PEDOT electrode coating

PEDOT (poly(3,4-ethylenedioxythiophene), usually doped with PSS or another counter-ion) is a conducting polymer coating electrodeposited onto neural electrodes to dramatically lower their impedance and raise their charge storage and injection capacity. As a mixed ionic-electronic conductor, PEDOT conducts electrons in the polymer backbone and ions through its porous, hydrated volume, so charge is exchanged throughout a three-dimensional film rather than only at a flat metal surface; this volumetric, largely capacitive / pseudocapacitive charge transfer gives order-of-magnitude reductions in 1 kHz impedance and increases charge injection capacity to several mC/cm^2.

These properties make PEDOT attractive for miniaturized high-density arrays, where small contacts would otherwise be too noisy to record well or too limited to stimulate. The main concern is chronic mechanical stability: PEDOT films can delaminate or crack, and their long-term durability under repeated stimulation and in the biological environment remains an active reliability question, so composites, adhesion layers, and alternative dopants are areas of ongoing engineering.