DNA–gold nanoparticles network based electrochemical biosensors for DNA MTase activity

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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 30U/mL, achieving a low detection limit of 0.02U/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.