Leveraging two-dimensional materials for high-sensitivity optical sensors: quasi-bound states in the continuum within hybrid metasurfaces

Hybrid metal-dielectric metasurfaces supporting quasi-bound states in the continuum (qBICs) provide a powerful platform for high-Q optical sensing. In this work, we leverage two-dimensional materials as functional interlayers in a hybrid metal-dielectric metasurface to enable material-driven regulation of qBIC resonances for sensing applications. This approach introduces a material-assisted perturbation mechanism that enables tuning of the qBIC response within the same structural framework, without re-optimizing the overall geometry in the present design. Numerical simulations reveal that different two-dimensional materials modulate qBIC resonances through distinct physical mechanisms. Graphene enhances surface field coupling by modifying electromagnetic boundary conditions, while MoS₂ introduces refractive-index loading and additional loss channels that reshape field confinement. Consequently, the resonance linewidth is reduced from 1.85 nm in the bare structure to 1.36 nm with graphene and further to 1.20 nm with molybdenum disulfide, corresponding to an increase in the quality factor (Q factor) from 412 to 633, together with a bulk sensitivity of 485 nm/RIU and an improved figure of merit of 404.2 RIU⁻¹. Furthermore, the influence of the graphene Fermi level is numerically investigated to evaluate the potential tunability of the resonance linewidth and depth, providing additional flexibility for sensor optimization. These results indicate that two-dimensional materials can serve as effective functional interlayers for modulating qBIC resonances in hybrid metasurfaces, and can provide a practical route toward compact, high-resolution optical sensing platforms.