Ultrasensitive Terahertz Metasurface Biosensor Based on Quasi‐Bound States in the Continuum (Laser Photonics Rev. 20(11)/2026)

Ultrasensitive THz Biosensing via QBICs In Research Article e03194, Yan Meng, Xiang Xi, Hongcheng Wang, Zhen Gao and co-workers report an asymmetric split-ring metasurface that harnesses quasi-bound states in the continuum (QBICs) to balance ultrahigh confinement and radiative coupling. The device enables label-free detection of cysteine with a sensitivity of 492 GHz/RIU and an ultralow detection limit down to 0.00025 mg mL−1. The observed logarithmic-to-linear concentration dependence transition reveals distinct sensing regimes, providing insight into trace-level terahertz biochemical detection.