Center for Nanotechnology ech

Bad Münster am Stein-Ebernburg, Germany

Center for Nanotechnology ech

Bad Münster am Stein-Ebernburg, Germany
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Hua Y.,Max Planck Institute for Biophysical Chemistry | Hua Y.,University of Munster | Sinha R.,Max Planck Institute for Biophysical Chemistry | Sinha R.,University of Munster | And 12 more authors.
Nature Neuroscience | Year: 2011

Although clathrin-mediated endocytosis is thought to be the predominant mechanism of synaptic vesicle recycling, it seems to be too slow for fast recycling. Therefore, it was suggested that a presorted and preassembled pool of synaptic vesicle proteins on the presynaptic membrane might support a first wave of fast clathrin-mediated endocytosis. In this study we monitored the temporal dynamics of such a 'readily retrievable pool' of synaptic vesicle proteins in rat hippocampal neurons using a new type of probe. By applying cypHer5E, a new cyanine dye-"based pH-sensitive exogenous marker, coupled to antibodies to luminal domains of synaptic vesicle proteins, we could reliably monitor synaptic vesicle recycling and demonstrate the preferential recruitment of a surface pool of synaptic vesicle proteins upon stimulated endocytosis. By using fluorescence nanoscopy of surface-labeled synaptotagmin 1, we could resolve the spatial distribution of the surface pool at the periactive zone in hippocampal boutons, which represent putative sites of endocytosis. © 2011 Nature America, Inc. All rights reserved.

Diaz Arado O.,University of Munster | Diaz Arado O.,Center for Nanotechnology ech | Monig H.,University of Munster | Monig H.,Center for Nanotechnology ech | And 9 more authors.
ACS Nano | Year: 2013

We present [3 + 2] cycloaddition reactions between azides and alkynes on a Au(111) surface at room temperature and under ultrahigh vacuum conditions. High-resolution scanning tunneling microscopy images reveal that these on-surface cycloadditions occur highly regioselectively to form the corresponding 1,4-triazoles. Density functional theory simulations confirm that the reactions can occur at room temperature, where the Au(111) surface does not participate as a catalytic agent in alkyne C-H activation but acts solely as a two-dimensional constraint for the positioning of the two reaction partners. The on-surface azide-alkyne cycloaddition offers great potential toward the development and fabrication of functional organic nanomaterials on surfaces. © 2013 American Chemical Society.

Falter J.,Center for Nanotechnology ech | Langewisch G.,Center for Nanotechnology ech | Holscher H.,Karlsruhe Institute of Technology | Fuchs H.,Center for Nanotechnology ech | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Direct comparison of tip-sample forces obtained by dynamic force spectroscopy experiments with theoretical simulations is extremely difficult, since the precise tip shape and chemical identity of the apex atoms of the force sensing tip remain unknown in most experiments. Here, we present force curves measured with a tungsten tip on a Ag(111) surface obtained in a low-temperature atomic force microscope using tips that were analyzed by field ion microscopy down to atomic levels. The resulting van der Waals and electrostatic forces were found to be in quantitative agreement with analytical models, if the tip shape parameters from the field ion microscopy analysis were used. Furthermore, our analysis shows an additional long-range force interaction at tip-sample distances above 1.3 nm. We suggest that this unexpected force is related to patch charges arising from the inhomogeneous work function distribution on the surface of highly faceted sharp tips. © 2013 American Physical Society.

Schmutz J.-E.,Center for Nanotechnology ech | Schmutz J.-E.,University of Munster | Fuchs H.,Center for Nanotechnology ech | Fuchs H.,University of Munster | Holscher H.,Karlsruhe Institute of Technology
Wear | Year: 2010

We introduce a technique for measuring wear on the nano-scale by combining friction force and dynamic force microscopy. By measuring the resonance frequency of the cantilever after scratching over a sample surface we are able to detect the increase or decrease of the tip's worn mass down to some picograms. Applying a recently developed technique to attach a small sphere to the upper end of the cantilever's tip we are able to measure the nano-wear of several material combinations with this approach. © 2009 Elsevier B.V. All rights reserved.

Feldmann M.,Justus Liebig University | Dietzel D.,Justus Liebig University | Fuchs H.,Center for Nanotechnology ech | Fuchs H.,University of Munster | And 2 more authors.
Physical Review Letters | Year: 2014

One of the oldest concepts in tribology is stick-slip dynamics, where a disruptive sequence of stick and slip phases determine the overall resistance in sliding friction. While the mechanical energy dissipates in the sudden slip phase, the stick phase has been shown to be characterized by contact strengthening mechanisms, also termed contact aging. We present experiments of sliding nanoparticles, where friction is measured as a function of sliding velocity and interface temperature. The resulting complex interdependence is in good agreement with Monte Carlo simulations, in which the energy barrier for contact breaking increases logarithmically with time, at a rate governed by thermal activation. © 2014 American Physical Society.

Hentschel C.,University of Munster | Hentschel C.,Center for Nanotechnology ech | Wagner H.,University of Munster | Smiatek J.,University of Munster | And 5 more authors.
Langmuir | Year: 2013

Herein we present a study on nonspecific binding of proteins at highly dense packed hydrophobic polystyrene brushes. In this context, an atomic force microscopy tip was functionalized with concanavalin A to perform single-molecule force spectroscopy measurements on polystyrene brushes with thicknesses of 10 and 60 nm, respectively. Polystyrene brushes with thickness of 10 nm show an almost two times stronger protein adsorption than brushes with a thickness of 60 nm: 72 pN for the thinner and 38 pN for the thicker layer, which is in qualitative agreement with protein adsorption studies conducted macroscopically by fluorescence microscopy. © 2013 American Chemical Society.

Lee Y.,University of Munster | Jung G.-E.,Park Systems Corporation KANC | Cho S.J.,Park Systems Corporation KANC | Cho S.J.,University of Suwon | And 4 more authors.
Nanoscale | Year: 2013

Halloysite nanotube (HNT)-based supramolecular complexes are synthesized and evaluated with respect to their cytotoxicity and effects on cellular structures. As HNTs are water-insoluble, DNA is applied for wrapping the surface of HNTs to enhance their water-dispersibility. To investigate the potential of DNA-wrapped HNTs (HD) as a promising drug delivery carrier, doxorubicin (DOX) is introduced as a model anticancer agent and loaded onto HD. The DOX-loaded, DNA-wrapped HNTs (HDD) show sustained DOX release over two weeks without initial burst of DOX indicating delayed DOX release inside cells. In addition, effects of DNA-wrapped HNTs (HD) or HDD on the cytoskeleton organization of A549 cells are studied by visualizing the distribution of F-actin filaments using confocal laser scanning microscopy, and cellular morphological changes are observed by scanning electron microscopy and scanning ion conductance microscopy. © 2013 The Royal Society of Chemistry.

Jansen L.,University of Munster | Jansen L.,Center for Nanotechnology ech | Jansen L.,Robert Bosch GmbH | Lantz M.A.,IBM | And 3 more authors.
Langmuir | Year: 2014

Sliding friction between a silicon tip and a polymer bilayer system consisting of a polystyrene (PS) film covered with a few-nanometers-thick capping layer of hard plasma polymer is studied using friction force microscopy. The system was chosen to enable subsurface dissipation channels to be distinguished from surface friction. Frictional energy dissipation in the underlayer can be identified through the kinetics of the polymer relaxation modes that we measured using nanoscale friction experiments as a function of sample temperature, scanning velocity, and applied load. We found a strong nonlinear increase in friction as a function of applied load around the glass-transition temperature of the PS underlayer. This behavior is a clear signature of frictional dissipation occurring in the volume of the polystyrene layer, well below the surface of the sample. The time-temperature kinetics associated with frictional energy dissipation into the PS was found to be in agreement with the known material properties of PS. Moreover, the data was found to support the hypothesis that the observed friction can be understood as the sum of friction resulting from the relaxation process in the polymer underlayer induced by stress due to the sliding of the tip and a second term associated with dissipation due to sliding friction on the capping layer. © 2014 American Chemical Society.

Fernaindez-Hernaindez J.M.,Physikalisches Institute | Fernaindez-Hernaindez J.M.,Center for Nanotechnology ech | Yang C.-H.,Physikalisches Institute | Yang C.-H.,Center for Nanotechnology ech | And 9 more authors.
Journal of the American Chemical Society | Year: 2011

Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)2Cl]2, and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)2(L^L)]+ (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz) 2Cl]2, are synthesized depending on the reaction conditions. At 80 °, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz) 2Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz) 2(dmbpy)]+ (dmbpy = 4,4′-dimethyl-2,2′- bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)2(dmbpy)]+, with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data. © 2011 American Chemical Society.

Sondhauss J.,Center for Nanotechnology ech | Sondhauss J.,University of Munster | Fuchs H.,Center for Nanotechnology ech | Fuchs H.,University of Munster | Schirmeisen A.,Justus Liebig University
Tribology Letters | Year: 2011

Friction between titanium spheres and an artificially structured silicon surface was measured with a friction force microscope. Two spheres with radii of 2.3 μm and 7.9 μm were firmly glued to the tip of the microscope cantilever. A periodic stripe pattern with a groove depth of 26 nm and systematically increasing groove width from 500 nm to 3500 nm was fabricated from a silicon wafer with a focused ion beam. The sphere substrate friction coefficient shows a strong enhancement at a certain groove periodicity, which is related to geometrical interlocking of the two surfaces. This shows that careful modification of the surface roughness can help to control the tribological behavior of mesoscale contacts. © 2011 Springer Science+Business Media, LLC.

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