Colorimetric sensing of mercury (II) ion based on anti-aggregation of gold nanoparticles in the presence of hexadecyl trimethyl ammonium bromide

A new specific and sensitive colorimetric sensor based on anti-aggregation of unmodified gold nanoparticles (AuNPs) for mercury ion detection was studied by forming Au-Hg alloys deposited onto the surface of AuNPs. In the protocol, hexadecyl trimethyl ammonium bromide (CTAB) could cause the aggregation of AuNPs and induced the color change from red to blue due to the strong electrostatic attraction between CTAB and citrate ion capped gold nanoparticles. In the presence of Hg²⁺, citrate ion capped AuNPs reduced Hg²⁺ to Hg and then formed Hg-Au alloys, which could inhibit the aggregation of AuNPs caused by CTAB to some extent. Based on these findings, Hg²⁺ was detected by a blue-to-red color change of AuNPs solution containing CTAB. Also, the limit of detection (LOD) was 11.9 nM by UV–vis spectroscopy, which was lower than the guideline concentration of Hg²⁺ (30 nM) in drinking water set by the World Health Organization (WHO). And the results showed the absorbance ratios A₆₅₀/A₅₂₀ had a good linear correlation with the Hg²⁺ concentration from 0 to 680 nM, which could be used for the quantitative detection of Hg²⁺. This method was successfully used to detect Hg²⁺ in tap water sample.