▎ 摘　　要

Silencing of tumor suppressor genes (E-cadherin) by promoter DNA methylation may lead to the development of invasive phenotypes in epithelial tissues. The authors describe an electrochemical nanobiosensor for early detection and screening of circulating methylated DNA as a biomarker for cancers. First, the antibody against5-methylcytosine was physically immobilized onto modifiedwith reduced graphene oxide andpolyvinylalcohol. In the next step, methylated target DNA in samples was hybridized with ssDNA probe conjugated to Fe3O4-citric acid nanocomposites and placed on the modified electrode. Then, the hexacyanoferrateredox systemwas added and electron transfer recorded. Cyclic voltammetry and electrochemical impedance spectroscopy showed that the modification process was well accomplished. Quantitative measurement of E-cadherin DNA promoter methylation was performed using differential pulse voltammetry. The electrochemical analysis achieved in the presence and absence of nonmethylated DNA mixed with samples indicated the high specificity and selectivity in methylation analysis using this system. With the linear range of concentration from 1x10(-4)ng.mL(-1) to 20ng.mL(-1) and the detection limit of 9x10(-5)ng.mL(-1), this method represents a promising approach for analysis of other biomarkers.