Terahertz Metasurface with Ultrastrong Hotspots Empowered by QBIC

A quasi-bound state in the continuum (QBIC) has been recognized as an excellent platform for enhancing light-matter interactions. When combined with metasurfaces, it enables ultrasensitive biosensing. However, the limited hotspots and heterogeneous spatial distribution of sample molecules restrict the advancement of QBIC metasurface detection. Here, we propose a terahertz (THz) metasurface biosensor, in which a geometric symmetry-breaking perturbation strategy successfully excites a QBIC resonance with a dynamically tunable quality (Q) factor. Compared to conventional Dipole resonance, the hotspot regions and light field intensity are enhanced by ∼1300% and 200%, respectively. Experimental results show that the sensor achieves highly sensitive, label-free quantitative detection of lung cancer cells, with a minimum detection concentration of 200 cells/mm 2 . Moreover, ionic liquids (ILs) modification effectively suppresses the coffee-ring effect, addressing the heterogeneous analyte distribution. This enables the sensor to achieve an ultralow direct limit of detection (LoD) for uridine diphosphate glucose (UDP-glucose), reaching 0.977 pmol/μL. These findings demonstrate an effective approach for developing precise, rapid, and highly sensitive biodetection technologies, with strong potential for clinical applications in the early screening of lung cancer metastasis.