Reduction and oxidation of peptide nucleic acid and DNA at mercury and carbon electrodes

Peptide nucleic acid (PNA) is a DNA mimic that binds strongly and specifically to complementary DNA or RNA oligomers, but in contrast to DNA its backbone does not carry any electric charge. We used voltammetry in cyclic and square-wave modes to study reduction and oxidation signals of single stranded (ss)PNA and DNA decamers and pentadecamers with the same base sequences at mercury and carbon electrodes. The signals produced by the ssDNA and ssPNA oligomers at the hanging mercury drop electrode (HMDE), i.e. the cathodic peak CA (due to reduction of cytosine and adenine) and the anodic peak G (due to oxidation of the guanine reduction product) corresponded roughly to those observed earlier with ssDNAs. ssPNA peak potentials were more negative compared to DNA. Differences in the signals of ssPNA and ssDNA were explained primarily by different adsorption properties of these compounds. At an accumulation time of 5 min the detection limit of ssPNA was below 5 ng ml(-1) Constant current derivative chronopotentiometric stripping analysis (CPSA) at a pyrolytic graphite electrode produced two well-separated oxidation peaks of guanine and adenine residues in ssDNA and ssPNA in contrast to the poorly developed signals obtained by linear sweep (LS) and square wave (SW) voltammetries. The voltammetric signals were improved greatly as a result of application of a suitable baseline correction method. Using the polynomic method for LSV and moving average baseline correction for SWV, the ssDNA detection limits were comparable to those of CPSA at carbon electrodes as well to those obtained with peak G measurements at the HMDE. (C) 1999 Elsevier Science S.A. All rights reserved.