Exonuclease III‑assisted and target-induced conformational change of DNA hairpins for electrochemical detection of mercury (II)

Here, we report a DNA hairpin strategy for electrochemical determination of Hg 2+ based on T-Hg 2+ -T pairs and exonuclease III (Exo III) assistance. The innovation of this work lies in the designed DNA structure and detection principles. Unlike the previously reported DNA hairpin structure, the ring portion of the hairpin DNA we designed consisting of T bases serves as a recognition probe, forming a T-Hg-T complex with Hg 2+ . The stem is composed of 5 pairs of complementary bases, which is conducive to the stability of the hairpin structure. After the formation of T-Hg-T in the ring, with the help of Exo III, Exo III can digest more DNA than the T bases designed in the stem. In this event, the shorter the length of the remaining DNA strand on the electrode, the weaker the repulsive force against [Fe(CN) 6 ] 3−/4− , and the stronger the differential pulse voltammetry (DPV) current signal, achieving “signal-on” transitions. Under the optimal conditions, the DPV current response increases with increasing Hg 2+ concentration and is linear with the logarithm of Hg 2+ concentration (1 nM–10 μM). The limit ofdetection is 0.16 nM. The electrochemical sensor was successfully applied to the determination of Hg 2+ in river water.