Amplified colorimetric detection of mercuric ions through autonomous assembly of G-quadruplex DNAzyme nanowires.

An amplified colorimetric detection of Hg(2+) is proposed by combining T-Hg(2+)-T base pairs and hybridization chain reaction (HCR). Two hairpins consisting of three-fourths and one-fourth of the horseradish peroxidase (HRP)-mimicking DNAzyme in inactive configuration are used as functional elements. In the presence of Hg(2+), one of the hairpins is opened by an assistant probe with the help of T-Hg(2+)-T base pairs and this triggers an autonomous cross-opening of the two hairpins using the strand displacement principle, resulting in the formation of DNA nanowires consisting of numerous reunited Q-quadruplex DNAzyme units. The resulting catalytically active hemin/G-quadruplex HRP-mimicking DNAzymes catalyze the oxidation of ABTS(2-) by H2O2 into a green-colored cationic radical ABTS(•+) for the colorimetric readout. This "turn-on" sensing system enables the high sensitive and selective detection of aqueous Hg(2+) with a detection limit of 9.7 pM.