Functionalization of silver nanoparticles with glutamine and histidine for simple and selective detection of Hg2+ ion in water samples

Abstract

A simple, rapid and sensitive colorimetric method was developed for the detection of Hg2+ion in water samples using glutamine (Gln) and histidine (His) functionalized silver nanoparticles (Gln-His-Ag NPs) as a probe. The functionalized Ag NPs were confirmed by UV–vis, FT-IR and transmission electron microscopic (TEM) techniques, respectively. The Hg2+ion was induced quickly the aggregation of Gln-His-Ag NPs, yielding a color change from yellow to orange, which can be readily seen by naked eye. The recognition mechanism is attributed to unique supramolecular nanostructures of Gln-His-Ag NPs, which yields strong interaction (cooperative metal-ligand interaction) between Gln-His-Ag NPs and Hg2+ion. A linear correlation was obtained in the range of 100–1000 μM with a detection limit of 25.48 μM. However, the sensitivity of the probe was greatly improved by the addition of 0.2 M NaCl as an ionic strength. The calibration graph was constructed between absorption ratio (A500/A402) and concentration of Hg2+ion in the range of 1.0–500 μM with the detection limit of 0.90 μM, which is 28-times lower than the direct method (without NaCl). This method was successfully applied to detect Hg2+ion in water samples. With the advantages of simplicity, selectivity and low sample volume, this method can potentially suitable for on-site monitoring of Hg2+ion.