Transparent transfer-free multilayer graphene microelectrodes enable high quality recordings in brain slices

Resolving the underlying mechanisms of complex brain functions and associated disorders remains a major challenge in neuroscience, largely due to the difficulty in mapping large-scale neural network dynamics with high temporal and spatial resolution. Multimodal neural platforms that integrate optical and electrical modalities offer a promising approach that surpasses resolution limits. Over the last decade, transparent graphene microelectrodes have been proposed as highly suitable multimodal neural interfaces. However, their fabrication commonly relies on the manual transfer process of pre-grown graphene sheets which introduces reliability and scalability issues. In this study, multilayer graphene microelectrode arrays (MEAs) with electrode sizes as small as 10-50 µm in diameter, are fabricated using a transfer-free process on a transparent substrate for in vitro multimodal platforms. Through acute experiments using cerebellar brain slices, their ability to detect spontaneous extracellular spiking activity from neural cells, with a high signal-to-noise ratio up to 30-40 dB, is demonstrated. The recorded signal quality is found to be more limited by the electrode-tissue coupling than the MEA technology itself. Overall, this study shows the potential of transfer-free multilayer graphene MEAs to interface with neural tissue, which paves the way to advance neuroscientific research through the next-generation of multimodal neural interfaces.