A highly sensitive colorimetric probe for Cd2+, Hg2+ and ascorbic acid determination based on trithiocyanuric acid-AuNPs

A highly sensitive and selective colorimetric assay is proposed for the detection of mercury ions (Hg2+), cadmium ions (Cd2+) and ascorbic acid (AA) using trithiocyanuric acid (TMT) functionalized gold nanoparticles (TMT-AuNPs). TMT-AuNPs are dispersed in 40 mM NaCl solution, while the presence of Hg(2+)and Cd2+ can induce TMT-AuNPs aggregate due to the strong interaction of Hg2+ and Cd2+ with TMT. Then the quantitative detection of Hg2+ and Cd2+ can be realized in the linear range from 5 x 10(-9) to 1 x 10(-6) M and 1 x 10(-8) to 3 x 10(-7) M, with a lower detection limit of 2.8 nM for Hg2+ and 3.5 nM for Cd2+ (S/N = 3), respectively. To distinguish Hg2+ from Cd2+, a reductive biological small molecule ascorbic acid (AA) was used based on the different redox interaction of AA with Hg2+ and Cd2+. When the mixture of AA and Hg2+ was added into TMT-AuNPs solution, the state of TMT-AuNPs was still dispersed because Hg2+ was reduced by AA. On the contrary, when the mixture of AA and Cd2+ was added into TMT-AuNPs solution, the TMT-AuNPs was aggregated and the color of the solution has no obvious change compared to the system of Cd2+-TMT-AuNPs since the weak interaction between AA and Cd2+. Thus, AA could be detected. A linear correlation exists between the ratio of A(640)/A(520) and the concentration of AA in the range from 1 x 10(-8) to 1 x 10(-6) M with a detection limit of 4.8 nM (S/N = 3). Importantly, it has been successfully applied to determine Hg2+, Cd(2+ )in lake water and AA in vitamins C tablet.