Conformation-Dependent Exonuclease III Activity Mediated by Metal Ions Reshuffling on Thymine-Rich DNA Duplexes for an Ultrasensitive Electrochemical Method for Hg2+ Detection

Hg2+ is known to bind very strongly with TT mismatches in DNA duplexes to form THg2+T base pairs, the structure of which is stabilized by covalent NHg bonds and exhibits bonding strength higher than hydrogen bonds. In this work, we exploit exonuclease III (Exo III) activity on DNA hybrids containing THg2+T base pairs and our experiments show that Hg2+ ions could intentionally trigger the activity of Exo III toward a designed thymine-rich DNA oligonucleotide (e-T-rich probe) by the conformational change of the probe. Our sensing strategy utilizes this conformation-dependent activity of Exo III, which is controlled through the cyclical shuffling of Hg2+ ions between the solution phase and the solid DNA hybrid. This interesting attribute has led to the development of an ultrasensitive detection platform for Hg2+ ions with a detection limit of 0.2 nM and a total assay time within minutes. This simple detection strategy could be used for the detection of other metal ions which exhibit specific interactions with natural or synthetic bases.