We are developing a cell-based biosensor consisting of a planar microelectrode array that allows detection of extracellular potentials and their modulation in the presence of toxins or other active agents. To improve cell–electrode coupling, the microelectrodes were electroplated with platinum black. We report on the use of imaging x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), impedance measurements, and extracellular recordings to assess the effectiveness of this procedure. SEM provided highly detailed images of the shape and structure of well-formed deposits of thickness on the order of 1 μm or more. Because of its inherent high surface sensitivity, imaging XPS could reveal the presence of platinum deposits that were too thin to be detected by SEM. For typical, well-plated microelectrodes, impedance measurements showed reductions in the electrical resistance at 100 Hz from roughly 60 MΩ or more 1 MΩ. The overall electronic coupling of biopotentials to the microelectrodes was demonstrated by recordings obtained from beating rat myocytes and from rat spinal cord cells.
We report the first demonstration of vacuum field emission from an electron source fabricated from self-assembling biomolecular composite microstructures. Diacetylenic lipid DC8,9PC is used to form hollow, 0.5 μm diam, ≳50 μm long, tubelike structures that are subsequently plated with metal and formed into an aligned composite in an epoxy matrix. The composite material is thin-sectioned across the axis of alignment and then etched to expose the plated tubules. The sharp edges of the exposed metal tubules produce a very large local electric field enhancement, allowing for the vacuum field emission of significant current densities at relatively low applied macroscopic fields (≤60–80 kV/cm).
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We report on measurements of vacuum field emission from ungated field emission cathode arrays fabricated from Si-TaSi2 eutectic composite wafers. The Si-TaSi2 material is an ideal candidate for large area field emission array cathodes due to the large density of TaSi2 fibers incorporated into the Si matrix, the high melting point of the TaSi2 material, the ease with which single-crystal large diameter (2.5 cm) material can be fabricated, and the promise of integrability of the field emission array with conventional Si technology through the use of epitaxial Si layers grown on the cathode backplane.
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