DNA-gold nanoparticles network based electrochemical biosensors for DNA MTase activity.

In this work, a highly sensitive electrochemical DNA methyltransferase (MTase) activity assay was fabricated with DNA-gold nanoparticles (Au NPs) network as signal amplification unit and an easy assembly method by the linkage of benzenedithiol bridge. By two complementary AuNPs modified single-stranded DNA, DNA-gold nanoparticles network was self-assembled. With the linkage of benzenedithiol bridge, the DNA network structure was immobilized on the surface of gold electrode through the covalent Au-S bond. In the presence of Dam MTase, the special sites of DNA-AuNPs network were methylated and could not be digested by restriction endonuclease Mbo I. Thus the loaded electrochemical indicator Methylene blue (MB) was MB molecules still remained on the DNA-Au NPs network. The electrochemical response depended on the methylated degree, which could be used to detect MTase activity. By the differential pulse voltammetry (DPV), it was demonstrated that a linear relationship between the DPV response and logarithm of Dam concentration ranged from 0.075 to 30 U/mL, achieving a low detection limit of 0.02 U/mL. The use of benzenedithiol avoided the direct incubation of the solid electrode with the capture DNA probe under complex and harsh conditions. Therefore the immobilization of DNA-AuNPs network was easy to be carried out, which is favorable for the specially high stability and reproducibility of the electrochemical biosensor.