Colorimetric response of lysine-caped gold/silver alloy nanocomposites for mercury(II) ion detection

[Display omitted] •Hg2+ determined by colorimetric assay using Au/Ag NCs as probe.•The aggregation degree of Au/Ag NCs was proportional to the concentration of Hg2+.•The absorbance ratio was used to quantify determination of Hg2+.•The proposed method is simple and sensitive. A simple and rapid colorimetric assay for determination of mercury(II) ion (Hg2+) in aqueous solutions was developed based on aggregation of gold/silver alloy nanocomposites (Au/Ag NCs). Au/Ag NCs were aggregated after the addition of Hg2+ and the positively charged amino acid, lysine. The different aggregation degrees of Au/Ag NCs is indicated by variations in the absorption spectra and accompanied by a color change from orange yellow to yellowish green. Under the optimal conditions, the shift of absorbance ratio (A650/A447) was proportional to Hg2+ concentrations in the range of 0.01–10.0 μM. The limit of detection is 4.8 nM. The proposed colorimetric assay was extremely specific for Hg2+ and other environmentally relevant metal ions did not interfere with the determination.