Electrochemical detection of single-stranded DNA using polymer-modified electrodes

Glassy carbon electrodes modified by reductive electropolymerization of a thin film of poly[Ru(vbpy)(3)(2+)] or poly[Ru(vbpy)(3)(2+)/vba] (vbpy = 4-vinyl-4'-methyl-2,2'-bipyridine and vba = p-vinylbenzoic acid) were prepared. The Ru(III/II) couples for the polymer films were reversible in nonaqueous solution but were irreversible in aqueous media. The films modified with poly[Ru(vbpy)(3)(2+)] catalyzed the oxidation of aqueous guanosine 5'-monophosphate (GMP) and poly[G], producing a current enhancement in the Ru(III/II) couple for the polymer film. The catalysis was due both to electrostatic condensation of GMP and poly[G] to the Ru-modified surface and to more facile electron transfer to the Ru(III) centers in the polymer compared to the bare electrode. The presence of GMP in solution decreased the extent of decomposition of Ru(III). When single-stranded DNA containing multiple guanines was attached to the electrode modified with the poly[Ru(vbpy)(3)(2+)/vba] copolymer, enhancement of 8-13 mu A for the Ru(III/II) couple was observed with 8 pmol of attached DNA. This degree of enhancement corresponds to a current efficiency of 65% based on a one-electron oxidation of guanine.