S0263034609990553
  • 2010 • 4 Silver induced faceting of Si(112)
    Nabbefeld, T. and Wiethoff, C. and Meyer zu Heringdorf, F.-J. and Horn-Von Hoegen, M.
    Applied Physics Letters 97 (2010)
    Si nanowires grown in ultrahigh vacuum by metal-catalyzed vapor-liquid-solid epitaxy are known to exhibit sidewalls with {112}-type orientation. For some metals the sidewalls show pronounced faceting. Ag induced faceting on Si(112) surfaces was studied in situ by spot-profile-analyzing low energy electron diffraction and ex situ atomic force microscopy. The (112) surface decomposes into (115)- and (111)- (√3×√3) -facets, both of which are Ag terminated. The width of the facets is kinetically limited and varies between 6 nm at T<550 °C and 30 nm at T=690 °C. © 2010 American Institute of Physics.
    view abstractdoi: 10.1063/1.3464555
  • 2010 • 3 Isomerization of an azobenzene derivative on a thin insulating layer by inelastically tunneling electrons
    Safiei, A. and Henzl, J. and Morgenstern, K.
    Physical Review Letters 104 (2010)
    Scanning tunneling microscopy is used to investigate isomerization of amino-nitro-azobenzene on a thin NaCl layer on Ag(111) by inelastically tunneling electrons. A reversible isomerization between a planar trans and a three-dimensional cis form with two different thresholds is demonstrated. The isomerization characteristics are rationalized in terms of binding of the multipolar molecule to the ionic layer. This study shows the feasibility of a bistable single molecule switch on an insulator. © 2010 The American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.104.216102
  • 2010 • 2 Anisotropy of Ag diffusion on vicinal Si surfaces
    Sindermann, S. and Wall, D. and Roos, K.R. and Horn-Von Hoegen, M. and Meyer zu Heringdorf, F.-J.
    e-Journal of Surface Science and Nanotechnology 8 372-376 (2010)
    Photoemission electron microscopy (PEEM) is used to study Ag surface diffusion on vicinal Si surfaces. The diffusion field is represented by Iso-Coverage Zones around Ag islands during desorption. By analyzing the shape and radius of the Iso-Coverage Zone we can determine diffusion parameters. For anisotropic diffusion the zone has an elliptical shape and the aspect ratio gives a measure for the anisotropy. Using this technique, we study the degree of anisotropy of Ag diffusion on vicinal Si(001) and Si(111). With increasing miscut angles, starting from Si(001) as well as from Si(111), we find a gradually increasing anisotropy, caused by the higher step density. On higher index surfaces, like Si(119), Si(115) and Si(113), we find isotropic diffusion for surfaces with comparable dimer and (double) step structure as on Si(001)-4°, where diffusion is strongly anisotropic. © 2010 The Surface Science Society of Japan.
    view abstractdoi: 10.1380/ejssnt.2010.372
  • 2010 • 1 Dissociation of oxygen on Ag(100) induced by inelastic electron tunneling
    Sprodowski, C. and Mehlhorn, M. and Morgenstern, K.
    Journal of Physics Condensed Matter 22 (2010)
    Scanning tunneling microscopy (STM) is used to study the dissociation of molecular oxygen on Ag(100) induced by inelastic electron tunneling (IET) at 5 K. This dissociation is possible above 3.3 V with a yield of (3.63 ± 0.47) × 10-9 per electron. Dissociation leads to three different types of hot atom motion: lateral motion, a cannon ball mechanism, and abstractive dissociation. Analysis of the I -t characteristics during dissociation suggests that the dissociation is proceeded by an adsorption site change. © 2010 IOP Publishing Ltd.
    view abstractdoi: 10.1088/0953-8984/22/26/264005