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

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 Hg²⁺ 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 × 10^-9 to 1 × 10^-6 M and 1 × 10^-8 to 3 × 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 A₆₄₀/A₅₂₀ and the concentration of AA in the range from 1 × 10^-8 to 1 × 10^-6 M with a detection limit of 4.8 nM (S/N = 3). Importantly, it has been successfully applied to determine Hg²⁺, Cd²⁺ in lake water and AA in vitamins C tablet.