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

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.