A Self-Assembled G-Quadruplex/Hemin DNAzyme-Driven DNA Walker Strategy for Sensitive and Rapid Detection of Lead Ions Based on Rolling Circle Amplification

Herein, a sensitive biosensor is constructed based on a novel rolling circle amplification (RCA) for colorimetric quantification of lead ion (Pb2+). At the detection system, GR5 DNAzymes are modified on the surface of an immunomagnetic bead, and Pb2+ is captured by the aptamer, inducing the disintegration of the GR5 DNAzyme and the release of the DNA walker. After the introduction of the template DNA, T4 DNA ligase, and phi29 DNA polymerase, an RCA is initiated for the sensitivity improvement of this method. Moreover, a G4-hemin DNAzyme is formed as a colorimetric signal, owing to its peroxide-like activity to catalyze the TMB-H2O2 substrate. Under the optimized conditions, the limit of detection (LOD) of this fabricated biosensor could reach 3.3 pM for Pb2+ with a concentration in the range of 0.01-1000 nM. Furthermore, the results of real samples analysis demonstrate its satisfactory accuracy, implying its great potential in the rapid detection of heavy metals in the environment.