Development of a high-sensitivity multimode graphene-based metamaterial biosensor with a double-split elliptical resonator for refractive index sensing and biomedical applications.

This paper introduces a high-sensitivity, multimode graphene-based metamaterial (MM) biosensor for refractive index sensing, featuring a periodic array of gold (Au) double-split elliptical resonators (DSERs) on a graphene-coated silicon dioxide (SiO₂) substrate with an Au reflective base layer. The proposed design is analyzed using finite-difference time-domain (FDTD) simulations. The unique double-split elliptical geometry significantly enhances electromagnetic field confinement and enables the excitation of multiple distinct resonance modes, outperforming conventional circular or rectangular resonators that typically support only single- or dual-mode responses. The novelty of this work lies in the integration of a graphene-metal hybrid structure that combines tunable plasmonic properties of graphene with strong localized surface plasmon resonances of DSERs, resulting in multimode operation, improved tunability, and superior sensing performance. The bottom gold layer effectively suppresses transmission and reinforces field confinement within the active region. The sensor operates across 650-1500 nm, supporting five well-separated resonance modes that provide multiple sensing channels, enhancing detection efficiency and spectral flexibility. Optimized structural parameters such as the Au array thickness, SiO₂ layer thickness, and resonator width further improve its performance. The biosensor achieves a maximum sensitivity of 714.28 nm/RIU, a figure of merit (FoM) of 51.02 1/RIU, and a quality factor (QF) of 73.42 for breast cancer cell detection. Moreover, it successfully distinguishes between normal and cancerous cells (basal, breast, and cervical), demonstrating its strong potential for biomedical diagnostics and optical sensing applications. These results position the proposed multimode graphene-based biosensor as a promising platform for next-generation photonic and biomedical sensing technologies.