Correlation of impedance and effective electrode area of dextran sulfate doped PEDOT modified electrodes

The impedance of electrodes at 1 kHz is typically reported to assess the signal-to-noise ratio of neural recording electrodes. The impedance response of platinum electrodes modified by poly-3,4-ethylenedioxythiophene doped with dextran sulfate has been examined. The modified electrodes have lower impedance at low and intermediate frequencies compared to unmodified electrodes. The impedance and phase angle at low frequencies is strongly correlated with the electrode area. The geometric and linear diffusion charge densities of the modified electrodes are also dependent on the electrode area and impedance at low frequencies. A 3 time constant equivalent circuit provided a better fit to the impedance than a 2 time constant model. The decrease in impedance at low frequencies indicates PEDOT-DS will be suitable for reducing the thermal noise and increasing the signal-to-noise ratio for neural recording electrodes.