Fluorescence Attenuation in a Triton X-114-Assisted Silver-Containing Nanosystem for Sensitive Determination of Mebendazole in Natural Waters

A solid-surface fluorescence method was developed for the determination of mebendazole (MBZ) in natural waters using a Triton X-114-assisted silver-containing nanosystem (Ag–TX-114) immobilized on filter paper. The nanosystem exhibited an excitation maximum at approximately 305 nm and an emission maximum at 376 nm. Increasing MBZ concentration produced a progressive decrease in fluorescence intensity. Under the selected conditions, 100 µL of 1.0 × 10−3 mol L−1 acetate buffer at pH 3.5 was used, and the filter-paper support was impregnated with the Ag–TX-114 suspension for 60 s. The method showed a linear response from 0.28 to 115 ng L−1, with detection and quantification limits of 0.08 and 0.28 ng L−1, respectively. Repeatability at 50 ng L−1 was 0.21% RSD (n = 7), and recoveries in natural-water samples ranged from 89.5 to 113.8%. Apparent MBZ concentrations measured in ten samples ranged from 6.12 to 50.12 ng L−1. The UV–Vis spectrum of MBZ showed an absorption band centered near 311 nm, indicating that a primary inner-filter effect may contribute to the observed fluorescence attenuation. The proposed method combines low sample and reagent consumption with direct solid-surface measurement and achieved an updated AGREE score of 0.65.