Dual-band polarization insensitive graphene biosensor for THz medical applications

Abstract

Abstract This paper presents a dual-band terahertz (THz) biosensor based on concentric graphene rings on a Topas substrate with a gold ground plane, designed for refractive index (RI) sensing and early disease detection. A systematic design evolution from single to dual graphene rings demonstrates electromagnetic coupling for enhanced dual-band operation. The biosensor compact structure (8 × 8 µm 2 ) achieves near-perfect absorption through localized surface plasmon polaritons, with optimized dimensions yielding resonances at 1.69 THz and 2.90 THz. The absorption efficiencies of 99.83% and 99.73%, and FWHM of 165.4 GHz and 0.110 GHz, respectively are achieved. The graphene loops tunability is enabled via Fermi energy ( µ c = 0.5–0.8 eV) and relaxation time ( τ = 0.5–3 ps), shifting resonances up to 0.35 THz while maintaining > 99% absorption. Parametric studies reveal optimal performance with polarization insensitivity (identical TE/TM responses), and angular stability (> 85% absorption up to 80° incidence). For RI sensing ( n = 1–1.5), the biosensor exhibits sensitivities of 578–988 GHz/RIU (1st peak) and 957.6–1419 GHz/RIU (2nd peak), figures of merit (FOM) up to 9.88 and 12.78 RIU⁻¹, and quality factors ( Q ) of 13–15 and 20–24, respectively. Robustness to non-uniform analyte distributions (such as, nonuniformity, air bubbles, partial filling) is shown, with < 15% degradation in sensitivity and FOM. The concentric graphene architecture enabling dual-band, high-Q resonances with superior sensitivity facilitating biomedical applications in label-free detection of cancers (blood, breast; sensitivities 1–2.5 THz/RIU) and viruses (HVS vs. Influenza; Δ f ≈ 19–34 GHz for Δ n = 0.07).