T4 DNA polymerase-assisted upgrade of a nicking/polymerization amplification strategy for ultrasensitive electrochemical detection of Watermelon mosaic virus.

An upgraded nicking/polymerization strategy for ultrasensitive electrochemical detection of Watermelon mosaic virus (WMV) is proposed on the basis of the exonuclease and polymerase activity of T4 DNA polymerase and Mg2+-dependent DNAzyme-assisted and hemin/G-quadruplex DNAzyme-assisted cascade amplification strategies. Briefly, the hybridized DNA of the target WMV sequence, HP1, and P1 was recognized and nicked by nicking endonuclease Nb.BbvCI, and two DNA segments (P1-25 and P1-6) were produced. P1-25 was digested in the 3'→5' direction, and digestion was halted at the 3'-terminal G locus with the exonuclease activity of T4 DNA polymerase. When dNTP solution mix was added to the mixture, an intact enzymatic sequence of Mg2+-dependent DNAzyme was synthesized by T4 DNA polymerase, which hybridized with its substrate sequence in the loop segment of HP2 immobilized on a gold electrode and initiated the cleavage round. The caged G-quadruplex sequence was released and formed hemin/G-quadruplex-based DNAzyme, resulting in sharply increased electrochemical signals. A correlation between the differential pulse voltammetry signal and the concentration of target WMV sequence was obtained in the range from 50 fM to 1 nM, with 50 fM detection limit. Because the nicking and polymerization reactions are irreversible and share the same buffer, the cascade amplification strategy is an ultrasensitive and high-efficiency strategy, indicating potential for viral detection. Graphical abstract An upgrade nicking/polymerization strategy for ultrasensitive electrochemical detection of Watermelon mosaic virus (WMV) was proposed based on DNAzyme-assistant cascade amplification strategies.