Dual-mode Q-BIC metasurface supporting Goos–Hänchen shifts for highly sensitive optical biosensing applications

Abstract

Bound state in continuum (BIC) driven photonic structures emerged as a cornerstone for achieving strong control over radiative losses and generating ultra-sharp spectral features, capabilities that are difficult to realize with conventional photonic resonators, thereby offering a versatile platform for light manipulation at the subwavelength scale. Here, the dual Quasi-BIC (Q-BIC) modes originated from the non-degeneracy between forward and backward propagating modes in an L-shaped grating-based metasurface, resulting in a significant enhancement in the Goos–Hänchen shift (GH shift) for both resonances. Both modes are examined for refractive index-based sensing. Finally, the designed metasurface is used as a biosensor for sensing electrolytes $K^{+}$, $N{a}^{+}$, and non-electrolyte glucose. We achieved a sensitivity of 36.42 nm/RIU, 39.10 nm/RIU, and a notably higher 64.70 nm/RIU with a high FOM (figure of merit) for $K^{+}$, $N{a}^{+}$, and glucose, respectively. Beyond biosensing, the high Q-factor makes it relevant for applications such as ultra-narrowband absorbers and phase-sensitive devices (e.g., beam-shaping or directive metasurface antennas), where precise control of light–matter interaction is essential.