Determining methylation state of a particular DNA sequence is an essential task in many epigenetic investigations. Here a facile method based on silver nanocluster (AgNCs) fluorescence enhancement is presented. Target sequences were selected from Sept9 promoter region that its hypermethylation is demonstrated as a reliable biomarker of colorectal cancer. Probe DNA was complementary to a 25 nucleotide of the target region and possessed twelve additional cytosines in the middle to grant the formation of AgNCs. After probe strands were hybridized with methylated and non-methylated targets separately, AgNCs were synthesized, and their fluorescence intensities were recorded. Fluorescence intensity enhanced when the target strands were methylated and quenched when they were non-methylated. The Linear range of fluorescence enhancement was from 1.0 × 10-7 M to 5.0 × 10-7 M with the detection limit of 7.6 × 10-8 M. Sensor specificity was checked with non-complementary strands with the maximum similarity of 40%. Further experiments explored various characteristics of methylated and non-methylated DNAs carrying AgNC and indicated that structure of methylated and non-methylated DNAs was affected differently by silver ions that could then influence AgNC fluorescence. This effect was strongly sequence-dependent, and either fluorescence enhancement or quenching was observed with two different sequences.
Keywords: DNA methylation; Fluorescent enhancement; Septin9; Silver nanoclusters; Turn-on.
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