Development of a colorimetric probe for the semi-quantitative detection of mercury levels in water

Abstract

Mercury contamination is a significant public health and environmental problem. This work reports on the rational design of a novel colorimetric sensor based on 1.2-ethanedithiol modified gold nanoparticles for the selective recognition and visual detection of mercury (II) ions in aqueous solution. The functionalized nanoparticles characterized by visual inspection and UV–Vis spectroscopy. The detection approach has been linked to gold-sulphur-Hg2+-sulphur-gold interactions. These interactions have shown high selectivity towards Hg2+ with binding-induced red shift in the absorption spectra and showing no response to major interfering cations such as Zn2+, Cu2+, Pb2+, Ca2+, Ba2+, Sr2+, Na+, and NH4+ at 0.0001 M concentrations. Levels of 0.005 M were found to interfere greatly with Hg2+ in water using the proposed probe. The system responds well to Hg2+ at concentration as low as 0.002 mg/L as set by WHO and Standards Association of Zimbabwe (SAZ) as maximum permissible concentration limit. This approach provides a sensitive approach for the detection of Hg2+ based on a simple, rapid colour change at room temperature, and shows a great promise for point of use and in-field detection of toxic mercury in the environmental waters. The study also showed that the detection of Pb2+ can be done using the 1.2 ethanedithiol capped AuNPs with a unique green color change. The mechanism of detection of Hg2+ has been proposed.