Eco-friendly colorimetric detection of lead and mercury using <scp>l</scp> -cysteine-functionalized gold nanoparticles: a step towards greening the exposome

Heavy metal toxicity, particularly from lead (Pb) and mercury (Hg), poses a significant threat to the biological system and the exposome, even at trace levels. In alignment with the 'Greening the Exposome' initiative, this study presents an eco-friendly and rapid colorimetric technique for detecting Pb and Hg in water. This method utilizes biogenic l-cysteine functionalized gold nanoparticles (AuNPs) of varying sizes as a colorimetric sensor, offering selective detection of these heavy metals. The utilization of l-cysteine, a naturally occurring amino acid, enhances the sustainability of the assay. The l-cysteine functionalized AuNPs demonstrate selectivity towards Pb and Hg through visually observable color changes, directly correlated with shifts in the surface plasmon resonance (SPR). The characteristic SPR peak of AuNPs, initially observed around 525 nm, undergoes a red shift upon aggregation in the presence of Pb and Hg, resulting in peaks at approximately 725 nm for Pb and 700 nm for Hg. The calibration curve shows a linearity range of 100-500 ppb for determination of Pb and Hg with a limit of detection of 290 ppb and 140.35 ppb. This simple, cost-effective, and environmentally conscious approach offers a promising tool for monitoring heavy metal contamination in aqueous environments, contributing to a better understanding and management of the chemical exposome.