Interactions of an anisomerous ruthenated porphyrin [Ru(MPyTPP)(bpy)(2)Cl](+) (where bpy = 2,2'-bipyridine, MPyTPP = 5-pyridyl-10,15,20-triphenyl porphyrin) with calf thymus DNA are studied using a tin-doped indium oxide (ITO) electrode. The Ru-III/II redox reaction for the complex exhibits a surface-controlled electron transfer process in buffer solutions. There exists an obvious interaction of the adsorbed [Ru(MPyTPP)(bpy)(2)Cl](+) on an ITO electrode with DNA in the buffer solutions. The formal potential for [Ru(MPyTPP) (bPY)(2)CI](2+/+) redox reaction is found to shift negatively in the presence of DNA compared with that in the absence of DNA. However, the current signals of [Ru(bPY)(3)](3+/2+) reaction exhibits a distinct catalytic enhancement to DNA, in contrast to the interactions of [Ru(MPyTPP)(bpy)(2)CI](+) with DNA. (c) 2006 Elsevier B.V. All rights reserved.