Colorimetric detection of Ba²⁺, Cd²⁺ and Pb²⁺ based on a multifunctionalized Au NP sensor

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.