High-Q terahertz metasurface biosensor based on bound states in the continuum

In recent years, metasurfaces driven by bound states in the continuum (BICs) have attracted much attention, but the low-Q factor is their common deficiency. Here, a high-Q terahertz metasurface consisting of four L-shaped resonator and two vertical metal rods deposited on a quartz substrate is presented. Three different BIC modes with high-Q factors are realized, with the third Q-BIC mode having the most prominent Q factor of 406.03, and thus it has the best sensing sensitivity compared to the first two BIC modes, reaching up to 366.3 GHz/RIU, which is significantly better than the performance of existing metal-based BIC sensors. The underlying mechanisms of the three Q-BIC modes are analyzed in depth according to multipole decomposition and near-field electromagnetic pattern distribution. The group delay characteristics of the designed metasurface is further studied, and an ultra-high group delay of 48 ps is achieved. Given the high-Q factor, sensitive sensing, and large group delay, this BIC-driven metal metasurface has significant potential in biomedical sensing and slow light devices.