Abstract
The tremendous demand for detecting methylated DNA has stimulated intensive studies on developing fast single-molecule techniques with excellent sensitivity, reliability, and selectivity. However, most of these methods cannot directly detect DNA methylation at single-molecule level, which need either special recognizing elements or chemical modification of DNA. Here, we report a tetramethylammonium-based nanopore (termed TMA-NP) sensor that can quickly and accurately detect locus-specific DNA methylation, without bisulfite conversion, chemical modification or enzyme amplification. In the TMA-NP sensor, TMA-Cl is utilized as a nanopore-filling electrolyte to record the ion current change in a single nanopore triggered by methylated DNA translocation through the pore. Because of its methyl-philic nature, TMA can insert into the methylcytosine-guanine (mC-G) bond and then effectively unfasten and reduce the mC-G strength by 2.24 times. Simultaneously, TMA can increase the stability of A-T to the same level as C-G. The abilities of TMA (removing the base pair composition dependence of DNA strands, yet highly sensing for methylated base sites) endow the TMA-NP sensor with high selectivity and high precision. Using nanopore to detect dsDNA stability, the methylated and unmethylated bases are easily distinguished. This simple single-molecule technique should be applicable to the rapid analysis in epigenetic research.