Square wave voltammetric detection of chemical DNA damage with catalytic poly(4-vinylpyridine)-Ru(bpy)2(2+) films

Reversible, catalytic films of poly(4-vinylpyridine)-Ru(bpy)2(2+) [PVP-Ru(bpy)2(2+), bpy = 2,2'-bipyridine] on pyrolytic graphite (PG) electrodes were evaluated for the detection of damage to double-stranded (ds) DNA by using square wave voltammetry (SWV). Damage of both calf thymus and salmon testes ds-DNA in solution was induced by incubation of DNA at 37 degrees C with styrene oxide, the liver metabolite of styrene, and a suspected carcinogen. Both types of ds-DNA incubated in solution with saturated styrene oxide gave a linear increase in catalytic peak current up to 30 min, and an estimate of two damaged DNA bases in one thousand could be detected. The increase in catalytic current is attributed to better access of the catalyst redox sites to oxidizable bases in the damaged, partly unwound DNA. A self-contained "toxicity sensor" was also evaluated, which consisted of films of [PVP-Ru(bpy)2(2+)] on PG electrodes coated with films of ds-DNA and polydiallyldimethylammonium polycations assembled layer-by-layer. These films also gave an increase in catalytic peak current upon incubation in saturated styrene oxide, and an estimate of 1 damaged base in 1000 could be detected. Control films or solutions of ds-DNA treated in buffer or buffer containing unreactive toluene resulted in no significant changes in the catalytic peak current with incubation time.