A colorimetric assay of DNA methyltransferase activity based on the keypad lock of duplex DNA modified meso-SiO2@Fe3O4.

Abnormal level of DNA methyltransferase (MTase) - mediated DNA methylation is closely related with cancer and bacterial diseases. Herein, a novel strategy based on the keypad lock of duplex DNA modified meso-SiO2@Fe3O4 was developed for colorimetric assay of Dam MTase activity. When the Dam MTase was introduced, the duplex DNA can be methylated at a palindrome sequence of 5'-GATC-3' and cleaved by the methylation-sensitive restriction endonuclease Dpn I. Due to the instability of the newly formed DNA fragment, the hybrid will separated into a single-stranded DNA. Then the keypad lock will open, and the catalytic reaction of TMB and H2O2 can be initiated through the pores of meso-SiO2@Fe3O4, and a high color signal can be clearly observed by the naked eye. Contrarily, without Dam MTase, the catalytic reaction will not be initiated, and result no color signal. The proposed method exhibited a wide dynamic range with a low detection limit of 0.73 U/mL. Additionally, this way can be performed in human serum with satisfying recovery. And the inhibition of Dam MTase can also be well demonstrated by using paclitaxel as a model. Therefore, the designed way not only provides a platform for monitoring Dam MTase activity, but also useful for further application in disease diagnosis and drug discovery.