Gold Nanoparticle-based Colorimetric Assay for Determination of Lead(II) in Aqueous Media

The authors presented a simple colorimetric assay for the detection of toxic heavy metal lead(II) ion(Pb2+). Pentapeptide, cysteine-alanine-leacine-asparagine-asparagine(CALNN), functionalized gold nanoparticles(GNPs) were aggregated in the presence of the divalent metal ion in solution by an ion-templated chelation process, which caused an easily measurable change in the absorption spectrum of the particles. Typically, mono-dispersing GNPs exhibit an absorption band at 522 nm, corresponding to a red color solution, while aggregated GNPs have it at longer wavelengths, corresponding to a purple or blue color solution. The chelation/aggregation process is reversible via the addition of a strong metal ion chelator such as EDTA. Highly selective and sensitive detection of Pb2+ in aqueous solution is thus provided. A detection limit of 0.1 mu mol/L of Pb2+ was demonstrated.