Lead(II)-Induced Allosteric G-Quadruplex DNAzyme as a Colorimetric and Chemiluminescence Sensor for Highly Sensitive and Selective Pb2+ Detection

The lead ion (Pb(2+)) has been proven to induce a conformational change of K(+)-stabilized G-quadruplex DNAzyme and inhibit the peroxidase-like activity [Li, T.; Wang, E.; Dong, S. J. Am. Chem. Soc. 2009, 131, 15082-15083]. This provides a rationale for utilizing Pb(2+)-induced allosteric G-quadruplex DNAzyme to probe aqueous Pb(2+). Here, we choose a common G-quadruplex DNAzyme named PS2.M to develop a novel Pb(2+) sensor with two detection means: colorimetry and chemiluminescence (CL). In the presence of K(+), PS2.M (with hemin as a cofactor) exhibits a superior DNAzyme activity and effectively catalyzes the H(2)O(2)-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) or luminol, which results in a color change or generates CL emission. Upon the addition of Pb(2+), K(+)-stabilized PS2.M is induced to convert to the Pb(2+)-stabilized structure with higher stability but lower DNAzyme activity, which is reflected by an obvious increase in DNA melting temperature but a sharp decrease in readout signal. This allows us to utilize PS2.M for quantitative analysis of aqueous Pb(2+) using the ABTS-H(2)O(2) colorimetric system and luminol-H(2)O(2) CL system. In each case, the readout signal is linearly dependent on the logarithm of Pb(2+) concentration within a certain range. Nevertheless, two sensing systems provide different sensitivity for Pb(2+) analysis. With colorimetry, Pb(2+) can be detected at a level of 32 nM (approximately 7 ppb), whereas the detection limit of Pb(2+) is 1 nM (0.2 ppb) when utilizing the CL method. In addition to high sensitivity, the above sensing systems exhibit good selectivity for Pb(2+) over other metal ions. These results demonstrate the facility and effectivity of our introduced DNAzyme-based sensor for quantitative Pb(2+) analysis.