Electrochemical characteristics of ultramicro-dimensioned SIROF electrodes for neural stimulation and recording.

Objective. With ever increasing applications of neural recording and stimulation, the necessity for developing neural interfaces with higher selectivity and lower invasiveness is inevitable. Reducing the electrode size is one approach to achieving such goals. In this study, we investigated the effect of electrode geometric surface area (GSA), from 20 mu m(2) to 1960 mu m(2), on the electrochemical impedance and charge-injection properties of sputtered iridium oxide (SIROF) coated electrodes in response to current-pulsing typical of neural stimulation. These data were used to assess the electrochemical properties of ultra-small SIROF electrodes (GSA < 200 mu m(2)) for stimulation and recording applications. Approach. SIROF charge storage capacities (CSC), impedance, and charge-injection characteristics during current-pulsing of planar, circular electrodes were evaluated in an inorganic model of interstitial fluid (model-ISF). Main results. SIROF electrodes as small as 20 mu m(2) could provide 1.3 nC/phase (200 mu s pulse width, 0.6 V versus Ag|AgCl interpulse bias) of charge during current pulsing. The 1 kHz impedance of all electrodes used in this study were below 1 M ohm, which is suitable for neural recording. Significance. Ultra-small SIROF electrodes are capable of charge injection in buffered saline at levels above some reported thresholds for neural stimulation with microelectrodes.