Dual-band terahertz microfluidic sensor based on spoof localized surface plasmon ring resonators

Metasurface-integrated microfluidic chips have emerged as promising platforms for terahertz refractometric sensing of trace liquid samples. However, achieving multiple independently addressable sensing bands remains challenging because closely spaced resonant modes often suffer from mode hybridization and mutual electromagnetic coupling, which can degrade sensing performance and limit frequency flexibility. Here, we propose a polarization-independent dual-band terahertz microfluidic sensor based on spoof localized surface plasmon ring resonators. The device integrates an outer dipolar ring resonator and an inner spoof localized surface plasmon ring resonator within a highly integrated metal–insulator–metal unit cell, enabling two strongly confined and highly isolated resonant modes. Owing to the weak electromagnetic cross-talk between the two resonators, the dual sensing bands can be independently tuned to match target spectral features while maintaining stable refractiveindex sensing responses. In addition, the centrosymmetric configuration ensures polarization-insensitive operation under arbitrary incident polarization angles. This design provides a flexible and robust route toward multiband terahertz biosensors with independent sensing frequencies, high mode isolation, and polarization-independent sensing performance.