Detection of chemically induced DNA damage in layered films by catalytic square wave voltammetry using Ru(Bpy)(3)(2+)

A sensor constructed by alternate layer-by-layer adsorption of PDDA cations and double-stranded (ds)-DNA on oxidized pyrolytic graphite electrodes was evaluated for detection of chemical damage to ds-DNA from known damage age nt styrene oxide. Films made with PDDA ions of structure (PDDA/DNA)(2) were similar to6 nm thick and contained 0.23 mug of ds-DNA. Catalytic oxidation using 50 muM RU(bPY)(3)(2+) (bpy = 2,2'-bipyridine) and square wave voltam metry (SWV) provided more sensitive detection of DNA damage than direct SWV oxidation. The catalytic peaks increased linearly with time during incubat ions with styrene oxide, but only minor changes were detected during incuba tion with nonreactive toluene. For best sensitivity, the outer layer of the film must be ds-DNA, and analysis should be done at low salt concentration . Studies of DNA and polynucleotides in solutions and films suggested that oxidation of guanine and chemically damaged adenine in partly unraveled, da maged DNA were the most likely contributors to the catalytic peak.