High Q-factor multiband terahertz metasurface biosensor for biomedical refractive index sensing: a numerical study.

Terahertz (THz) metasurface absorbers have emerged as promising platforms for biomedical sensing due to their high-quality (Q) resonances and strong sensitivity to dielectric variations in biological tissues. Conventional single-band designs are effective only over a narrow frequency range, reducing detection reliability and increasing false positives. This study introduces a polarization-independent multiband metasurface absorber (MSA) with good angular stability for label-free terahertz biosensing applications. The structure features a dual-metallic split-ring resonator with a continuous backside ground plane, arranged in a compact metal-dielectric-metal (MDM) pattern. The proposed absorber exhibits six absorption peaks with near-unity (> 98%) absorption at 1.80, 2.89, 4.65, 4.84, 5.12, and 5.84 THz. Furthermore, a Q-factor of 177, along with narrow full-width at half-maximum (FWHM) values, ensures exceptional spectral selectivity. The sensor exhibits sensitivities of up to 2.92 THz/RIU and 8 THz/RIU for refractive index ranges corresponding to reported cancer- and malaria-related biological samples, respectively. The resonances enhance light-matter interactions and improve refractive-index sensing performance through stronger electromagnetic field confinement. The proposed design provides a simple, high-Q, multiband platform for THz biosensing applications and is compatible with future microfluidic integration.