▎ 摘　　要

Imaging-based molecular fingerprint detection in the mid-infrared region has emerged as a promising technique for the chemical identification of various molecules through pixelated dielectric metasurfaces. However, the integration and practical application of the device are hindered by the lack of tunability and insufficient sensitivity. In this context, a compact metasurface nanophotonic sensor consisting of graphene nanoribbon arrays is proposed and verified numerically by using a series of gate-tunable sharp localized surface plasmon resonances, which enables ultrasensitive imaging-based molecular fingerprint detection in the mid-infrared region. The graphene metasurface is excited by p-polarized light at an oblique angle and supports extremely confined surface plasmons matching nanoscale samples. Especially, the absorption signals of target molecules are significantly enhanced under the oblique incidence of light, and the absorption signatures of even 1% A/G-IgG protein bilayer physisorption can be observed in the absorbance signals calculated from the light intensity spectra. Moreover, imaging-based detection of ultra-sharp absorption signature, such as the polyethylene molecule, is also achieved using the graphene/silicon grating hybrid structure with sharper surface plasmon resonances. The gate-tunable and extremely confined graphene plasmons will provide sensitive and integrated mid-infrared spectroscopy devices.