Graphene-driven metal-free ultra-narrowband THz biosensor with reconfigurable wideband absorption

Abstract This work presents, for the first time, a compact, completely metal-free terahertz (THz) biosensing absorber consisting of a graphene bottom sheet, a SiO 2 spacer, and patterned dual graphene rings. It enables both ultra-narrowband and wideband absorption within a single platform. The dual-ring geometry gives two highly confined resonances at 1.602 THz and 2.346 THz with peak absorptions of 99.988% and 99.9868%, respectively, yielding excellent sensing metrics including maximum sensitivities of 1.06 and 1.25 THz RIU −1 , figures of merit of 18.714 and 17.401 RIU −1 , and quality factors of 28.253 and 32.816. Meanwhile, the structure is polarisation-insensitive and maintains its high absorption for incident angles as high as 75° (TE) and 65° (TM). Moreover, with the incorporation of phase-transition VO 2 , the absorber can also operate as a reconfigurable >90% wideband absorber in the frequency range of 1.1165–3.608 THz. Therefore, these results place the proposed absorber as a tunable, low-loss, and intelligent THz sensing platform for virus detection, cancer diagnostics, and biochemical monitoring.