Electrochemical and Nanostructural Characterization of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) Films as Coatings for Neural Electrodes

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT), a well-characterized conducting polymer, has been applied for coating metal neural electrodes to improve their stimulating or recording performance. The coated electrodes possess advantages in better neuron attachment, lower impedance, and larger capacitance compared to the bare metal substrate due to the biocompatibility and porous surface of the polymer. However, the PEDOT-coated electrodes have frequently reported issues associated with mechanical instability, such as cracking and delamination. Solving this problem is crucial for stimulating electrodes, whereas a massive film is unnecessary for recording purposes. Moreover, the thickness control for the latter has rarely been investigated. In this work, we systematically studied and characterized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with cyclic voltammetry and atomic force microscopy (AFM) to evaluate the electropolymerization of PEDOT:PSS from the basis and analyze the surface morphology for a range of deposition times. The polymerization potential was obtained, and the deposition charge density was optimized for recording neural electrodes. In addition, high-resolution AFM height and phase images reveal the heterogeneity of the polymer surface. The modified electrode was also tested for its electrochemical performance in a small potential window with both a standard electrochemical cell setup and stainless steel microscrews. The results showed that despite a shift of potential (0.42 V) due to the change of setup, the electrode functions well in the capacitive region without triggering redox reactions.