▎ 摘　　要

DNA methyltransferase enzyme has a crucial role in many biological processes. Abnormal expression level of this enzyme has been regarded as a predictive cancer biomarker. Herein a novel method based on DNA modified GQDs was developed for fluorescence based assay and anisotropic investigation of M.Sssi activity. An amine modified ds-DNA was designed including a recognition site for both methyltransferase M.Sssl and endonuclease HpalI. By conjugation of ds-DNA to GQDs, fluorescence was decreased to 45%. When M.Sssl was introduced, ds-DNA was methylated at palindromic sequence 5'...CCGG...3' and become resistant to cleavage by HpalI and no change was observed in fluorescence intensity. Contrarily without sufficient M.Sssl enzyme, Hpall cleaved DNA strands and induced enhancement of fluorescence. The proposed method exhibited a low detection limit of 0.7 U/ml. Additional fluorescence anisotropy method was performed to confirm the DNA modification and release of DNA strands from the surface of GQDs in the presence of M.Sssl and HpaIl respectively. The application of the assay in the serum sample was successfully investigated. This simple method can be a useful tool to apply in diagnosis and biomedical research. (C) 2016 Elsevier B.V. All rights reserved.