A novel label-free and sensitive electrochemical biosensor for Hg²⁺ based on ligase-mediated formation of DNAzyme

A novel label-free electrochemical biosensor for the detection of Hg²⁺ based on ligase mediated creation of G-quadruplex-hemin DNAzyme has been developed. Firstly, Cp probe was immobilized on the gold electrode surface through Au-SH bond. In the presence of Hg²⁺, Cp and Ap probes were partly hybridized with the LJ probe respectively through the specific T-Hg²⁺-T interaction. Then, the adjacent 3'-OH terminal of Cp will link with the 5'-PO₄ terminal of Ap to form a G-rich DNA at the function of T4-ligase. After interaction with hemin, the G-rich DNA can form a G-quadruplex-hemin HRP-mimicking DNAzyme. Through measuring the current change caused by DNAzyme-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine(TMB), sensitive detection of Hg²⁺ can be achieved. The proposed sensor is simple, sensitive and selective, without the need of complicated labeling process, thus holds great potential for routine analysis of Hg²⁺ in environmental and biological samples.