Refractive Index Biosensor Using Metamaterial Perfect Absorber Based on Graphene in Near-Infrared for Disease Diagnosis

This paper presents a metamaterial perfect absorber as a biosensor in the near-infrared region for biomedical molecular detection, such as urine concentration, malaria infection, bacillus bacteria, and cancer cell detection. In the proposed biosensor, an Au layer with a bracket-shaped cavity is utilized to boost electric field enhancement intensity in the vicinity of the nanohole. According to the capacitance of the bracket-shaped nanohole, changing the length of the hole controls the resonance wavelength. Due to the significant confinement of the electromagnetic field in the sharp edges and gaps, which excites Localized Surface Plasmon Resonances (LSPRs) in the metal-dielectric interface, near-unity absorption is obtained. Through evaluating the optical responses of the structure, via the finite element method (FEM), for different biomedical samples, high sensitivity of 2120.86 nm/RIU is acquired. In order to increase the sensitivity of the biosensor, a graphene layer is added between the dielectric layer and the gold nanohole layer. Adding graphene increases the LSPRs excitation and losses which yields a maximum sensitivity of 2500 nm/RIU. The presented biosensor with high sensitivity and compact size is a good candidate for biomedical purposes.