A simple strategy for the visual detection and discrimination of Hg2+ and CH3Hg+ species using fluorescent nanoaggregates.

Fluorescent nanoaggregates (FNAs) based on phenanthroline-based amphiphiles show changes in solution color from colorless to yellow upon addition of both Hg2+ (LOD ∼4 ppb) and CH3Hg+ (LOD ∼18 ppb). However, the extent of fluorescence quenching is more prominent with Hg2+ (∼12 fold) than with CH3Hg+ (∼4 fold). Also, unlike Hg2+, the interaction of CH3Hg+ needs more time, ∼10 min at room temperature. Experimental evidence indicates that both mercury species coordinate with the phenanthroline unit and facilitate the charge transfer interaction while destabilizing the nanoassembly. The lower charge density on CH3Hg+ along with its large size compared to Hg2+ may be the reason for such observations. Interestingly, FNAs show a selective response towards CH3Hg+ when pre-treated with EDTA. Further, analysis of heavy metal pollutants in drinking water and biological samples was performed. High recovery values ranging from 96% to 103.0% were estimated along with relatively small standard deviations (<3%). Low-cost, reusable test strips were designed for rapid, on-site detection of mercury species. Further, the in situ formed metal complexes are allowed to interact with thiol-containing amino acids. As expected, CH3Hg+, being less thiophillic, endures less interaction with cysteine. Mechanistic investigations indicate that thiolated amino acids can bind with the metal ion center and form a tertiary complex (cooperative interaction).