Fig. 1: Graphene-based microelectrode array for brain mapping on the cortical surface.

a Schematic illustration of the graphene-based electrode array. b Optical image of the device on the cortical surface. c Nyquist plot of 4 L-doped graphene and gold electrodes; measurements were conducted using the three-electrode method with a platinum counter electrode and Ag/AgCl reference electrode in 0.01 M phosphorus buffered saline. The surface area of the electrode is 60 × 60 μm². A graph and an image of the inset show the magnified plot of 4 L-doped graphene and gold electrodes and an equivalent circuit model of 4 L-doped graphene and gold, respectively. The results of the equivalent circuit model are noted in Table S1. d Histogram showing the impedance of 30 channels comprising the electrode array. Impedance was derived via electrochemical impedance spectroscopy (EIS) at 1 kHz. e Impedance of 4 L-doped graphene electrodes with respect to the bending radius. f Illustrations of rat auditory and somatosensory cortices. Two maps of auditory and somatosensory areas responding to auditory stimuli with various frequency tones and physical stimuli applied to each body part. g Thirty-channel (excluding the reference and ground electrodes) recording of the graphene-electrode array on the cortical surface. The colors of boxes correlate with the geographical location of the rat’s cortical surface.