Colorimetric determination of Pb 2+ ions based on surface leaching of Au@Pt nanoparticles as peroxidase mimic.

We report the first use of metallic nanozyme as colorimetric probe for Pb ²⁺ determination. The method is based on the surface leaching of Au@PtNP nanozyme by Pb ²⁺ -S ₂ O ₃ ^2- ions, accompanied by a decreased catalytic activity of the metallic nanozyme. To construct this colorimetric determination, the Pt deposition onto the AuNPs was carefully investigated and other experimental factors including kind of substrate and buffer were optimized. With increasing Pb ²⁺ concentration, the catalytic activity of the Au@PtNPs decreased gradually. As a result, the blue color at 650 nm from the oxidation of 3,3',5,5'-tetramethylbenzidine by H ₂ O ₂ faded gradually. A determination limit of 3.0 nM Pb ²⁺ with a linear range from 20 to 800 nM was obtained. The assay demonstrated negligible response to common metal ions even at elevated concentrations. This colorimetric method was applied to the determination of Pb ²⁺ ions spiked in lake water samples, and good recoveries (96.8-105.2%) were obtained. The above results indicate the potential application of metallic nanozymes in developing robust colorimetric assays. Graphical abstract Schematic representation of the surface leaching of Au@PtNP nanozyme by Pb ²⁺ -S ₂ O ₃ ^2- ions, accompanying the decreased catalytic activity of the metallic nanozyme.