Borophene-based dual-mode metasurface biosensor with a dynamically tunable PIT-like effect

Optical biosensors based on plasmon-induced transparency (PIT) metasurface hold great promise for label-free biodetection, but conventional plasmonic and 2D materials suffer from limited electrical tunability, low carrier density, and poor broadband adaptability, severely restricting their performance in high-precision, dynamically adjustable near-infrared (NIR) sensing. Here, to address the limited tunability of conventional plasmonic biosensors, a dynamically tunable borophene-based dual-mode metasurface (DMM) architecture is proposed. It exploits the ultrahigh electron density and broadband electrical tunability of χ₃-phase borophene to realize a dynamically tunable bulk RI transduction architecture, and proposes its potential application for biosensing. The PIT-like response originates from the bright-bright mode coupling between vertex-vertex and base-base triangular borophene dimers, which is systematically elucidated via FDTD simulations and temporal coupled-mode theory. Electrical gating allows continuous tuning of electron density (3 × 10¹⁹-7 × 10¹⁹m^-2), yielding a significant blue-shift of resonant dips, narrowed linewidths, and enhanced quality factors (Q-factor). The sensor delivers dual-channel refractive index (RI) sensing with maximum sensitivities (S) up to 875.7 nm/RIU and 1064.3 nm/RIU, accompanied by high linearity (R² > 0.99) and strong substrate robustness. This work presents an electrically tunable χ₃-borophene-based DMM architecture as a near-infrared bulk RI transduction platform, which relies on PIT-like bright-bright mode hybridization. The present study aims to elucidate the intrinsic modal behavior and electrically tunable sensing characteristics of the proposed conceptual architecture, while validation for application-oriented biosensing is reserved for future work.