Design and Performance Analysis of an SPR Sensor for Milk Adulteration Monitoring

Hydrogen peroxide (H₂O₂) may be illegally added to milk to delay visible spoilage, producing concentration-dependent changes in its refractive index. This study numerically evaluates the optical response of a B-sil/Al/Al₂O₃/WS₂ surface plasmon resonance (SPR) configuration to these refractive-index variations. The angular SPR response was calculated at λ = 633 nm using the transfer matrix method under TM-polarized illumination. The B-sil/Al/Al₂O₃/WS₂ architecture was established through sequential evaluation of prism material, Al thickness, Al₂O₃ thickness, and 2D interfacial material, followed by assessment of its response to H₂O₂-associated refractive-index changes in milk. The final structure consisted of 70 nm Al, 25 nm Al₂O₃, and 0.80 nm WS₂. Across the simulated H₂O₂ conditions, the resonance angle shifted from 85.65° to 86.11°, while the angular sensitivity ranged from 383.82 to 406.45°/RIU. The best balance among the evaluated metrics was obtained for H₂O₂-C2, with a sensitivity of 406.45°/RIU, QF of 4.65 RIU^-1, FoM of 436.48 RIU^-1, LoD of 1.23 × 10^-5, and CSF of 436.56. The WS₂-containing interface produced calculated angular shifts for small refractive-index variations in the milk sensing medium. Comparison with reported SPR systems for milk-related sensing showed a comparable angular sensitivity range, while QF and detection accuracy were limited by the broad resonance profile. These results characterize the theoretical optical response of the B-sil/Al/Al₂O₃/WS₂ multilayer under H₂O₂-associated refractive-index changes but do not establish chemical selectivity toward H₂O₂. Experimental implementation would require an appropriate selective filtering or recognition strategy, together with validation of matrix effects and practical sensing performance.