Flexible terahertz metasurface supporting bound state in the continuum for refractive index based staphylococcus aureus sensing

Staphylococcus aureus (S. aureus) represents a major threat to global health, and its sensitive and accurate detection is highly demanded in disease diagnosis and food safety. Here, a flexible terahertz (THz) metasurface based on bound states in the continuum (BIC) is proposed and experimentally demonstrated for the trace analysis of S. aureus. The unit cell structure incorporates a metallic square with two opening gaps, supporting a resonance transition from BIC to quasi-BIC states by introducing a symmetry perturbation to one opening gap location. Firstly, the refractive index (RI) spectra of the drip-dried S. aureus solution at different concentrations are characterized using THz-TDS. The frequency point possessing a maximum linearity between RI and S. aureus concentrations is selected as the resonance frequency of designed sensing quasi-BIC. Moreover, an experimental demonstration of the sensing performance is conducted by monitoring spectral evolution after target loading. The measured results indicate that the constructed biosensor exhibits a detection limit down to 200 cfu/mL and RI sensing sensitivity up to 267.1 GHz/RIU for S. aureus measurement. Hence, the flexible, easy manufacturing, and highly-sensitive quasi-BIC metasurface biosensor paves a new way toward developing novel bacteria sensors and BICs-related optoelectronic devices.