Examination of Electron Transfer Through DNA Using Electrogene Rated Chemiluminescence

Three aminoalkanethiols that have large electron-transfer rate constants, SH−(CH2)n−NH2 (n = 6, 8, and 11), were individually self-assembled on Au electrodes, followed by covalent attachment of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) moieties onto the end of the thiols. Two separate electrogenerated chemiluminescence (ECL) waves were observed upon anodic potential scanning from 0 to 1.40 V vs Ag/AgCl (3 M KCl) over the electrode placed in 0.10 M tri-n-propylamine (TPrA)/0.10 M phosphate buffer (pH 7.4) solution. The first ECL wave, located at ∼0.88 V vs Ag/AgCl, was associated with the direct oxidation of TPrA at the electrode, and the second ECL wave, located at ∼1.12, 1.22, and 1.35 V vs Ag/AgCl for n = 6, 8, and 11, respectively, was directly related to the oxidation of the tethered Ru(bpy)32+ species. The electron transfer behavior through DNA was examined at Au electrodes, which were covalently immobilized with 15-mer and 20-mer single-stranded (ss) DNA, respectively, and then hybridized with the relevant complementary ssDNA tagged with Ru(bpy)32+ ECL labels. Under the same experimental conditions described above for Au/aminoalkanethiol-Ru(bpy)32+ studies, both double-stranded (ds) DNA displayed similar ECL responses, with the first ECL peak at ∼0.88 V and the second one at ∼1.22 V vs Ag/AgCl. No peak potential shift for the second ECL wave and no impact of the dsDNA on the entire electron transfer processes were observed, suggesting that complementary dsDNA helical structures can transfer electrons at a very large rate constant and that dsDNA studied were very conductive. In contrast, an electrode attached with 15-mer ssDNA-Ru(bpy)32+ did not show the second ECL wave, implying that ssDNA was not electronically conductive