Ultra-sensitive hybrid metamaterial–plasmonic sensor based on a split-ring resonator metasurface for refractive index biosensing

Abstract

Optical biosensors have become essential tools for rapid and label-free detection of biological analytes in medical diagnostics and environmental monitoring. However, conventional plasmonic sensors often suffer from broad resonance linewidths and limited light–matter interaction, which constrain their sensing resolution and figure of merit (FOM). In this work, we propose a novel hybrid metamaterial–plasmonic biosensor based on a split-ring resonator (SRR) metasurface integrated with metallic nanoparticles to simultaneously enhance electromagnetic field confinement and optimize resonance characteristics. The proposed architecture exploits hybrid coupling between the SRR resonance and the localized surface plasmon resonance (LSPR) of metallic nanoparticles through a dielectric SiO₂ spacer layer, leading to the formation of hybrid modes. The underlying physical mechanism is validated through photonic band structure analysis, which reveals pronounced anticrossing behavior, and through energy band alignment that confirms efficient dielectric isolation and strong near-field coupling. Electromagnetic responses are analyzed using finite-difference time-domain (FDTD) simulations, and systematic optimization of the structural parameters is performed to maximize sensing performance. The optimized design achieves a resonance wavelength shift of 140 nm for a refractive-index variation of 0.15 RIU over the biologically relevant range of 1.33–1.48, corresponding to a sensitivity of 930 nm/RIU, a resonance linewidth of 55 nm, a quality factor of 13.33, and a figure of merit of 16.91. These results indicate a moderate-Q, hybrid SRR–plasmonic sensing platform whose performance is reported here without comparison to ultra-high-Q or q-BIC sensing architectures.