A Simulation-Based Study of a Black Phosphorus-Based Complex Multilayer SPR-Based Optical Sensor for Wastewater Monitoring

Abstract

The increasing global threat of water pollution demands advanced multilayer sensing technologies with efficacy to detect contaminants with high sensitivity and adaptability in complex aquatic environments. In this theoretical analysis, we investigated a novel multilayer surface plasmon resonance (SPR) system as an optical sensing platform to detect water pollutants and salinity concentrations. The proposed sensor comprised silver, barium borate (BBO), and black phosphorus (BP) layers on a Borokon 7 (BK7) prism, which formed a tunable and highly responsive configuration under the Kretschmann geometry. It employed the transfer matrix method (TMM) and angular interrogation in the visible regime to evaluate reflectance spectra and key sensing parameters. The outcomes revealed that the sensor exhibited high sensitivity and selectivity for refractive index (RI) variations corresponding to polluted water samples, including sodium chloride (NaCl) concentrations. The system exhibited strong plasmonic coupling and interfacial interactions, yielding the maximum sensitivity (138.7°/RIU) and figure of merit (73.57 RIU⁻¹) toward water samples with 4% NaCl and chemical contamination, respectively. At refractive index of 1.33 and 1.34, by varying the layers of BBO and BP, the maximum sensitivity achieved was 320°/RIU with six BBO layers and a monolayer of BP. These results demonstrated that the proposed SPR sensor configuration, which successfully differentiated between various water quality levels based on refractive index variations, had tremendous potential for next-generation real-time water quality monitoring.