Highly sensitive chemiluminescent detection of lead ion based on its displacement of potassium in G-Quadruplex DNAzyme

Abstract

A simple and highly sensitive method for detecting lead ion (Pb²⁺) in biosamples was developed based on its displacement of potassium in G-Quadruplex DNAzyme, which can catalyze the luminol–H₂O₂ chemiluminescence (CL) reaction. By introducing a G-rich DNA sequence, PS2.M, which can fold into a G-quadruplex when binding with hemin in the presence of K⁺ and act as a superior horseradish peroxidase (HRP) mimicking-enzyme, we found this DNAzyme can effectively catalyze the H₂O₂-mediated oxidation of luminol, resulting in strong CL emission. The K⁺-stabilized G-quadruplex, upon the addition of Pb²⁺, is transformed into a Pb²⁺-stabilized G-quadruplex with higher stability but poor DNAzyme activity, sharply decreasing the CL readout signal. With this, a simple and sensitive detection method for Pb²⁺ in biosamples such as human hairs was developed with a linear range of 0.4–10 nM Pb²⁺ and a limit of detection (3σ) of 0.06 nM. Owing to the introduction of G-quadruplex DNAzyme, which was employed not only as a sensing unit but also as a catalyst in the chemiluminescent assay, this method holds great potential for clinical plumbism diagnosis by testing hair.