Simultaneous direct electrochemiluminescence and catalytic voltammetry detection of DNA in ultrathin films

Direct electrochemiluminescence (ECL) involving DNA was demonstrated in 10 nm films of cationic polymer [Ru(bpy)(2)(PVP)(10)](2+) assembled layer-by-layer with DNA. A square wave voltammetric waveform oxidized the Ru-II sites in the metallopolymer to Ru-III, and ECL was measured simultaneously with catalytic voltammetric peaks in a simple apparatus. Significant ECL generation occurred only when guanine bases were present on oligonucleotides in the films. This result along with knowledge of proposed ECL pathways suggests that guanine radicals initially formed by catalytic oxidation of guanines by Ru-III react with the metallopolymer to produce electronically exited Ru-II* sites in the film. ECL and catalytic SWV peaks were sensitive to oligonucleotide hybridization and chemical DNA damage. Simultaneous linear growth of ECL and SWV peaks occurred after incubation with known DNA damage agent styrene oxide over 20 min. The estimated detection limit was 1 damaged DNA base in 1000. Control incubations of metallopolymer/dsDNA films in buffer containing unreactive toluene resulted in no significant changes of the ECL or SWV peaks.