Highly active G-quadruplex/hemin DNAzyme for sensitive colorimetric determination of lead(II)

A UV-vis, CD, and differential pulse voltammetric study was performed on the deactivation of the activity of parallel G-quadruplex/hemin DNAzymes (G4 DNAzymes) by Pb(II). The G4 DNAzyme carries a d[TC] sequence at its 3' end and is stabilized by potassium(I). On addition of Pb(II), the K(I) ions in the parallel G4 are replaced by Pb(II) to keep the parallel topology. Intruded Pb(II) decrease the affinity between the topology and hemin, this leads to a decrease of DNAzyme activity for catalyzing the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) by hydrogen peroxide to form a green dye with an absorption maximum at 420 nm. The assay does not use any amplification, and has a linear response in the 0.01 to 10 μM Pb(II) concentration range and a 7.1 nM limit of detection. The method was successfully applied to the analysis of spiked water samples. Graphical abstractSchematic diagram of the colorimetric lead(II) assay based on the competition between K⁺ and Pb²⁺ stabilized G-quadruplex/hemin DNAzymes (G4 DNAzymes).