Dual‐band high‐Q quasi‐BIC metasurface for refractive index sensing

Sensitive and miniaturized optical sensing device is highly desirable in various biosensing applications. This study reports a dual-band, high-quality-factor (<i>Q</i> factor) quasi-bound states in the continuum (quasi-BIC) metasurface for refractive index sensing, operating across the visible (700-800 nm) and near-infrared (950-1,000 nm) spectral ranges. By incorporating asymmetric dual nanoholes into an all-dielectric silicon metasurface, symmetry-protected BIC modes are transformed into quasi-BIC, resulting in two distinct Fano-type resonance peaks. Numerical simulations and experimental validations demonstrate that precise control over resonance wavelengths and quality factors can be achieved by adjusting the nanohole radius and positional offsets (Δ), yielding a theoretical <i>Q</i>-factor of 2,250. The sensor exhibits a refractive index sensitivity of 151.6 nm/RIU for the visible band (Q-BIC I) and 61.1 nm/RIU for the near-infrared band (Q-BIC II), with a signal-to-noise ratio (SNR) of 285, significantly outperforming existing nanohole-based biosensors. Fabricated using CMOS-compatible processes, the device employs cost-effective visible-light detectors, eliminating the need for specialized infrared materials. This work advances the development of high-sensitivity, miniaturized refractive index sensing platforms, offering promising applications in biomedical diagnostics and environmental monitoring.