Aptamer-functionalized gold nanoparticles for mercury ion detection in a colorimetric assay based on color change time as signal readout

A universal strategy for a rapid colorimetric method for Hg 2+ in an aqueous solution is described. The specific binding of Hg 2+ (thymine-Hg 2+ -thymine) with thiolated DNA-functionalized gold nanoparticles (AuNPs) via Au–S bonds increases the spatial hindrance of the AuNP surface, resulting in a weakened catalytic ability of AuNPs to catalyze the reaction between p-nitrophenol and NaBH 4 . Therefore, the color change time (CCT) of the solution from yellow to colorless becomes longer. Based on the kinetic curve of absorbance over time measured by a UV spectrometer, the level of Hg 2+ in aqueous solutions can be easily quantified. A linear relationship between CCT and Hg 2+ concentration was obtained in the 10–600-nM range with a detection limit of 0.20 nM, which is much lower than the limit value (10 nM) defined by the US Environmental Protection Agency for Hg 2+ in drinking water. The excellent sensitivity comes from CCT as the signal output of the probe, rather than the absorbance or wavelength change used in traditional colorimetric probes as the signal output. Graphical Abstract