▎ 摘　　要

Graphene applications in chemical sensing are based on the chemical doping of graphene. In this process, molecules adsorbed on graphene serve as charge-carrier donors or acceptors, thus changing the graphene conductivity. While the previous studies have been focused on chemical sensors with electrical detection, we theoretically investigate chemical sensing based on photonic structures covered with graphene. By considering chemical doping of graphene as a small perturbation, we show that optimal photonic structures operate at low-terahertz frequencies, with the reflectance intensity as the output signal. In order to achieve an efficient chemical sensing, photonic structures should provide the electric-field enhancement within the graphene plane. As a result, the proposed structure consists of the metallic mirror and quarter-wavelength-thick dielectric spacer with graphene on the top of it. The sensitivity is maximized when the Fermi energy in the graphene not exposed to the environment is around 30 meV. By taking the resolution for the reflectance measurement of 1%, we show that the proposed sensing structure can detect graphene doping by 150 electrons or holes per square micrometer in the dynamic range of around 3000 charge carriers.