High-sensitivity biosensing of tryptophan based on a MoS₂-modified QBIC terahertz metasurface

This article presents high-sensitivity biosensing of tryptophan based on a molybdenum disulfide (MoS₂)-modified quasi-bound states in the continuum (QBIC) terahertz (THz) metasurface. By introducing structural asymmetry into double-racetrack resonators, a QBIC resonance is excited with a simulated refractive-index sensitivity of 450 GHz/RIU. To enhance analyte preconcentration, the quartz substrate was modified with a MoS₂ film, converting the surface from hydrophilic to hydrophobic. Comparative measurements between unmodified and MoS₂-modified metasurfaces demonstrate that the modification significantly improves the limit of detection for tryptophan, achieving fivefold and fourfold enhancements for the QBIC (0.005 nmol/µL) and dipole (0.05 nmol/µL) modes, respectively. This performance gain is attributed to the suppression of the coffee-ring effect and enhanced analyte accumulation at electromagnetic hotspots. The proposed method offers a label-free and cost-effective solution for trace-molecule detection in biomedical and environmental applications.