Prottay Biswas, Md Abu Shahid Chowdhury, Md Bashir Uddin
Surface plasmon resonance (SPR) biosensors have become a mainstay in the study of biological samples and the detection of disease biomarkers with unprecedented sensitivity and maximum accuracy in a label free manner. However, optimizing the sensor design remains a crucial issue that needs to be addressed to ensure accurate detection of analytes. This study presents a highly sensitive SPR biosensor system that detects cortisol, a key indicator of physiological stress, using the modified Kretschmann configuration. A BK7 glass prism, silicon (Si) adhesive layer, bimetallic silver/palladium (Ag/Pd) film, blue phosphorus-tungsten diselenide (BlueP-WSe 2 ) monolayer, and silicon nitride (Si 3 N 4 ) anti-reflective coating comprise the multilayer design of the sensor. The sensor structure was optimized using finite-difference time-domain (FDTD) simulations. The optimized design achieved the highest sensitivity of 387.96 deg/RIU, a quality factor (QF) of 83.729 RIU⁻¹, and a detection accuracy (DA) of 0.4186 over the refractive index (RI) range of 1.330–1.335. It showed a notable 206.78% improvement in sensitivity and a 166.06% improvement in QF compared to the traditional prism/Ag-based configuration. Incorporation of the BlueP-WSe 2 layer elevated the light confinement which further enhanced the overall sensor performance. When applied to detect cortisol, the sensitivity gradually increased with the analyte concentration and reached a peak sensitivity of 343.14 deg/RIU. The results also demonstrated a very high DA, QF, and a small limit of detection (LOD) of 0.1055, 75.375 RIU⁻¹, and 2.914 × 10 -6 RIU⁻¹, respectively. This work introduces an SPR biosensor for cortisol detection, offering an outstanding performance and paving the way for more reliable and accurate stress biomarker detection.