Novel Quad Band Terahertz Absorber-Based Biosensor for Label-Free Detection of Carcinoma

A novel terahertz (THz) metamaterial absorber is studied in this paper for label-free cancer cell identification. The proposed absorber has a compact electrical footprint of 0.596 λ₀ × 0.596 λ₀, where λ₀ is the free-space wavelength at the lowest operating frequency of 2.75 THz. The absorber exhibits quadband resonance at 2.75, 2.95, 3.18, and 3.38 THz through a multi-resonator configuration consisting of an outer square loop, a middle octagonal resonator, and an inner convoluted ring resonator. These resonators collectively shape the absorption spectrum, producing narrow and distinct absorption peaks for precision biosensing. The absorber is designed using polyimide material with graphene used as the conductive layer, enabling high conductivity and tunability at THz frequencies. The absorber exhibits strong absorption above 98% at all four resonant frequencies, and its rotational symmetry ensures polarisation insensitivity. It also maintains good angular stability up to 60°, ensuring robust performance under oblique incidence. The narrow absorption bandwidths enhance its effectiveness for detecting subtle dielectric variations in biological tissues. Optimisation using the Firefly metaheuristic algorithm results in a minimum average sensitivity of 325 GHz/RIU at 2.75 THz and maximum average sensitivity of 858 GHz/RIU at 3.18 THz across the four frequency bands and a minimum average figure of merit (FoM) of 36.11/RIU at 2.75 THz and maximum average FoM of 95.37 RIU -1 at 3.18 THz. These features establish the proposed design as a promising candidate for early-stage carcinoma detection in the THz domain.