A Label-free Simple Biosensor for Pb²⁺ Detection Based on G-quadruplex DNA and Exonuclease III

Lead ions (Pb²⁺), as heavy metal ions, pose significant hazards to human health. Therefore, it is of great significance to establish a simple and effective method for detecting Pb²⁺. In this study, a label-free Pb²⁺ biosensor was established based on G-quadruplex DNA (G4-DNA) and Exonuclease III (Exo III). In the absence of Pb²⁺, the double-stranded DNA formed by G4-DNA and its complementary strand can be cleaved by Exo III. When Pb²⁺ was present, G4-DNA can form a cage-like structure with the assistance of Pb²⁺, thereby disrupting the formation of double-stranded structures and blocking the cleavage of DNA by Exo III. Subsequently, the fluorescence signal was released upon the addition of the DNA dye (SG I). This biosensor possessed a broad linear detection range of 10 nM - 20 µM and a low limit of detection (LOD) of 7.3 nM. Moreover, the proposed biosensor exhibited excellent specificity for Pb²⁺ and achieved satisfactory recovery rates (91.4%-109.7%) in pond water.