Recording sympathetic nerve activity using bipolar electrodes incorporating nanoscale features

This work describes the recording of sympathetic nerve activity using a new type of electrode that controllably penetrates the epineurium thus leading to an improved signal to noise ratio (SNR). Conventional methods for autonomic nerve recording make use of wire electrodes which typically have a poor SNR. This is because the amplitude of the signal from a sympathetic nerve typically reaches an amplitude of approximately 35 muV and the electrode noise is on average 10 muV for an ideal electrode resistance between 100 kO and 10 MO at 37°C for a bandwidth of 1 kHz.10 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 higher fidelity sympathetic nerve activity.; We built an array of nano-sized needles on a silicon substrate using a conventional microfabrication technology that leads to arrays of atomically sharp structures. Afterwards, we deposited and patterned and deposited gold on the surface of our processed silicon substrate in order to form a bipolar biopotential electrode with a three-dimensional surface. This configuration allowed us to examine the performance of a bipolar electrode with decreased transfer resistance between the extracellular nerve tissue environment and the electrode surface.; The experimentally determined value of noise generated by our nanoelectrode (1.9 microvolts) was close to our predicted value of (1.42 microvolts) and almost one order of magnitude better than those of other existing microelectrode array technologies. The performance of our nanoelectrodes remained relatively unchanged after packaging the backside interconnects with silicone elastomer. During animal testing the quality of the sympathetic nerve signal was significantly improved compared with simultaneous macro-sized wire recordings. Comparative signal analysis was also concurrent with our qualitative assessment showing a SNR of 22.90 decibels for the wire electrode and a better SNR of 38.11 decibels for the bipolar nanoelectrode.