Electrical detection of single methylcytosines in a DNA oligomer.

We report label-free electrical detections of chemically modified nucleobases in a DNA using a nucleotide-sized electrode gap. We found that methyl substitution contributes to increase the tunneling conductance of deoxycytidines, which was attributed to a shift of the highest occupied molecular orbital level closer to the electrode Fermi level by methylation. We also demonstrate statistical identifications of methylcytosines in an oligonucleotide by tunneling current. This result suggests a possible use of the transverse electron-transport method for a methylation level analysis.