A rapid and colorimetric biosensor based on GR-5 DNAzyme and self-replicating catalyzed hairpin assembly for lead detection

Abstract

A rapid and colorimetric biosensor for Pb²⁺ detection has been constructed on the basis of Pb²⁺-dependent GR-5 DNAzyme and the self-replicating catalyzed hairpin assembly (SRCHA) reaction. In the presence of Pb²⁺, the phosphodiester bond of the internal RNA base (rA) in GR-5 DNAzyme was cleaved by the enzyme strand and trigger DNA was released. Then the SRCHA reaction was initiated and the H1–H2 complex equipped with single-stranded DNA (ssDNA) sticky ends on both sides was formed. The sequences of the newly formed sticky ends on one side of H1–H2 were the same as that of trigger DNA and then additional CHA reaction cycles were initiated. Meanwhile, the intact G-quadruplex was reunited on the other side of H1–H2 for colorimetric signal readout. By taking advantage of the self-replication of trigger DNA, the response signal in this sensing system was significantly amplified and Pb²⁺ can be detected in a linear range from 20 to 100 nM with a detection limit of 2.6 nM within 20 min. In addition, this method can be applied to the reliable monitoring of spiked Pb²⁺ in environmental water and serum samples with satisfying results, providing a potential method for on-site and real-time detection of Pb²⁺ for environmental protection and related disease prevention.