Dual-resonance quasi-BIC metasurface for highly sensitive refractive-index sensing and biosensing applications

Quasi-bound state in the continuum (quasi-BIC) metasurfaces provide a promising platform for optical sensing due to their low radiative loss and narrow resonances. However, achieving stable sensing performance across different environments remains challenging. Here, we demonstrate a dual-resonance quasi-BIC metasurface based on asymmetric amorphous silicon nanopillar dimers, enabling sensing performance evaluation in both dry and liquid environments in the near-infrared region. The device exhibits two magnetic toroidal dipole (MTD)-dominated quasi-BIC resonances with refractive-index sensitivities of 162 nm/RIU and 609 nm/RIU. Both simulations and experiments demonstrate stable refractive-index sensing performance in dry and liquid environments, validating the applicability of the proposed metasurface under different operating conditions. The two resonances exhibit distinct sensing characteristics in different media, providing complementary responses for optical sensing. Owing to its simple structure, CMOS-compatible fabrication, and compatibility with microfluidic integration, the proposed metasurface provides a promising platform for optical sensing and biomolecular detection in different environments.