High-sensitivity terahertz biosensing via a plasmon-induced transparency metamaterial with dual-resonance response

In this work, a terahertz metamaterial biosensor that exhibits plasmon-induced transparency (PIT) is presented. This biosensor allows for the label-free, very sensitive detection of biological analytes. The proposed unit cell combines two split-ring resonators with two rectangular metallic rods. Each resonator has a semicircular shape perforated with elliptical slots. The transparency window exhibits dual-resonance behaviour at 2.045 THz and 2.455 THz. These resonances result from the interaction of bright and dark modes, with minimum loss. The PIT mechanism is explained using electric field distribution analyses. These results demonstrate significant mode coupling and field localization. To demonstrate its practical utility, the sensor's reaction to different refractive indices associated with COVID-19-related biomaterials is investigated. At the higher-frequency resonance, the sensor reaches a sensitivity of 696.808 GHz/RIU at a refractive index (RI) of 1.47. Additionally, the PIT biosensor achieves a quality factor of 16.88, a figure of merit of 5.53, a detection limit of 0.0949, and a detection accuracy of 7.938. This enables precise detection through its refractive index changes. Furthermore, the structure enables PIT-assisted bound states in the continuum (BIC), which improves the quality factor and detection resolution. These results demonstrate that PIT in THz metamaterials enables narrow resonances with strong field enhancement, providing a cost-effective platform for ultrasensitive, label-free biosensing applications for enhanced biological diagnostics.