Hg2+-triggered exonuclease III-assisted dual-cycle targets recycling amplification for label-free and ultrasensitive colorimetric detection of Hg2+

A label-free dual-cycle targets recycling strategy is firstly proposed for ultrasensitive detection of Hg2+ based on the Hg2+-triggered toehold binding, exonuclease III-assisted dual-cycle targets recycling signal amplification and hemin/G-quadruplex (DNAzyme) signal amplification. In the presence of Hg2+, the matched hybridization of Hg2+ discrimination probe and the duplex DNA probe by T-Hg2+-T coordination triggers the Exo III-assisted DNA cleavages that release Hg2+, Hg2+ discrimination probe, G-quadruplex forming DNA probe and a new target DNA fragment (I-region). The released Hg2+ (cycle 1) and the new target DNA (cycle 2) are recycled. The Exo III-assisted dual-cycle targets recycling amplification triggered by ultratrace amounts of Hg2+ produces numerous quadruplex-forming sequences that bind hemin to yield G-quadruplex-hemin DNAzymes, which efficiently catalyze the H2O2-mediated oxidation of the ABTS(2-)to the colored products. This method exhibits a high sensitivity toward Hg2* with a detection limit of 0.05 pmol/L, and the calibration curve is linear in the range of 0.05 pmol/L to 100 pmol/L (R-2 = 0.9905). This proposed strategy displayed excellent sensitivity, simplicity, low-cost and remarkable specificity, and was successfully implemented for colorimetric detection of Hg2+ in tap water, lake water and Xiangjiang River water samples with good recovery and accuracy. (C) 2017 Elsevier B.V. All rights reserved.