Broadband THz Molecular Fingerprinting Enabled by Brillouin Zone Folded Quasi‐BICs in Plasmonic Metasurfaces

Metasurfaces have emerged as a revolutionary platform for high‐performance terahertz (THz) sensing, particularly for biochemical trace detection. However, traditional metasurface sensors are fundamentally constrained by their inherent narrowband response, which restricts their molecular identification to isolated resonance frequencies. In this study, we propose a broadband and high‐sensitivity THz fingerprint metasensor by exploiting the scalability of perturbed Brillouin zone folding bound states in the continuum (BZF‐BIC). The design utilizes a mirror–symmetric, dual‐plasmonic elliptical resonator structure where a C 2 symmetry‐breaking perturbation is introduced to excite high‐ Q scalable quasi‐BIC (q‐BIC) modes characterized by strong localized field enhancement. Crucially, unlike traditional single‐frequency detection, our strategy establishes a series of high‐ Q resonant probes across discrete frequency channels, enabling the high‐sensitivity retrieval of molecular absorption fingerprints over a broad THz regime. Numerical simulations demonstrate that the proposed metasensor achieves an average 14‐fold enhancement in the extracted molecular absorption signal compared to bare substrate across 0.3 to 0.8 THz, facilitating the accurate identification of α ‐lactose, cis ‐azobenzene ( cis ‐AB), and benzoic acid. Furthermore, the sensor's capability for trace molecule identification and quantitative concentration analysis is experimentally validated using cis ‐AB. This work offers a robust and versatile avenue for highly sensitive, broadband on‐chip THz spectroscopic analysis systems.