Transparent Graphene/PEDOT:PSS Microelectrodes for Electro- and Optophysiology

Conventional opaque electrodes in microelectrode array (MEA) technology obstruct the view of cells in their immediate vicinity (e.g., approximate to 50 mu m) from which the strongest extracellular action potentials are recorded. This limitation has been overcome by transparent graphene electrodes which allow for optical access essential for novel applications such as optogenetics and calcium imaging. Downscaling, necessary for high resolution single-unit electrophysiological recordings, has been a significant challenge due to inferior electrochemical impedance and correspondingly lower signal-to-noise ratio. Here, the combination of graphene with the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a transparent microelectrode material for in vitro MEAs is presented and their application with optical imaging and electrophysiology is demonstrated. Optimal graphene/PEDOT:PSS microelectrodes display transparencies of 84% over the visible spectrum and impedance magnitude of (166 +/- 13) k Omega at 1 kHz. The balance of transparency and 1 kHz impedance can be tuned from approximate to 90% and 700 k Omega to 50% and 42 k Omega.