Direct colorimetric biosensing of mercury(II) ion based on aggregation of poly-(γ-glutamic acid)-functionalized gold nanoparticles

•The colorimetric probe for Hg2+ has been developed by using a PGA-AuNPs system.•The PGA could interact with Hg2+ from the PGA-Hg-PGA to induced aggregation of AuNPs.•The assays could be achieved with the naked eye.•This approach shows high selectivity for Hg2+ over other transition metal.•This method was applied to the determination of Hg2+ in real water samples.

A simple and sensitive method for colorimetric detection of mercury ion (Hg2+) has been developed by using a poly (γ-glutamic acid) functionalized gold nanoparticles (PGA-AuNPs) system. Electrostatic self-assembly technique was used to assemble negatively charged PGA on the surface of positively charged CTAB-capped AuNPs. With the increase of Hg2+ concentration, the color of the solution would progress from light red to purple blue. The results showed that the absorbance ratio (A750/A580) was linear with the Hg2+ concentration in the range of 0.01–10 μM and from 50 to 300 μM, with the correlation coefficients of 0.998 and 0.991, respectively. The reported probe is suitable for real-time detection of Hg2+ in water with the limit of detection (LOD) of 1.9 nM obtained by UV–vis spectrum, and exhibits selectivity toward one order of magnitude over other metal ions. This approach was applied successfully to the determination of Hg2+ in tap water and mineral water, and the recoveries were from 90% to 103% and from 103.53% to 113%, respectively. The proposed method is rapid, low-cost and free of complex equipment, making it possible to analyze Hg2+ in various water samples.

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