Graphene-Enhanced\nRefreshable Metasurface Expands\nAnalytes of THz Label-Free Sensing and Achieves Picogram Limit of\nDetection

THz sensing offers unique advantages including strong\npenetrability,\nlow photon energy, and specific recognition of biomolecules and chemicals.\nHowever, current label-free THz sensors all operate below 1 THz, severely\nlimiting applications as many drugs and chemicals vibrate at higher\nTHz frequencies. Moreover, the THz detection of analytes at picogram\nlevels is challenging. Here, a modern graphene-enhanced THz metasurface\nlabel-free sensor is presented. Its tunable resonance from ∼1.8\nto 2.6 THz matches the fingerprint resonant frequencies of various\nanalytes not currently detectable by label-free THz sensing. Quantitative\ndetection of trace 1,3-DNB (absorbing at ∼2.52 THz) is first\nachieved with a maximum reflectance sensitivity of ∼10% pmol<sup>–1</sup> and a detection limit of 42 pg. The sensor can also\nbe refreshed, minimizing cost and being more environmentally friendly.\nOur strategy expands application scenarios of label-free THz sensing,\nenhancing its potential in fields such as the pharmaceutical industry,\nenvironmental monitoring, and security.