Colorimetric and Label-Free Optical Detection of Pb2+ Ions via Colloidal Gold Nanoparticles

The detection of Lead (Pb) heavy metal in water is crucial in many chemical processes as it is associated with serious health hazard. Here, we report the selective and precise colorimetric detection of Pb2+ ions in water exploiting the mechanisms of aggregation and self-assembly of Glutathione (GSH) functionalized gold nanoparticles (GNPs). The carboxyl functional groups are available to create coordination complexes with Pb2+ inducing aggregation amongst the GSH-GNPs in the presence of Pb2+ due to the chelation of the GSH ligands. The resulting aggregation of amongst the GSHGNPs in the presence of Pb2+ increases the aggregate size depending on available Pb2+ ions affecting the plasmonic coupling. This causes in a substantial shift in the plasmon wavelength to a longer wavelength side with increasing Pb2+ concentration, resulting in a red-to-blue colorimetric or visual change, enabling instant determination of lead content in water.