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Halogenated phenols are widely used as biocides and are considered to be possibly carcinogenic to humans. In this report, a previously developed photoelectrochemical DNA sensor was employed to investigate DNA damage induced by tetra-halogenated quinones, the in vivo metabolites of halogenated phenols. The sensor surface was composed of a double-stranded DNA film assembled on a SnO2 semiconductor electrode. A DNA intercalator, Ru(bpy)2(dppz)2+, was allowed to bind to the DNA film and produce photocurrent upon light irradiation. After the DNA film was exposed to 300 μM tetrafluoro-1,4-benzoquinone (TFBQ), the photocurrent dropped by 20%. In a mixture of 300 μM TFBQ and 2 mM H2O2, the signal dropped by 40%. The signal reduction indicates less binding of Ru(bpy)2(dppz)2+ due to structural damage of ds-DNA in the film. Similar results were obtained with tetra-1,4-chlorobenzoquinone (TCBQ), although the signal was not reduced as much as TFBQ. Fluorescence measurement showed that TFBQ/H2O2 generated more hydroxyl radicals than TCBQ/H2O2. Gel electrophoresis proved that the two benzoquinones produced DNA strand breaks together with H2O2, but not by themselves. Using the photoelectrochemical sensor, it was also found that TCBQ covalently bound with DNA did not produce additional oxidative damage in the presence of H2O2. The combined photoelectrochemistry, gel electrophoresis, and fluorescence data revealed distinctive differences between TFBQ and TCBQ in terms of DNA adduct formation and hydroxyl radical generation. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

DNA films immobilized on an indium tin oxide (ITO) electrode surface were detected and determined employing a high-affinity intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine), as a redox indicator, and oxalate as a sacrificial electron donor in solution to chemically amplify the voltammetric signal of the indicator. Nucleic acids were immobilized on ITO by layer-by-layer electrostatic adsorption, using avidin as the first layer and nucleic acid as the second layer. In quartz crystal microbalance (QCM) measurements on an avidin-coated gold surface, the amount of adsorption from a 200 µg mL−1 nucleic acid solution was found to be 3.2 ng mm−2 for both double-stranded (ds-) and single-stranded (ss-) calf-thymus DNA as well as polycytidylic acid (Poly-C). After binding with Ru(bpy)2(dppz)2+ (Ru-dppz), voltammetry of the ds-DNA film on ITO was carried out in an indicator-free phosphate buffer. An anodic peak at about 1.15 V was observed, and it was assigned to Ru-dppz oxidation. When measured in an oxalate buffer, however, a catalytic current was observed due to the oxidation of oxalate by electrochemically generated Ru(bpy)2(dppz)3+, resulting in a 120-fold increase in the signal. Since oxalate itself produces a very low oxidation current on ITO, catalytic voltammetry produces about a 14-fold improvement in the signal-to-blank ratio over the non-amplified determination. As a result, ds-DNA adsorbed from 20 ng mL−1 solution could be detected, which was estimated by QCM to be 160 pg mm−2 on the surface. The catalytic current of ds-DNA was substantially higher than that of ss-DNA and poly-C, indicative of selective binding of the redox indicator to ds-DNA. The results serve as a basis for the catalytic voltammetric detection of DNA hybridization in future work. [ABSTRACT FROM AUTHOR]