Application of nanoelectrodes in recording biopotentials

Previous attempts at directly recording sympathetic activity using wire electrodes without significant filtering have yielded poor signal-to-noise ratio. This is because the amplitude of the signal from a sympathetic nerve is typically -35 to +35 μV and the electrode noise is on average 10 μV for an ideal electrode resistance between 100 kΩ and 10 MΩ at 37°C for a bandwith of 1 kHz. We hypothesized that if we fabricated an electrode with increased nervous tissue surface contact that was sharp enough to penetrate the epineurium without damaging sympathetic neurons we would improve our signal-to-noise ratio and therefore be able to record high fidelity sympathetic activity. We built an array of nano-sized rods on a silicon substrate using a combination of micro- and nanofabrication techniques. Afterwards, we patterned and deposited aluminum on the surface of our processed silicon substrate in order to form a bipolar biopotential electrode with a three-dimensional surface. At this time our fabrication technique did not include a passivation layer. This configuration allowed us to examine the performance of a bipolar electrode without much of the effects related to the parasitic capacitance. The signal-to-noise ratio of our recordings in wet media were similar for both the wire electrde and the bipolar nanoelectrode array. Finally, we were able to record stimulated nerve activity when the bipolar nanoelectrode array was placed on the cardiac sympathetic nerve of an anesthetized animal.