An Enhanced Terahertz Metasurface Biosensor Based on Reduced Substrate Effect and QBIC Resonance

This paper presents an enhanced square-ring absorber (ESR-absorber) terahertz metasurface biosensor based on reduced substrate effect and quasi-bound states in the continuum (QBIC) resonance. By optimizing the fieldsample interaction region, the biosensor achieves a sensitivity of 0.24 THz/RIU in the metasurface perfect absorber (MPA) mode-a$2.76-4.29 \times$improvement over conventional architectures-and 0.425 THz/RIU in the QBIC mode, corresponding to a$4.89-7.59 \times$enhancement. The proposed sensor is applied for the specific detection of FGFR2 membrane protein in clinical gastric cancer tissue samples across varying pathological grades, with all results validated against a$3 \sigma$noise floor. This work enables rapid, highly sensitive, and specific gastric cancer diagnosis and monitoring, establishes FGFR2 as a practical biomarker, and overcomes the limitations of traditional sensors imposed by substrate-confined field effects.