Highly Selective Colorimetric Assay of Cu2+ Ions by Silver Nanoparticles Conjugated with 1-(2-Mercaptoethyl)-1,3,5-triazinane-2,4,6-trione

A simple and sensitive colorimetric assay method for the determination of Cu2+ ions in aqueous samples was developed using silver nanoparticles functionalized with 1-(2-mercaptoethyl)-1,3,5-triazinane-2,4,6-trione (MTT-AgNPs). The Cu2+ ion appears to play the role of the metal center of the coordination complex, which can form N-Cu2+-O coordination bonds with the MTT-AgNPs, shorten their interparticle distance, and induce aggregation of the MTT-AgNPs. The binding site and sensing mechanism of Cu2+ to MTT-AgNPs were characterized by XPS and FT-IR spectroscopy. This aggregation results in a dramatic color change from yellow to dark red. Therefore, the concentration of Cu2+ ions in environmental samples can be quantitatively detected by the naked eye or by UV-Vis spectrometry when using the MTT-AgNP sensor. The sensitivity of the detection is significantly improved by modulating the solution to pH 9, leading to a more rapid color change in the optimized AgNP system. The absorption ratios (A(555)/A(395)) of the modified AgNP solution exhibited a linear correlation with the Cu2+ ion concentrations, with a limit of detection of 15.2 nM. This cost-effective detection system allows for the rapid and facile determination of the concentration of Cu2+ ions in aqueous samples.