Ultrasensitive mid-infrared metasurface sensing governed by quasi-bound states in the continuum

Abstract

Quasi-bound states in the continuum have demonstrated significant advantages in enhancing the sensitivity of optical sensing, while it remains challenging to achieve dual-resonance sensing that exhibits excellent sensitivity simultaneously. Here, we demonstrate an all‑dielectric metasurface in the mid‑infrared region to achieve a quasi‑bound state in the continuum resonance by breaking structural symmetry, reaching a Q-factor of 1.27 × 10⁵. Multipolar decomposition and field distributions reveal that the resonances are dominated by toroidal dipole contributions. The proposed metasurface behaves as an excellent sensing platform, achieving high sensitivities of up to 5348 nm/RIU and 5338 nm/RIU for gas sensing, and 3419 nm/RIU and 3403 nm/RIU for blood component detection. The dual high-sensitivity resonances further enable independent refractive-index retrieval and dual-channel consistency verification, improving the overall sensing reliability. The proposed metasurface provides new insights for high-performance sensing schemes operating in the mid-infrared region.