High-Performance Colorimetric Detection of Thiosulfate by Using Silver Nanoparticles for Smartphone-Based Analysis

Developing thiosulfate (S₂O₃^2-) sensors with silver nanoparticles (AgNPs) for analysis of aqueous solutions with the interference of other anions remains challenging. In this study, we propose a new strategy for excellent selective colorimetric detection of S₂O₃^2-. The nonmorphological transition of AgNPs leading to a color change from yellow to brown is verified by UV-vis, TEM, DLS, SEM, and XPS analyses. The sensor exhibits high sensitivity with detection limits of 1.0 μM by naked-eye determination and 0.2 μM by UV-vis spectroscopy analysis. The linear relationship (R² = 0.998) between the (A₀ - A)/A₀ values and S₂O₃^2- concentrations from 0.2 μM to 2.0 μM indicates that the fabricated AgNPs-based colorimetric sensor can be employed for quantitative assay of S₂O₃^2-. Colorimetric responses are also monitored using the built-in camera of a smartphone. The sensor shows a linear response to S₂O₃^2- in 0-20.0 μM solutions under the optimized conditions and is thus more suitable for rapid on-site tests than other detection methods. A smartphone application (app) is downloaded under Android or IOS platforms to measure the RGB (red, green, blue) values of the colorimetric sensor after exposure to the analyte. Following data processing, the RGB values are converted into concentration values by using preloaded calibration curves. Confirmatory analysis indicates that the proposed S₂O₃^2- colorimetric sensor exhibits feasibility and sensitivity for S₂O₃^2- detection in real environmental samples.