Target-inspired Pb2+-dependent DNAzyme for ultrasensitive electrochemical sensor based on MoS2-AuPt nanocomposites and hemin/G-quadruplex DNAzyme as signal amplifier

Abstract In this work, a novel Pb2+ electrochemical DNAzyme sensor was developed for ultrasensitive detection of lead ions (Pb2+) in water environment by coupling with the MoS2–AuPt nanomaterials and hemin/G-quadruplex DNAzyme, which acting as the electrocatalytic signal tag. Streptavidin (SA) modified tin dioxide-functionalized reduced graphene oxide (rGO-SnO2) /gold nanoparticles (AuNPs) served as a sensor platform for enhancing conductivity and immobilizing more Pb2+-specific DNAzyme. In the presence of Pb2+, the Pb2+-dependent DNAzyme specifically reacted with Pb2+, cleaving the substrate strand (SS) into two free fragment and releasing the biotin-modified enzyme strand (Bio-ES) on the electrode. Connecting MoS2–AuPt nanocomposites labeled with G-rich DNA (G-DNA) strand and exposure of Bio-ES through the Helper DNA, as well as adding hemin to form a hemin/G-quadruplex, the biosensor achieved signal amplification. Chronoamperometry was used to record the current signal, which was primarily derived from the cocatalysis reduction of H2O2 by MoS2–AuPt nanocomposites and the hemin/G-quadruplex. Under optimal conditions, the designed biosensor exhibited sensitive detection of Pb2+ from 0.1 pg mL−1 to 1000 ng mL−1, with a lower detection limit of 38 fg mL−1 (based on 3σ). This proposed biosensor is ultrasensitive and specific, representing a potential application for the detection of Pb2+ in a water environment.