High- <i>Q</i> terahertz metasurface biosensor based on bound states in the continuum

Abstract 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 quasi -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 −1 , which is significantly better than the performance of existing metal-based BIC sensors. The underlying mechanisms of the three quasi-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.