Effective area and charge density of dextran sulphate doped PEDOT modified electrodes

The performance of neural electrodes over chronic periods is poor with degrading signal-to-noise ratio and low biocompatibility. Consequently, electrodes require modification to improve their performance, biostability and biocompatibility. A large variety of doped conducting polymers have been proposed for optimising neural electrodes, but to date, none have achieved the required biostability and biocompatibility necessary for human application. Dextran sulfate is used as an antithrombotic and may be of use in improving neural electrode biocompatibility. Poly-3,4-ethylenedioxythiophene was successfully doped with dextran sulfate (PEDOT-DS) by electropolymerisation on neural electrode arrays. Deposited films increased the electrode area and displayed a rough morphology compared to uncoated electrodes. Electrode area and charge density were obtained using microscopy and reduction of Ru(NH3)63+. Deposition charge, geometrical and linear diffusion electroactive areas were strongly correlated with deposition time. The charge density calculated from the geometric area was greater on PEDOT-DS modified electrodes than unmodified and PEDOT-para-toluene sulfonate (PEDOT-pTs) modified electrodes. The charge density calculated from the linear diffusion electroactive area was smaller on PEDOT-DS modified electrodes than unmodified and PEDOT-pTs modified electrodes. The charge density of the PEDOT-DS modified electrodes was dependant on the electrode area.