Investigation of SPR sensor for immunoglobulin detection by using Ag–\({{\text{Si}}}_{3}{{\text{N}}}_{4}\)-BP on the sensing layer

Surface plasmon resonance (SPR) has gained attention as a promising method for effective label-free biosensing. Immunoglobulin (IgG) detection is very important to understand the past infection and immunity of any individual. Thus, this study aims to develop a SPR sensor with better sensitivity for detecting IgG. It emphasizes the utilization of a high-performance planar waveguide-based SPR sensor to detect IgG by analyzing a suitable sensor topology. The sensor configuration consists of five distinct layers: silver (Ag), silicon nitride (\({{\text{Si}}}_{3}{{\text{N}}}_{4}\)), black phosphorus (BP), an enzyme, and a sensing medium. Silver (Ag) stimulates surface plasmons, while Si₃N₄ and BP are utilized to enhance absorption capabilities and serve as the bio-molecular recognition element, respectively. The proposed sensor simulation employs the transfer matrix method and an angular interrogation scheme. To assess this proposed sensor’s impact, the sensing region is assessed while considering three layers: Ag, Ag-BP, and Ag–Si₃N₄. Initially, the thickness of the Ag layer is optimized by recording its transmittance and achieving a minimum transmittance of 0.0027 at a thickness of 50 nm. Subsequently, the performance parameters are assessed using four different structures with slight variations in the IgG samples. The results depict the maximum achieved sensitivities as follows: 192 \(^\circ /{\text{RIU}}\) for conventional SPR, 203 \(^\circ /{\text{RIU}}\) for BP-based SPR, 287 \(^\circ /{\text{RIU}}\) for Si₃N₄-based SPR, and 352 \(^\circ /{\text{RIU}}\) for the proposed structure. This comparative study demonstrates that the proposed SPR configuration significantly enhances sensitivity, quality factor, and detection accuracy performance.