Modification-free electrochemical approach for sensitive monitoring of purine DNA bases: Simultaneous determination of guanine and adenine in biological samples using boron-doped diamond electrode

A simple and modification-free electrochemical sensor for sensitive determination of purine DNA bases based on the use of bare and electrochemically un-pretreated boron-doped diamond electrodes is proposed. Cyclic voltammetry showed that guanine and adenine provided well defined irreversible oxidation peaks at +1.15 and +1.35 V vs. Ag/AgCl/3 M KCl, respectively, in Britton–Robinson buffer solution at pH 6 with sufficient potential separation. Both analytes provided a linear relation between peak current and concentration in the range from 0.3 to 19 μM when both were present in the solution. For individual analytes in the absence of the other, the corresponding ranges for guanine and adenine were from 0.21 to 23 μM and from 0.12 to 25 μM, respectively. The limits of detection for guanine and adenine were 158 and 67 nM, respectively, for simultaneous determinations in differential pulse mode, and 37 and 19 nM, respectively, for individual quantifications. The proposed method was successfully applied for the assessment of guanine and adenine content in spiked human urine samples with satisfactory results. The analysis of native, thermally and acid denatured DNA samples from fish sperm and acid denatured DNA samples from human placenta yielded two oxidation peaks corresponding to guanine and adenine residues with (G + C)/(A + T) values close to those reported in literature. In this way, boron-doped diamond represents a modification-free electrochemical alternative to widely used modified electrodes for sensitive monitoring of purine DNA bases.