An electrochemical biosensor for detecting DNA methylation based on AuNPs/rGO/g-C₃N₄ nanocomposite

DNA methylation as a ubiquitously regulation is closely associated with cell proliferation and differentiation. Growing data shows that aberrant methylation contributes to disease incidence, especially in tumorigenesis. The approach for identifying DNA methylation usually depends on treatment of sodium bisulfite, which is time-consuming and conversion-insufficient. Here, with a special biosensor, we establish an alternative approach for detecting DNA methylation. The biosensor is consisted of two parts, which are gold electrode and nanocomposite (AuNPs/rGO/g-C₃N₄). Nanocomposite was fabricated by three components, which are gold nanoparticles (AuNPs), reduced graphene oxide (rGO) and graphite carbon nitride (g-C₃N₄). For methylated DNA detection, the target DNA was captured by probe DNA immobilized on the gold electrode surface through thiolating process and subjected to hybrid with anti-methylated cytosine conjugated to nanocomposite. When the methylated cytosines in target DNA were recognized by anti-methylated cytosine, a change of electrochemical signals will be observed. With different size of target DNAs, the concentration and methylation level were tested. It is shown that in short size methylated DNA fragment, the linear range and LOD of concentration is 10^-7M-10^-15M and 0.74 fM respectively; in longer size methylated DNA, the linear range of methylation proportion and LOD of copy number is 3%-84% and 10³ respectively. Also, this approach has a high sensitivity and specificity as well as anti-disturbing ability.