Microporous conducting polymers on neural microelectrode arrays: II. Physical characterization

Abstract The electrochemical properties of microporous poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) films deposited on microfabricated neural electrodes were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Microporous conducting polymer films were electrochemically deposited on neural microelectrodes in galvanostatic mode from aqueous solutions containing 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) monomer with lithium perchlorate (LiClO4) as the counter ion. Impedance spectroscopy was obtained for microporous conducting polymer coated microelectrodes over a frequency range from 1 Hz to 100 kHz. Impedance spectroscopy of neural microelectrodes with microporous films of different thickness and different pore sizes was investigated in buffer solution (pH 7.0). The EIS results show that the microporous coatings decrease the impedance modulus by almost two-orders of magnitude at a frequency of 1 kHz. The EIS data were fitted to an equivalent electric circuit model. The results show that the diffusion capacitance and resistance of the films both increase with deposition charge. The significant drop in impedance magnitude and phase angle is consistent with an increase of the surface area due to the open, roughened morphology. In comparison with microporous PPy/LiClO4, microporous PEDOT/LiClO4 demonstrated much better electrochemical stability, losing only 5% of its original charge capacity after 120 cycles of CV measurement, while microporous PPy/PSS lost 30% under the same conditions.