Photoelectrochemical immunosensing platform for M. SssI methyltransferase activity analysis and inhibitor screening based on g-C3N4 and CdS quantum dots

DNA methylation is one of the important epigenetics events, and it is responsible for transcription, genomic imprinting and cellular differentiation. Aberrant DNA methylation is always contacted with various diseases. Herein, a simple and low-cost photoelectrochemical (PEC) biosensing method is proposed for detection of DNA methylation, assay of DNA methyltransferase (MTase) activity and screening of MTase inhibitor, which is based on M. SssI MTase-HpaII endonuclease system. The graphite-like C3N4 (g-C3N4) and CdS quantum dots (CdS QDs) are used as photoactive materials. After the double-stranded DNA (dsDNA) was treated with M. SssI MTase in the presence of S-adenosylmethionine, the methylated dsDNA cannot be digested by HpaII endonuclease and dithiol group at the terminal of dsDNA can be retained. As a result, CdS QDs could be coupled successfully with methylated dsDNA between the reaction of CdS QDs with dithiol of dsDNA, achieving the amplification of PEC response. Thus, the photocurrent of PEC biosensor is consistent with the M. SssI activity. The increased photocurrent was in proportion to M. SssI activity in the linear range from 1 to 80 U/mL with a detection limit of 0.316 U/mL. Furthermore, the effects of atrazine and azamethipos on M. SssI MTase activity were investigated, which might provide useful information on carcinogenic mechanism of pesticide. The PEC biosensor has potential to screen of DNA MTase inhibitor, providing valuable information for anti-cancer drug research and also for cancer therapy.