| Summary: | A graphene-based capacitive NO<sub>2</sub> sensing device was developed by utilizing the quantum capacitance effect. We have used a graphene field-effect transistor (G-FET) device whose geometrical capacitance is enhanced by incorporating an aluminum back-gate electrode with a naturally oxidized aluminum surface as an insulating layer. When the graphene, the top-side of the device, is exposed to NO<sub>2</sub>, the quantum capacitance of graphene and, thus, the measured capacitance of the device, changed in accordance with NO<sub>2</sub> concentrations ranging from 1–100 parts per million (ppm). The operational principle of the proposed system is also explained with the changes in gate voltage-dependent capacitance of the G-FET exposed to various concentrations of NO<sub>2</sub>. Further analyses regarding carrier density changes and potential variances under various concentrations of NO<sub>2</sub> are also presented to strengthen the argument. The results demonstrate the feasibility of capacitive NO<sub>2</sub> sensing using graphene and the operational principle of capacitive NO<sub>2</sub> sensing.
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