Use of polished and mercury film-modified silver solid amalgam electrodes in electrochemical analysis of DNA
Polished and mercury film-modified silver solid amalgam electrodes (p-AgSAE and MF-AgSAE, respectively) were used for the measurements of intrinsic redox (faradic) and tensammetric voltammetric signals of, single- (ss) and double-stranded, linear (lin) or supercoiled (sc) DNAs, synthetic polynucleotides and free adenine base. At the MF-AgSAE, all of these species yielded signals similar to those previously obtained on the hanging mercury drop electrode (HMDE) or on solid silver amalgam electrode modified with mercury meniscus (m-AgSAE). Good measurable anodic peak G (due to guanine residues) and tensammetric signals of ssDNA were obtained also with the p-AgSAE (albeit the latter appeared at significantly less negative potentials than respective signals measured at HMDE). In contrast, the cathodic DNA peak CA (due to reduction of cytosine and adenine residues) was not detected at the polished electrode. For the free adenine base, at least an order of magnitude lower sensitivity (compared to HMDE or MF-AgSAE) was achieved when its reduction signal was measured. Double-stranded DNAs (including sc and linDNA) yielded no measurable tensammetric signals at the p-AgSAE. Similarly as with the HMDE and m-AgSAE, measurements at the MF-AgSAE allowed differentiation between sc and linDNA and were successfully applied for the detection of DNA strand breaks induced by ionizing radiation. The p-AgSAE could be used for detection of the DNA strand breaks too, but selective denaturation of the damaged DNA (converting it into ssDNA detectable at the polished electrode) was necessary prior to the voltammetric analysis. Our results suggest that the different behavior of DNA at the p-AgSAE and at the MF-AgSAE (HMDE) is probably related to a considerably weaker adsorption of the DNA molecules on the polished solid amalgam surface, compared to the surface of mercury (or liquid silver amalgam).