Photonic cavity and graphene modified plasmonic interface for enhanced sensing performance

This study proposes a surface plasmon resonance (SPR) biosensor with enhanced sensitivity and improved bioaffinity by integrating modulation coupling and monolayer graphene. The strategy is to construct a one-dimensional (1D) photonic crystal (PC) cavity which consists of alternating high- and low-refractive index (RI) dielectric layers (i.e., Ta₂O₅ and Al₂O₃), forming a PC/Au configuration. As a result, a Fabry-Perot (FP) like resonance mode is introduced near the sensing surface, and the oscillating coupling between the PC-FP cavity and the surface plasmon contributes to the enhanced figure of merit (FOM) and high-sensitivity, reaching up to 8900 nm/RIU theoretically and 8052 nm/RIU experimentally. With a Finite-element method (FEM), an optimized prism/Ta₂O₅/(Al₂O₃+Ta₂O₅)¹/Al₂O₃/Au/Gra structure was obtained. Subsequently, a proof-of-concept experiment was carried out, and a fast Fourier transform (FFT) algorithm was applied to filter the detection noise. With the integration of monolayer graphene, the experimental sensitivity increased to 8128.3 nm/RIU. Furthermore, this biosensor performs a significant resonance shift of 6.53 nm when detecting 20 μg/mL human immunoglobulin G, 3.7-fold higher than the conventional detection. This novel design appeals to a wide range of biomedical applications requiring high sensitivity, better resolution, and easy fabrication.