A triple-amplification differential pulse voltammetry for sensitive detection of DNA based on exonuclease III, strand displacement reaction and terminal deoxynucleotidyl transferase.

In this research, a sensitive and specific electrochemical biosensor for DNA detection was constructed. The highly sensitivity of this biosensor is due to the exploitation of exonuclease III-assisted double recycling and toehold-mediated strand displacement recycling to achieve the target triple recycling amplification, thus generating a large amount of Y-shaped DNA structures. Combination with a terminal deoxynucleotidyl transferase (TDT)-mediated cascaded signal amplification strategy can catalyze the repetitive incorporation of biotin-dUTP to the 3'-OH of the Y-shaped DNA. Via biotin-streptavidin interaction, multiple streptavidin-alkaline phosphatases were conjugated to the surface of an Au electrode and generated a sharply increasing electrochemical signal in a 1-naphthyl phosphate (1-NP) solution. In this method, an impressive detection limit of 0.05 fM was obtained, presenting outstanding selectivity with a dynamic response scope between 0.1 fM and 1 nΜ. Thus, the designed biosensor opens an avenue for DNA detection in clinical molecular diagnostics, pathogen detection, gene therapy, food safety and environmental monitoring.

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

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.