Strategy for the detection of mercury ions by using exonuclease III-aided target recycling

Herein, a simple, highly sensitive and selective exonuclease III (Exo III)-based sensor was developed for mercury ions Hg2+ detection without the need of complicated, high-cost and time-consuming labeling. In this strategy, two oligonucleotides were employed for the experiment design. DNA1 was prepared with one DNA strand which was designed as a quadruplex-forming oligomer, and which was constructed as 3'-protruding to ensure the probe cannot be digested by Exo III. When the target Hg2+ is introduced into the sensing system, it associates with DNA1 and DNA2 to form double strand DNAs (DNA1/DNA2 duplexes) which have a blunt 3'-terminus. Exo III then can degrade part of DNA1, releasing the DNA1 and Hg2+, and ultimately liberating the G-rich oligomer. This released G-rich oligomer folds into a G-quadruplex structure and thus allows the formation of DNAzyme in the presence of hemin. The formed DNAzyme can effectively catalyze the H2O2-mediated oxidation of ABTS, giving rise to a change in solution color. The released DNA1 and Hg2+ are free to bind to another 3'-protruding terminus of DNA1 to trigger a new digestion reaction, leading to significant amplification of the signal. The present new strategy shows a limit of detection as low as 66 pM and excellent selectivity toward Hg2+ over a wide range of metal ions.