Ultratrace measurements of nucleic acids by baseline-corrected adsorptive stripping square-wave voltammetry

The direct and reliable electrochemical detection of DNA is of paramount importance to the development of modern DNA hybridization chips, for the detection of nucleic acids following their electrophoretic separations, or for the sensing of DNA damage and interactions. Such solid electrode voltammetric measurements of nucleic acids have been traditionally hampered by the large solvent decomposition background current that obscures the oxidation signals of the purine nucleobases. This paper reports on the use of adsorptive stripping square-wave voltammetry, in connection with the "moving average baseline correction" approach, for monitoring ultratrace levels of DNA and RNA. Compared to other baseline-fitted or background-subtraction protocols, the moving average baseline scheme is particularly effective in isolating the small purine nucleobase peaks, which appear as small shoulders on the steep background discharge contribution. The remarkably flat baseline thus obtained (up to extreme potentials) leads to a dramatic lowering of the detection limits to the femtomole level and to a performance that compares favorably with that of computerized chronopotentiometric measurements of nucleic acids. Combined with the speed of square-wave voltammetric measurements, such developments should expand the role of voltammetry in DNA diagnostics and nucleic acid research.