Novel colorimetric sensor based on peroxidase-like activity of chitosan-stabilized Au/Pt nanoclusters for trace lead

Abstract

In this study we propose a new colorimetric sensor for trace lead ions in milk samples. Au/Pt nanoclusters were synthesized using chitosan as the stabilizer at room temperature. Chitosan-protected Au/Pt nanoclusters exhibit strong peroxidase-like activity, and could catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the vicinity of hydrogen peroxide (H₂O₂) and create a visual blue color. The detection mechanism is based on the Pb²⁺ ions-induced aggregation of chitosan–Au/Pt NCs that causes changes in size and impairs the enzymatic performance of Au/Pt NCs. Experiments indicated that a step-by-step increase in concentration of Pb²⁺ ions gradually decreased peroxidase activity and this reduction was linear. Based on the declared procedure, a colorimetric detection for Pb²⁺ was obtained with a detection limit (LOD) of 16 nM and a linear range from 25 nM to 1 μM. The method was considerably selective toward Pb²⁺ over other metal ions. Low price and simplicity support the application of sensing Pb²⁺ in milk samples.