Design considerations of highly sensitive dual resonance metasurface grating biosensor

This study introduces a highly responsive surface plasmon resonance (SPR) optical sensor and an all-dielectric metasurface for monitoring water salinity and glucose levels in blood. We present optimized low-cost microfluidic sensors capable of measuring water salinity (0%-40%, refractive index 1.333-1.341) and successfully detecting glucose solutions (5%-50%, refractive index 1.32-1.41). The metasurface of both structures, designed for high sensitivity, is proposed and numerically simulated in the visible and near-infrared spectral ranges. The SPR sensor consists of a multilayer grating made of Si₃N₄ and Al₂O₃ placed on a silver layer, with a SiO₂ substrate. To reduce fabrication costs, the Si₃N₄ layer was replaced with silicon, and the plasmonic layer was eliminated. The sensor was optimized for sensitivity and accuracy using finite difference time domain simulations via Lumerical software. For water salinity detection, both plasmonic and all-dielectric sensors achieved a maximum sensitivity of 167 nm/RIU and 459 nm/RIU, respectively. The sensors also accurately detected sugar concentrations, with maximum sensitivities of about 157 nm/RIU and 542 nm/RIU for the SPR and all-dielectric structures, respectively.