TRACE MEASUREMENTS OF PLASMID DNAS BY ADSORPTIVE STRIPPING POTENTIOMETRY AT CARBON-PASTE ELECTRODES

Supercoiled, linear and denatured forms of plasmid pUC 19 DNA can be a dsorbed at carbon paste (CPE) and pyrolytic graphite (PGE) electrodes and detected by constant current chronopotentiometric stripping analys is (PSA) at low bulk concentrations. The determination is based on the PSA peak at about 1.0 V (against Ag/AgCl) due to the oxidation of gua nine residues in the DNA. In agreement with earlier voltammetric data obtained with chromosomal DNAs at carbon electrodes, the denatured DNA produces a higher signal than linear and supercoiled DNAs. Compared w ith voltammetry, the sensitivity of PSA is higher by several orders of magnitude. PSA detection limits (obtained with a CPE) are about 100 n g ml(-1) for supercoiled and linear DNAs and 15 ng ml(-1) for denature d DNA. This great increase in sensitivity of the analysis at carbon el ectrodes offers new possibilities for electrochemical research, involv ing various forms of plasmid DNA.