Transfer-Free Fabrication and Characterisation of Transparent Multilayer CVD Graphene MEAs for In-Vitro Optogenetic Applications

This study explores the application of a novel transfer-free method for the synthesis of multilayer Chemical Vapour Deposition (CVD) graphene directly on transparent sub-strates, specifically to create transparent Microelectrode Arrays (MEAs) for optogenetic studies. Traditional methods typically involve a graphene transfer step that can compromise the material's integrity and electrical properties. By eliminating this step, our approach simplifies the fabrication process. The developed MEAs were characterised by Raman spectroscopy, op-tical transmittance, and electrochemical impedance spectroscopy. We also assessed the stability and recording capabilities of the fabricated MEAs, alongside a comparative assessment with a commercial MEA. Turbostratic graphene grown directly on quartz and sapphire was successfully achieved. Our transfer-free MEAs exhibit promising signal detection capabilities, despite a relatively high baseline noise of
$\sim 23\mu V$
. and a significantly large impedance at 1 kHz (3.2 to 9.89
${M}\Omega)$
surpassing values in other studies. The devices exhibited low stability after exposure to liquid media during the soaking and ageing tests, causing large variations in the electrochemical measurements post-exposure. This was due to the permeability of the encapsulation layer and the biodegradability of the molybdenum structures, which led to significant structural and chemical changes in the devices. While further work is required to prevent the failure mechanisms of the device, this study demonstrates the feasibility of transparent MEA fabrication by means of a transfer-free approach directly on quartz substrates.