Novel quad band terahertz absorber-based biosensor for label-free detection of carcinoma

Abstract 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 λ 0 × 0.596 λ 0 , where λ 0 is the free-space wavelength at the lowest operating frequency of 2.75 THz. The absorber exhibits quad band 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 bio-sensing. 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° with absorptivity above 80%, 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 −1 at 2.75 THz and maximum average sensitivity of 858 GHz RIU −1 at 3.18 THz across the four frequency bands and a minimum average figure of merit (FoM) of 36.11 RIU −1 at 2.75 THz . These features establish the proposed design as a promising candidate for early-stage carcinoma detection in the THz domain.