Label-free colorimetric detection of Hg2+ based on Hg2+-triggered exonuclease III-assisted target recycling and DNAzyme amplification

This work reported a label-free colorimetric assay for sensitive detection of Hg 2+ based on Hg 2+ -triggered hairpin DNA probe (H-DNA) termini-binding and exonuclease Ш (Exo Ш)-assisted target recycling, as well as hemin/G-quadruplex (DNAzyme) signal amplification . The specific binding of free Hg 2+ with the thymine–thymine (T–T) mismatches termini of H-DNA could immediately trigger the Exo Ш digestion, and then set free G-quadruplex segments and Hg 2+ . The Exo Ш impellent recycling of ultratrace Hg 2+ produced numerous G-quadruplexes. The corresponding DNAzymes catalyzed efficiently the H 2 O 2 -mediated oxidation of the ABTS 2− to the colored product in the presence of hemin . Using the color change as the output signal, and the Exo Ш-aided Hg 2+ recycling and DNAzyme as the signal amplifier, the ultrasensitive assay system successfully achieved visual detection of Hg 2+ as low as 1.0   nM by the naked eye, and was suitable for field monitoring. The calibration curve was linear in the range of 50.0   pM to 20.0   nM for Hg 2+ ( R =0.9962) with a detection limit of 10.0   pM. Moreover, this proposed strategy showed excellent selectivity , portability and low-cost, and was successfully applied to colorimetric detection of Hg 2+ in laboratory tap water and Jialing river water samples.