Symmetry-Breaking-Induced Quasi-Bound States in the Continuum in All-Dielectric Terahertz Metasurface for High-Sensitivity Refractive Index Sensing and Theoretical Virus Differentiation

Bound states in the continuum (BIC) have recently attracted extensive research interest, owing to their exceptional capability for light confinement and high quality-factor (Q-factor) resonances. In this work, we design an all-dielectric terahertz metasurface based on the symmetry-breaking properties of silicon rectangular pillars. Numerical simulations demonstrate that breaking the in-plane inversion (C2) symmetry transforms the BIC into a quasi-BIC (q-BIC), which features a high Q-factor and a narrow resonance linewidth. Through far-field multipole decomposition and near-field electromagnetic field distribution analysis, the excitation mechanism of the q-BIC mode is elucidated, revealing that the magnetic dipole (MD) contribution remains predominant over a certain range of asymmetry. Furthermore, the q-BIC resonance exhibits high sensitivity to the change in refractive index, achieving a theoretical sensitivity of 110 GHz/RIU even with an analyte thickness of only 15 μm. When MS2 and PRD1 bacteriophages are employed as model analytes with distinct effective refractive indices, the sensor produces a larger resonance frequency shift for MS2 than for PRD1, demonstrating its capability for theoretical dielectric discrimination based on refractive index differences. These findings provide a valuable reference for the development of all-dielectric terahertz metasurface platforms for label-free refractive index sensing and model virus differentiation.