Electrochemical responses of thiolated oligodeoxynucleotides in cobalt-containing solutions

We show for the first time that thiol end-labeled oligodeoxynucleotides (ODN) produce specific voltammetric signals at mercury and solid amalgam electrodes in cobalt-containing solutions (usually used in polarographic and voltammetric analysis of peptides and proteins). Most of the measurements were performed by adsorptive transfer stripping (ex situ) method. 21-mer ODN HS-(CTT)(7) was attached to the hanging mercury drop electrode (HMDE) and the DNA-modified electrode was immersed in the cobalt-containing empty background electrolyte. This ODN produced several differential pulse voltammetric signals which are not observed in absence of cobalt. The most negative signal (peak 3) of submicromolar HS-(CTT)(7) attained much larger heights than the catalytic (Brdicka) peaks of about 10-fold more concentrated cysteine-containing peptide. The peak 3 and a less negative peak 2 of the HS-ODN increased with increasing buffer concentration suggesting that, similarly to cysteine-containing peptides and proteins, for both SH-ODN peaks catalytic hydrogen evolution was responsible. Since peak 3 appeared at less negative potentials than the peptide Brdicka peaks it was possible to measure the ODN and peptide signals separately. This new possibility of measuring signals of thiolated DNA in the media, which proved suitable for protein analysis, can be utilized in the development of sensors for DNA-protein interactions, important in biomedicine and proteomics.