Multifunctional bio-enzyme sensor empowered by bound states in the continuum via a Si-VO₂ metasurface

Bound states in the continuum (BIC) present a novel avenue for advancing high-quality factor metasurfaces, promising in high-performance lasers, sensors, and nonlinear optical devices at the nanoscale. Currently, sensors designed based on BIC have achieved good sensing performance. However, the functionality of current metasurface sensors is relatively singular, rendering them less chance in complex sensing scenarios. Specifically, taking a bio-enzyme metasurface sensor as an example, since different bio-enzymes have different optimal reaction temperatures, it is mostly inescapable to design multiple metasurface sensors for different bio-enzyme detection. In this paper, we developed a multifunctional sensor that can adapt to different reaction temperatures of bio-enzymes, meeting the requirements of multiple scenarios. The proposed metasurface consists of two elliptical cylinders, which can excite a high-Q quasi-BIC resonance by changing their rotation angles. By introducing VO₂ film, external ambient temperature can effectively manipulate the transmission modulation depth and quasi-BIC. Simulation results show the maximum relative modulation depth of the metasurface can reach 296%. When combined with bio-enzymes, the metasurface serves as a refractive index sensor with a sensitivity as high as 370 nm RIU⁻¹ at 30 °C and 80 °C. Our work provides insights for the design of highly integrated and tunable devices in the future.