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Novel electrochemical DNA-based biosensors with outer-sphere Nafion and chitosan protective membranes were prepared for the evaluation of antioxidant properties of beverages (beer, coffee, and black tea) against prooxidant hydroxyl radicals. A carbon working electrode of a screen-printed three-electrode assembly was modified using a layer-by-layer deposition technique with low molecular weight double-stranded DNA and a Nafion or chitosan film. The membrane-covered DNA biosensors were initially tested with respect to their voltammetric and impedimetric response after the incubation of the beverage and the medium exchange for the solution of the redox indicator [Fe(CN)6]3−/4−. While the Nafion-protected biosensor proved to be suitable for beer and black tea extracts, the chitosan-protected biosensor was successfully used in a coffee extract. Afterwards, the applicability was successfully verified for these biosensors for the detection of a deep degradation of the surface-attached DNA at the incubation in the cleavage agent (hydroxyl radicals generated via Fenton reaction) and for the evaluation of antioxidant properties of coffee and black tea extracts against prooxidant hydroxyl radicals. The investigation of the novel biosensors with a protective membrane represents a significant contribution to the field of electrochemical DNA biosensors utilization.

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A DNA-based biosensor is presented that can be applied to the detection of DNA damage caused by UV-C radiation (254 nm) in the presence of CdTe quantum dots (QDs). The sensor is composed of a glassy carbon electrode whose surface was modified with a layer of dsDNA and another layer of CdTe QDs. The response of this sensor is based on (a) the intrinsic anodic signal of the guanine moiety in the DNA that is measured by square-wave voltammetry, and (b) the cyclic voltammetric response of the redox indicator system hexacyanoferrate(III/II). Depending on the size of the QDs, they exert a significant effect on the rate of the degradation of dsDNA by UV-C light, and even by visible light. Timedependent structural changes of DNA include opening of the double helix (as indicated by an increase in the redox response of the guanine moiety due to easy electron exchange with the electrode when compared to the original helix state and by an increase in the voltammetric peak current of the hexacyanoferrate(III/II) anion after degradation of the negatively charged DNA backbone on the electrode). The effects of QDs were verified for salmon sperm DNA and calf thymus DNA, and further corroborated by experiments in which DNA solutions were irradiated in the presence of QDs.