DNA-based biosensor for comparative study of catalytic effect of transition metals on autoxidation of sulfite

The transition metal-catalyzed oxidation of sulfur(IV) oxides has been known for more than 100 years. However, to the best of the authors' knowledge, no electrochemical quantitative study has yet been carried out to determine its nature. In view of the transition metal catalyzed oxidation of sulfur(IV) oxides, a series of radicals are involved in the overall reaction process whereby the sulfite, in the presence of transition metals, may cause damages to DNA through the generation of these highly reactive species. In the present work, {MWCNTs-PDDA/DNA}(2) layer-by-layer (LBL) films were prepared to detect DNA damage induced by radicals generated from sulfite autoxidation using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The change in the peak potential separation (ΔE(p)) and charge transfer resistance (R(p)) after incubation of the DNA biosensor in the damaging solution for a certain time was used as indicators of DNA damage. It was found that sulfite in the presence of Co(II), Cu(II), Cr(VI), Fe(III), and Mn(II) caused damage to DNA while neither sulfite alone nor metal ions alone did have the same effect. The results suggest that sulfite is rapidly autoxidized in the presence of Co(II), Cu(II), Cr(VI), Fe(III), and Mn(II), producing radicals that cause the DNA damage. These radicals can be ranked in a descending order of their ability to induce DNA damage with sulfite as follows: Fe(III) > Co(II) > Cu(II) > Cr(VI) > Mn(II). The DNA damage induced by sulfite plus Co(II), Cr(VI), and Fe(III) was inhibited by primary alcohols, but they were not when superoxide dismutase (SOD) and tert-butyl alcohol were used. Comparison of methods used to determine the minimum concentration of a transition metal for sulfite induced DNA damage revealed that electrochemical impedance spectroscopy and cyclic voltammetry outperformed the quantitative comparison of different reagents.