Colorimetric determination of mercury(II) based on the inhibition of the aggregation of gold nanorods coated with 6-mercaptopurine

The authors describe an optical assay for determination of mercury(II) ion by making use of gold nanorods (AuNRs) which are found to aggregate after addition of 6-mercaptopurine (6-MP) by forming a covalent Au-S bond. Aggregation is accompanied by a color change to blue. However, the 6-MP induced aggregation is inhibited in the presence of Hg(II) results because of the formation of a more stable Hg-S bond. The different degrees of aggregation of the AuNRs is indicated by variations in the absorption spectra and accompanied by a color change from blue to brown. Under the optimal conditions, the ratio of absorbances at 780 and 665 nm varies in the 1-100 nM Hg(II) concentration range. The effect can also be detected with bare eyes. The limit of detection is 0.48 nM. The method is rapid, sensitive, and does not require sophisticated instrumentation. It was successfully applied to the determination of Hg(II) in spiked water samples.