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 (R-2 = 0.9984, R-2 = 0.9917, R-2 = 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.