Thin-film silica sol-gel coatings for neural microelectrodes

The reactive tissue response of the brain to chronically implanted materials remains a formidable obstacle to stable recording from implanted microelectrodes. One approach to mitigate this response is to apply a bioactive coating in the form of an ultra-porous silica sol-gel, which can be engineered to improve biocompatibility and to enable local drug delivery. The first step in establishing the feasibility of such a coating is to investigate the effects of the coating on electrode properties. In this paper, we describe a method to apply a thin-film silica sol-gel coating to silicon-based microelectrodes, and discuss the resultant changes in the electrode properties. Fluorescently labeled coatings were used to confirm coating adherence to the electrode. Cyclic voltammetry and impedance spectroscopy were used to evaluate electrical property changes. The silica sol-gel was found to successfully adhere to the electrodes as a thin coating. The voltammograms revealed a slight increase in charge carrying capacity of the electrodes following coating. Impedance spectrograms showed a mild increase in impedance at high frequencies but a more pronounced decrease in impedance at mid to low frequencies. These results demonstrate the feasibility of applying silica sol-gel coatings to silicon-based microelectrodes and are encouraging for the continued investigation of their use in mitigating the reactive tissue response.