Angle- and geometry-multiplexed quasi-BIC metasurfaces for broadband molecular fingerprint trace sensing

Terahertz (THz) fingerprint spectroscopy provides a powerful, label-free, and nondestructive approach for identifying molecular species. Dielectric metasurfaces supporting quasi-bound states in the continuum (quasi-BICs) can significantly enhance light-matter interactions, offering extreme field confinement and a high quality-factor (Q-factor) that greatly improves detection sensitivity down to trace analyte levels. However, the realization of broadband molecular fingerprint retrieval remains challenging due to the intrinsically narrow bandwidth of quasi-BICs, limited resonant frequency tunability, and the lack of post-fabrication reconfigurability. Here, we propose an all-dielectric metasurface sensor with angle- and geometry-multiplexed architecture to overcome these limitations. The design leverages multi-degree-of-freedom optimization ­­— via incident angle and in-plane geometry variation ­­— to excite and tailor multiple high Q- factor quasi-BIC resonances, enabling coherent spanning of the wide spectral band from 1.2 to 2.2 THz. This approach allows enhanced fingerprint retrieval of glucose and fructose as representative isomers. Furthermore, the metasurface can be seamlessly integrated into on-chip platforms, providing a robust and highly sensitive strategy for trace molecular sensing and broadening the application prospects of THz technology in chemical and biomedical diagnostics.