C. Adam, F. Kanoufi, N. Sojic and M. Etienne.
Shearforce detection was applied to the controlled positioning of nanotip arrays at air/solid and liquid/solid interfaces in scanning electrochemical microscopy (SECM). The arrays were fabricated by wet chemical etching of ordered optical fiber bundles. The shearforce detection have been performed with a non-optical detection setup between 70 and 170 kHz. The hydrodynamic nature of the shearforce interaction led to approach curves with length varying from few μm to more than 80 μm, essentially controlled by the working frequency (resonance frequency), the nature of the medium (air, water, electrophoretic paint solution) and the surface state of the fiber bundle (cleaved or etched). This interface sensitive signal was applied to the positioning of the nanotip array in a 1 μm PDMS film before the electrophoretic deposition of an insulating paint. The resulting nanoprobe electrode array, displaying nanotip electrodes individually insulated, has been characterized by cyclic voltammetry and SECM feedback curves. These results are discussed versus numerical simulations. They demonstrate that, except when in vicinity of a conductive substrate that may reveal the nanotip structure, the electrochemical behavior of the nanotip array is dictated by its micrometer dimension (the fiber bundle). In turn, they confirm the potential of shearforce detection for precise control over the array positioning.
Bipolar electrochemistry is an unconventional technique that currently encounters a renewal of interest due to modern applications in the fields of analytical chemistry or materials science. The approach is particularly relevant for the preparation of asymmetric objects or surfaces such as Janus particles for example. Bipolar electrochemistry allows spatially controlled deposition of various layers from electroactive precursors, selectively at one side of a bipolar electrode. We report here the concomitant cathodic deposition of up to three different metals at the same time in a single experiment. The deposits were characterized by optical and electron microscopy imaging as well as profilometry and energy dispersive X-ray spectroscopy. As a result, the deposited layer is composed of several areas exhibiting both a composition and a thickness gradient. Such a variation directly modifies the optical and electronic properties alongside the surface and gives access to the design of composite surfaces exhibiting a visual gradient feature.
C. Hubert, C. Chomette, A. Désert, M. Sun, M. Treguer, S. Mornet, A. Perro, E. Duguet, S. Ravaine
Silica particles with a controlled number of entropic patches, i.e. dimples, are synthesized through the growth of the silica core of binary multipods that have been produced by a seeded-growth emulsion polymerization reaction. Transmission electron microscopy studies indicate that the silica surface conforms to the shape of the polystyrene (PS) nodules of the multipods while growing, allowing a good control of the final shape of the dimpled silica particles. The PS nodules are also used as protecting masks to regioselectively graft amino groups, as revealed by the adsorption of gold markers. After dissolution of the PS nodules, some polymer chains remain grafted onto the silica surface, forming organic bumps. These residues are also selectively functionalized, leading to silica particles with both entropic and enthalpic patches.
The present study focused on gap junctional intercellular communication (GJIC) as a target for biological effects of extremely low-frequency (ELF) magnetic field (MF) exposure. Fluorescence recovery after photobleaching microscopy (FRAP) was used to visualize diffusion of a fluorescent dye between NIH3T3 fibroblasts through gap junctions. The direct effect on GJIC function of a 24 h exposure to 50 Hz MF at 0.4 or 1 mT was assessed in one series of experiments and the potential synergism of MF with an inhibitor of GJIC, phorbol ester (TPA), was studied in another series by observing FRAP when NIH3T3 cells were incubated with TPA for 1 h following a 24 h exposure to MF. In contrast with other reports of ELF-MF effects on GJIC, under our experimental conditions we observed neither direct inhibition of GJIC nor synergism with TPA-induced inhibition by 50 Hz MF exposures.
V. Eßmann, D. Jambrec, A. Kuhn, W. Schuhmann
The range of potential analytes for bipolar electrochemistry can be significantly extended by modification of bipolar electrodes with enzymatic biosensing layers. In this study, we employed a Prussian blue-based glucose detection system involving electrochemical reduction of enzymatically generated hydrogen peroxide at the cathodic pole. The concentration of glucose in solution can be correlated with oxidative luminol electrochemiluminescence at the opposite anodic pole, which was recorded with a photomultiplier tube. This opens a route for novel analytical systems using glucose oxidase as an amplification element for the reporter reaction.
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