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    Combining super-resolution microcopy with neuronal network recording using magnesium fluoride thin films as cover layer for multi-electrode array technology
    (Berlin : Nature Publishing, 2019) Schmidl, Lars; Schmidl, Gabriele; Gawlik, Annett; Dellith, Jan; Hübner, Uwe; Tympel, Volker; Schmidl, Frank; Plentz, Jonathan; Geis, Christian; Haselmann, Holger
    We present an approach for fabrication of reproducible, chemically and mechanically robust functionalized layers based on MgF2 thin films on thin glass substrates. These show great advantages for use in super-resolution microscopy as well as for multi-electrode-array fabrication and are especially suited for combination of these techniques. The transparency of the coated substrates with the low refractive index material is adjustable by the layer thickness and can be increased above 92%. Due to the hydrophobic and lipophilic properties of the thin crystalline MgF2 layers, the temporal stable adhesion needed for fixation of thin tissue, e.g. cryogenic brain slices is given. This has been tested using localization-based super-resolution microscopy with currently highest spatial resolution in light microscopy. We demonstrated that direct stochastic optical reconstruction microscopy revealed in reliable imaging of structures of central synapses by use of double immunostaining of post- (homer1 and GluA2) and presynaptic (bassoon) marker structure in a 10 µm brain slice without additional fixing of the slices. Due to the proven additional electrical insulating effect of MgF2 layers, surfaces of multi-electrode-arrays were coated with this material and tested by voltage-current-measurements. MgF2 coated multi-electrode-arrays can be used as a functionalized microscope cover slip for combination with live-cell super-resolution microscopy.
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    Ultrathin niobium nanofilms on fiber optical tapers--a new route towards low-loss hybrid plasmonic modes
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A.
    Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.