Colorimetric Assay for Lead Ions Based on the Leaching of Gold Nanoparticles

A colorimetric, label-free, and nonaggregation-based gold nanoparticles (Au NPs) probe has been developed for the detection of Pb2+ in aqueous solution, based on the fact that Pb2+ ions accelerate the leaching rate of Au NPs by thiosulfate (S2O3 2−) and 2-mercaptoethanol (2-ME). Au NPs reacted with S2O3 2− ions in solution to form Au(S2O3)2 3− complexes on the Au NP surfaces, leading to slight decreases in their surface plasmon resonance (SPR) absorption. Surface-assisted laser desorption/ionization time-of-flight ionization mass spectrometry (SALDI-TOF MS) data reveals the formation of Pb−Au alloys on the surfaces of the Au NPs in the presence of Pb2+ ions and 2-ME. The formation of Pb−Au alloys accelerated the Au NPs rapidly dissolved into solution, leading to dramatic decreases in the SPR absorption. The 2-ME/S2O3 2−-Au NP probe is highly sensitive (LOD = 0.5 nM) and selective (by at least 1000-fold over other metal ions) toward Pb2+ ions, with a linear detection range (2.5 nM−10 μM) over nearly 4 orders of magnitude. The cost-effective probe allows rapid and simple determination of the concentrations of Pb2+ ions in environmental samples (Montana soil and river), with results showing its great practicality for the detection of lead in real samples.