High-Sensitivity Optical Sensors Empowered by Quasi-Bound States in the Continuum in a Hybrid Metal–Dielectric Metasurface

Enhancing light–matter interaction is a key requisite in the realm of optical sensors. Bound states in the continuum (BICs), possessing high quality factors ( Q factors), have shown great advantages in sensing applications. Recent theories elucidate the ability of BICs with hybrid metal–dielectric architectures to achieve high Q factors and high sensitivities. However, the experimental validation of the sensing performance in such hybrid systems remains equivocal. In this study, we propose two symmetry-protected quasi-BIC modes in a metal–dielectric metasurface. Our results demonstrate that, under the normal incidence of light, the quasi-BIC mode dominated by dielectric can achieve a high Q factor of 412 and a sensing performance with a high bulk sensitivity of 492.7 nm/RIU (refractive index unit) and a figure of merit (FOM) of 266.3 RIU –1, while the quasi-BIC mode dominated by metal exhibits a stronger surface affinity in the biotin–streptavidin bioassay. These findings offer a promising approach for implementing metasurface-based sensors, representing a paradigm for high-sensitivity biosensing platforms.