Colorimetric and visual determination of Au(III) ions using PEGylated gold nanoparticles

A highly selective method is described for the colorimetric determination of Au(III) ions in acidic solution using gold nanoparticles (AuNPs) functionalized with thiolated methoxy poly(ethylene glycol) (mPEG). The presence of Au(III) induces the aggregation of the PEG-AuNPs, and this is accompanied by a color change from wine red to blue, and a decrease in absorbance at 525 nm. This can be monitored spectrophotometrically and visually. Absorbance at 525 nm linearly drops in the 0.50 to 1.75 mg.L-1 Au(III) concentration range, with a 0.25 mg.L-1 detection limit. The method is surprisingly selective over other metal ions. It was successfully applied to the analysis of ore samples.