Ultra trace mercury detection using a DNA aptamer sensor based on the electrochemical transformation of metal-organic frameworks

Mercury pollution has always been a concern due to its high toxicity and persistence. In this study, we designed an aptamer-based sensor relying on lanthanide metal-organic framework and in-situ generation of active substances through electrochemical conversion. Firstly, a lanthanide metal-organic framework with rod-shaped structure was successfully synthesized, which has higher conductivity and stability compared to traditional MOFs. By possessing the substantial specific surface area and profusion of active sites offered by rod-shaped Gd₄-MOF, gold nanoparticles (AuNPs) were deposited for the connection of tetrahedron DNA nanostructure (TDN). The active substances generated by electrochemical conversion has a more stringent arrangement and better response current compared to ordinary active substances, which can be used for ultra trace detection of mercury with higher sensitivity. After mercury added, DNA and mercury specifically bind to form thymine–Hg–thymine (T-Hg-T) structures, which cause changes in response current through conformational changes. The results demonstrated that a pronounced linear correlation between the DPV response and mercury concentration was observable, with a linear range of 1 fM to 200 fM and a detection limit of 0.66 fM. This sensor is successfully applied to detect the mercury content in marine products, so it has great application prospects for preventing and controlling mercury pollution.