Terahertz Quasi-BIC Metasurfaces for Ultra-Sensitive Biosensing and High-Speed Wireless Communications

Bound states in the continuum (BICs) have emerged as a revolutionary paradigm in terahertz (THz) photonics, enabling metasurfaces with theoretically infinite quality factors (Q-factors) and unprecedented light-matter control. This review synthesizes a decade of progress in THz-BIC research, tracing the evolution from foundational symmetry-protected designs to application-optimized quasi-BICs. We dissect multipolar origins, topological robustness, and symmetry-breaking strategies underpinning high-Q resonances, alongside computational frameworks for predictive design. The timeline highlights key milestones: early dielectric metasurfaces with high Q-factor, flexible biosensors achieving microgram detection limits, and Kerker-conditioned gas spectrometers reducing path lengths by few orders of magnitude. Emerging frontiers in reconfigurable MEMS-BICs and chiral quantum photonics are critically evaluated. Despite breakthroughs, scalability barriers persist for 6G integration, including nano-fabrication tolerances, material loss trade-offs, and dynamic control gaps. This review establishes BIC metasurfaces as pivotal enablers of compact, high-efficiency THz technologies poised to bridge the gap between fundamental discovery and commercialization of THz-based 6G communication and MedTech.