Colorimetric sensing of lead ion using gold nanorod with enhanced sensitivity via catalytic etching

Lead, a prevalent heavy metal, poses significant risks to human health through various exposure pathways. Herein, we propose an extremely sensitive assay toward lead ion (Pb²⁺) using gold nanorods (GNRs) as probes based on its catalytic activity on etching gold in the presence of 2-mercaptoethanol and sodium thiosulfate. In the presence of Pb²⁺, etching predominantly occurs at the two ends of GNRs, leading to the reduction of aspect ratio and the corresponding blueshift of the localized surface plasmon resonance (LSPR). With increasing Pb²⁺ concentration over the range of 0–50 μM, the color of GNR solution lightens, ultimately becoming colorless. The wavelength shift (Δλ) of LSPR is highly dependent on Pb²⁺ concentration, with a linear regression equation of Δλ = 10.05ln[Pb²⁺] + 9.59 and an R² = 0.995. The assay demonstrates high selectivity for Pb²⁺ over other potentially interfering ions such as Cu²⁺ because of its special catalytic activity in the etching of GNRs and the complexing ability of 2-mercaptoethanol and sodium thiosulfate. Validation of the assay was accomplished by analyzing several forest-derived food samples, affirming the accuracy in real-world scenarios. The assay we developed holds promise for many applications in environmental protection and food safety.