The metasurface-enhanced fingerprint detection, endowed with their strong local electric field capabilities, provides a powerful platform to elucidate the trace molecular vibrational characteristics in terahertz band. However, the intrinsic refractive index of the analyte can induce a redshift in the resonant frequency, complicating the alignment of the resonant peak with the molecular absorption peak. Herein, we propose a reverse frequency matching strategy that effectively reduces the refractive index sensitivity of the designed metasurface, while simultaneously augmenting the local electric field, thus enhancing light-molecular coupling. By modulating the slot width to induce polarization sensitivity, the designed metasurface enables efficient molecular fingerprint sensing at dual polarizations while maintaining a refractive index sensitivity below 60 GHz/RIU and achieving an average electric field enhancement factor |E/E0| more than 36 times. As a proof of concept, we have demonstrated the qualitative and quantitative detection of L-cystine under two different polarizations, achieving the limits of detection as low as 0.219 μg/mm2. This achievement not only offers new insights into THz trace molecular fingerprint detection but also shows great potential in fields such as biosensing and polarimetric chemistry.
Hao et al. (Mon,) studied this question.