Ultrasensitive SPR cortisol biosensor utilizing MoS2 quantum dots/black phosphorus-based structure

This study presents a computational framework for an ultrasensitive, label-free surface plasmon resonance (SPR) biosensor tailored for physiological cortisol detection. Utilizing the Transfer Matrix Method (TMM) under TM-polarized illumination, we optimized a Kretschmann-based multilayered architecture comprising a low-refractive-index FK51A prism, a silver (Ag) plasmonic film, and a hybridized 2D material interface of molybdenum disulfide quantum dots (MoS₂ QDs) and black phosphorus (BP). Systematic numerical evaluations across the physiological refractive index (RI) spectrum of cortisol (1.3297–1.3311) identified the optimal configuration as FK51A / MoS₂ QDs (5 nm) / Ag (45 nm) / BP (9.54 nm, 18 monolayers). This finalized optoelectronic model demonstrated exceptional photon-plasmon conversion, effectively mitigating internal optical damping while preventing spectral broadening. The proposed biosensor achieves a remarkable peak angular sensitivity of 640.66 °/RIU at an analyte RI of 1.3300. Crucially, the design overcomes the traditional trade-off between sensitivity and spectral resolution, yielding a Quality Factor (Figure of Merit) of 99.314 RIU⁻¹ and a Detection Accuracy of 0.0297 deg⁻¹ . These tightly confined electromagnetic metrics establish the proposed MoS₂ QD/BP architecture as a robust, highly competitive theoretical platform for the accurate, real-time clinical monitoring of trace endocrine markers.