Dual-mode terahertz microfluidic sensor based on an asymmetric complementary metasurface

Integrating terahertz metasurfaces with microfluidic chips provides a promising route for label-free sensing by enhancing light matter interaction while reducing the effective absorption path length in aqueous analytes. However, conventional terahertz microfluidic metasensors are often limited by insufficient near-field overlap with the analyte and by their reliance on a single high-performance resonance mode. Here, we propose a dual-mode terahertz microfluidic refractive index sensor based on an asymmetric I-shaped complementary metasurface. The laterally offset complementary slots introduce two effective resonant paths, enabling the simultaneous excitation of two absorption modes without extra structural complexity. Benefiting from the slot-dominated field confinement and strong field-analyte overlap, the proposed sensor achieves dual-frequency refractive index sensing with sensitivities up to 686 GHz RIU −1 while maintaining high absorptivity in both modes. These results demonstrate that the proposed complementary metasurface provides an effective strategy for high-performance terahertz microfluidic sensing, with potential applications in biomedical analysis, food safety, and liquid-phase chemical detection.