Design and Numerical Optimization of a Borosilicate-Supported Aluminum SPR Sensor for Monitoring Metal Ion Mixtures

Heavy metal contamination in aquatic environments represents a major environmental and public health concern due to the toxicity and bioaccumulation of ions such as HgII, PbII, and ZnII. Laboratory-based techniques such as AAS and ICP-MS provide high sensitivity but often require specialized instrumentation and off-site analysis. Surface Plasmon Resonance (SPR) sensors offer a complementary label-free route for real-time optical monitoring due to their rapid response and sensitivity to refractive-index changes. The optical response of the proposed multilayer structure was numerically investigated using the Transfer Matrix Method (TMM) and Fresnel equations under TM-polarized light at 633 nm. Key performance parameters, including sensitivity, Full Width at Half Maximum (FWHM), Figure of Merit (FoM), Detection Accuracy (DA), Quality Factor (QF), and Limit of Detection (LoD), were systematically analyzed for HgII, PbII, ZnII, and binary ion mixtures. A 60 nm Al layer combined with a 23 nm TiO 2 coating provided a favorable balance between attenuation depth and resonance sharpness. Among the evaluated 2D materials, BP showed the most suitable response because of its low optical loss and narrow FWHM. The optimized B–sil/Al/TiO 2 /BP configuration achieved a maximum sensitivity of 512.47 °/RIU for HgII, while maintaining high sensitivity for PbII, ZnII, and binary mixtures, confirming its capability for trace-level detection. Electric field analysis revealed strong field localization at the TiO 2 /BP/analyte interface, enhancing light–matter interaction and sensing resolution. The proposed B–sil/Al/TiO 2 /BP SPR sensor demonstrated excellent optical performance, high sensitivity, and strong potential for real-time monitoring of heavy metal ions in aqueous environments.