Close-Packed PEDOT:PSS-Coated Graphene Microelectrodes for High-Resolution Interrogation of Neural Activity

Graphene microelectrode arrays (MEAs) have emerged as a viable neurointerfacing tool for their combined benefits in mechanical, electrical, and optical properties. To evaluate their promise for high-resolution neurointerfacing applications, here we presented a 28- $\mu \text{m}$ pitched, poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-coated graphene MEA that can achieve one order higher spatial resolution than previous graphene MEAs in both neurostimulation and optogenetic electrophysiology. The electroplated PEDOT:PSS layer improved the impedance and the charge-injection capacity of the graphene electrodes by 40–60 times (sub-100 $\text{k}\Omega $ , >1.31 mC/cm2 and maintained low light-induced artifacts among them (sub-3 $\mu$ V). As a result, our MEA was able to stimulate neuronal ensemble with single electrodes and record optogenetically evoked neural spikes with high signal-to-noise ratios. These results shed light on the possible use of PEDOT:PSS-coated graphene MEAs toward high-resolution interrogation of neural activity.