Label-free detection of canonical DNA bases, uracil and 5-methylcytosine in DNA oligonucleotides using linear sweep voltammetry at a pyrolytic graphite electrode

An innovative approach to label-free voltammetric analysis of DNA at a pyrolytic graphite electrode (PGE) within a broad range of potentials (from −2.0 to +1.6V) in an acetate buffer (pH5) is presented. Using specifically designed DNA nonamers, we demonstrate not only anodic oxidation, but for the first time also cathodic reduction of nucleobases at the PGE. In addition, products of irreversible oxidation/reduction of the parent bases are shown to yield analytically useful, base-specific cathodic/anodic signals, making it possible to distinguish between the canonical bases (adenine, cytosine, guanine and thymine), uracil (U) and 5-methylcytosine (mC) in DNA. Furthermore, selective electrochemical “switching off” of the redox signals specific to certain nucleobases is presented as a way to resolve overlapping signals. Similarly, newly reported signals corresponding to electrochemically transformed bases can be “switched on” under specific conditions. This approach can be utilized for fast and facile simultaneous label-free analysis of bases in DNA, including mC and U, and to uncover overlapping signals. This significantly extends the possible applications of PGE in DNA research and (bio)sensor development. Keywords: 5-Methylcytosine, DNA, Electrochemistry, Electrochemical reduction, Electrochemical oxidation, Pyrolytic graphite