Extended Data Fig. 1: Graphene-based ion sensitive field effect transistor (ISFET).

a) Schematic and b) optical image of exemplary graphene ISFET. The device architecture employs an insulating capping layer over the source and drain contacts, leaving only the graphene channel exposed to the liquid. This configuration suppresses parasitic electrochemical reactions at the electrodes and ensures that signal modulation originates from the graphene/liquid interface. An integrated reference electrode, fabricated on-chip and in direct contact with the analyte, applies the gate potential, forming the EDL at the graphene/liquid interface that acts as an ultra-thin, high-capacitance dielectric. In liquid-gated operation, leakage currents can occur through the electrolyte; however, the high intrinsic conductivity of graphene ensures that the channel current dominates over leakage current, yielding a superior signal-to-noise ratio (\({\rm{SNR}}\)) compared to many other nanomaterials of similar dimensions.