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Antioxidant redox sensors based on DNA modified carbon screen-printed electrodes were developed. The carbon ink was doped with TiO2 nanoparticles, onto which double-strand DNA was adsorbed. A redox mediator, namely, tris-2,2'-bipyridine ruthenium(II) [Ru(bpy)3(2+)] was electrooxidized on the electrode surface to subsequently oxidize both the adsorbed ds-DNA and the antioxidants in solution. The resulting oxidation damage of the adsorbed ds-DNA was then detected by square wave voltammetry in a second solution containing only Ru(bpy)3Cl2 at a low concentration (microM). A kinetic model was developed to study the protecting role of antioxidants in aqueous solutions. The electrochemical sensor has been applied to evaluate the redox antioxidant capacity of different molecules.

TiO2/ITO modified electrodes were developed to quantitatively photooxidize adsorbed ds-DNA and to study the effect of antioxidants as ds-DNA protecting agents. TiO2 films are used for efficient ds-DNA immobilization, for ds-DNA oxidation through photogenerated hydroxyl radicals, and as electrodes for amperometric sensing. The films, prepared by a sol-gel process, are deposited on ITO glass electrodes. Damages occurring after ds-DNA oxidation by ROS are detected by adding MB as an intercalant probe and by monitoring the electrochemical reduction current of the intercalated redox probe. The MB electrochemical signal is found to be sensitive enough to monitor ds-DNA structure changes, and the electrochemical sensor has been applied to the evaluation of the antioxidant properties of glutathione and gallic acid.