Tunable coupling of collective resonances in plasmonic metasurfaces for multifunctional biosensing.

Plasmonic bound states in the continuum (BICs) serve as an ideal platform for enhancing light-matter interactions. However, traditional BIC-based sensors predominantly utilize quasi-BICs converted from symmetry-protected BICs for sensing, whereas the sensing capabilities of accidental BICs (aBIC) remain to be explored further. In this Letter, we propose a BIC-driven plasmonic sensor that supports an aBIC arising from the coupling between a quasi-BIC and another resonant mode. Tuning far-field radiation and the interaction between plasmonic BIC and mirror-induced BIC enables accurate regulation of weak coupling. By utilizing quasi-aBICs, the proposed sensor supports pixelated molecular sensing and achieves bulk refractive index sensitivity of 544.22 nm/RIU and surface sensitivity of 16 nm/nm. This work addresses diverse sensing requirements, advancing the design of on-chip nanophotonic devices.