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Graphene has attracted great interest for integrated photonic platforms in the long‐wave infrared (LWIR) for spectroscopic and polarimetric sensing due to the capability of on‐chip integration, fast response, and broadband operation. However, graphene suffers from low photoresponsivity and thus poor sensing performance due to weak absorption. Polarization detection using graphene is hindered by its small in‐plane anisotropy. Here, nanoantenna‐mediated graphene photodetectors (NMGPDs) are proposed to enhance responsivity by tailoring the nanoantenna near‐field distribution to generate a strong photoresponse. The devices demonstrate a high responsivity of 6.3 V W−1 under zero bias at room temperature with low noise‐equivalent power of 1.6 nW Hz−1/2. Furthermore, polarization detection is enabled by artificial near‐field anisotropy enabled by double L‐shaped nanoantennas. The proposed LWIR NMGPDs achieve subtle polarization‐angle detection down to 0.05° thanks to the unusual negative polarization ratio of −1. To demonstrate the advances of LWIR NMGPDs for molecule detection, acetone is chosen as an analyte for spectroscopic sensing. The devices show a low limit of detection of 115 ppm, and fast dynamic gas sensing response of 6 s for real‐time monitoring. These results reveal the potential of the device as a multi‐functional on‐chip miniaturized optoelectronic platform for polarimetric and spectroscopic sensing toward real‐time environmental monitoring and biomedical screening.

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