A tunable graphene terahertz sensor with high sensitivity and figure of merit for refractive index biosensing

This study presents the design, numerical modeling, and performance analysis of a tunable graphene-based terahertz (THz) sensor exhibiting multiband resonance behavior. The proposed device leverages the unique electro-optical properties of graphene, where modulation of the chemical potential (V) enables dynamic control over the electromagnetic response. This tunability allows real-time ON/OFF operation and precise frequency reconfiguration, resulting in enhanced adaptability for diverse sensing scenarios. The sensor supports four distinct resonance modes at 0.22, 0.35, 0.70, and 0.88 THz, covering a wide portion of the THz spectrum and making it particularly suitable for multiband detection. Simulation results reveal that increasing the chemical potential shifts all resonance modes toward higher frequencies, a consequence of enhanced graphene conductivity and improved impedance matching between the sensor and the surrounding medium. This frequency agility is critical for applications where detection bands need to be dynamically selected or reconfigured. The proposed design exhibits sharp resonance dips, high spectral selectivity, and elevated sensitivity, leading to an impressive figure of merit (FOM) of up to 5.30 RIU⁻¹ across all operational modes. For a refractive index range of 1.0-1.1, the device achieves sensitivities of 0.51, 0.85, 1.87, and 0.212 THz/RIU for the first to fourth modes, respectively, all within the 0.1-1.0 THz operational window. Such performance metrics position the sensor as a promising candidate for next-generation THz biosensing, non-invasive medical imaging, and chemical or environmental detection, where rapid, reconfigurable, and label-free measurements are essential. Moreover, the multiband capability and tunable nature of the graphene platform open avenues for integrated lab-on-chip sensing systems with adaptive, high-precision operation.