Gold nanoparticles (AuNPs) modified by 8-hydroxy-quinoline (8-HQ) and stabilized by polyvinylpyrrolidone (PVP) were used for highly selective and sensitive colorimetric detection of Hg²⁺ based on the quick aggregation of AuNPs leading to a color change from wine red to gray. The limit of Hg²⁺ detection in real environmental water samples is 4.0 × 10⁻⁷ M by the naked eyes and 1.0 × 10⁻⁸ M by UV-vis spectroscopy.

In this work, we developed a colorimetric method for the detection of three kinds of ions with one kind of detection reagent. In detail, gold nanoparticles (Au NPs) multifunctionalized with 3-mercaptonicotinic acid and 4-aminobenzo-18-crown-6 (3-MPA-abc) were prepared and used as a colorimetric sensor for the simple and rapid detection of Ba²⁺, Cd²⁺ and Pb²⁺ ions. After adding Ba²⁺/Cd²⁺/Pb²⁺, the oxygen atom in the crown ether cavity and the carboxyl group of 3-mercaptopropionic acid can react with Ba²⁺/Cd²⁺/Pb²⁺ to form coordination bonds, resulting in the aggregation of the functionalized Au NPs and the color change of Au NP solution. The LOD of the colorimetric sensor for Ba²⁺/Cd²⁺/Pb²⁺ is 20 nM, 20 nM and 50 nM by the naked eye, respectively. A good linear relationship (R² = 0.9984, R² = 0.9917, R² = 0.9934) between the absorbance ratio and Ba²⁺/Cd²⁺/Pb²⁺ concentrations indicates that our Au NP based colorimetric sensor can be used for the quantitative assay of Ba²⁺/Cd²⁺/Pb²⁺, and this detection method was successfully applied in the detection of Ba²⁺/Cd²⁺/Pb²⁺ in real environmental samples.

A rapid, selective, visual detection sensor with high sensitivity and low detection limits for the pesticide pymetrozine (PYM) was prepared from melamine-modified gold nanoparticles (M-Au NPs), and shown to be effective in both natural water and food samples.

In this study, a new detection method for glyphosate (GPS) based on an anti-aggregation mechanism by using gold nanoparticles (AuNPs) is proposed. A certain amount of Pb²⁺ can cause the aggregation of AuNPs because of electrostatic interactions and the color of the solution changed from red to gray. However, in the presence of GPS, the above-mentioned process can be strongly hindered due to the chelation between GPS and Pb²⁺. Based on this anti-aggregation mechanism, the colorimetric detection method exhibits excellent sensitivity for GPS. The limit of detection (LOD) is 0.5 μM by the naked eye and 2.38 nM by UV-vis spectroscopy. The selectivity of the AuNP detection system for GPS is excellent compared with other pesticides. A good linear relationship (R² = 0.99695) between the absorption intensity ratio and GPS concentrations indicates that our probe can be used for the quantitative assay of GPS. The detection method has been successfully used for detecting GPS in real environmental samples.