A complementary impedance spectroscopy biosensing method with graphene

We present a biosensing platform based on a graphene liquid-gate field-effect transistor functionalized with a bioactive layer. The proximity of the graphene channel to the functional layer enables sensitive detection of analyte-induced changes via complex AC impedance of the graphene itself, expressed as X+iY. This approach parallels classical Electrochemical Impedance Spectroscopy (EIS), but with current flowing laterally along the graphene channel rather than through the electrolyte between EIS electrodes. We introduce a novel metric, Y/X², which at low frequencies is proportional to the effective capacitance arising from three capacitances in series: the quantum capacitance of graphene, the electrical double-layer capacitance, and the capacitance of the functional layer. This metric exhibits high sensitivity to analyte presence and demonstrates excellent baseline stability, making it well-suited for reliable biomarker detection. The technique supports biosensor miniaturization, ensures stable operation, and offers a practical route toward robust and scalable bioelectronic sensing applications.