Electrochemical biosensor for amplified detection of Pb 2+ based on perfect match of reduced graphene oxide–gold nanoparticles and single-stranded DNAzyme

In this study, a sensitive amplification strategy for Pb2+ detection using reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) was proposed. Thiol-modified DNAzyme is specific for Pb2+ self-assembly on RGO-AuNPs-modified electrode surface. Ferrocene labeled single-stranded DNAzyme (Fc-ssDNAzyme) self-hybridizes to form a DNA hairpin structure. The amount of Fc adsorbed on the electrode surface changes after the appearance of Pb2+, leading to a change of electrical signal. This change can be sensitively identified by differential pulse voltammetry (DPV) assisted by ferricyanide ([Fe(CN)6]3−/4−) in the electrolyte. The high conductivity and specific surface area of RGO and the strong chemical bond adsorption effect between DNAzyme and AuNPs are responsible for the amplified detection of Pb2+, which realize a detection range of 0.05–400,000.0 nM and a minimum detection limit of 0.015 nM. Moreover, the selectivity test results indicated that the biosensor had specificity for Pb2+, even if there was interference from other high-concentration metal ions. This simple biosensor also exhibited good responsiveness in actual sample detection, which provides a good application prospect for field detection of Pb2+ in water.