Highly selective, colorimetric detection of Hg2+ based on three color changes of AuNPs solution from red through sandy beige to celandine green

Abstract A new colorimetric method of detecting Hg 2+ in aqueous solutions was proposed, based on the three color changes of gold nanoparticles (AuNPs) with the assistance of ascorbic acid (AA) and multi-sulfhydryl functionalized hyperbranched polyethylenimine (SH-HPEI). The mechanism of sensing is based on the formation of Au-Hg alloy and its aggregation, along with the corresponding three color changes from red (AuNPs) through sandy beige (Au-Hg alloy) to celandine green (larger Au-Hg alloy). Compared with usual colorimetric assays with only one color change progress from red to blue or red to purple of reported AuNPs, this assay is highly selective for Hg 2+ detection due to the fact that the appearing probability of identical three color changes triggered by interfering agents or the possibility of false positive results is very, very low. The detection limit of 8.76 × 10 −9  M is lower than the guideline value of Hg 2+ (30 nM) in drinking water defined by the World Health Organization (WHO). Meanwhile, the concentration range (from 8.76 × 10 −9 to 1.27 × 10 −4  M) of this new detection method is the widest one that has been reported. Moreover, this method is successfully applied to detecting Hg 2+ in real water sample. More importantly, this novel colorimetric sensor based on multiple color changes may open a new avenue for the development of Hg 2+ sensing probes.