Detection and mechanistic investigation of halogenated benzoquinone induced DNA damage by photoelectrochemical DNA sensor

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 SnO(2) 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 mu M tetrafluoro-1,4-benzoquinone (TFBQ), the photocurrent dropped by 20%. In a mixture of 300 mu M TFBQ and 2 mM H(2)O(2), 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-chloro-benzoquinone (TCBQ), although the signal was not reduced as much as TFBQ. Fluorescence measurement showed that TFBQ/H(2)O(2) generated more hydroxyl radicals than TCBQ/H(2)O(2). Gel electrophoresis proved that the two benzoquinones produced DNA strand breaks together with H(2)O(2), 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 H(2)O(2). 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.