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

• An amplified colorimetric method for the detection of Hg2+ is proposed.
• The method based on the combination of T–Hg2+–T base pairs and hybridization chain reaction.
• This “turn-on” sensing system enables the high sensitive and selective detection of Hg2+.
• The method's detection limit is 3 orders of magnitudes lower than the MAL defined by EPA.
• In this sensing system, no labeled oligonucleotides and expensive instruments are required.

An amplified colorimetric detection of Hg2+ is proposed by combining T–Hg2+–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 Hg2+, one of the hairpins is opened by an assistant probe with the help of T–Hg2+–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 ABTS2− 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 Hg2+ with a detection limit of 9.7 pM.