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.