A potentiometric sensing platform that enables real-time DNA hybridization detection is described. A model target DNA, t37s: 5'-AAA AAA AAA AAA-(TC)(2)-Ts-5-(TC)(2)-GGA GCT GGT GGC-3', which consist of a dodecamer polydeoxyadenylic acid and the human K-ras oncogene, and a five-successive deoxythymidine phosphorothioate (Ts) was designed. With the gold-phosphorothioate binding, the DNA could bind the complementarily sequences to concentrate them at the gold electrode surfaces. Accordingly, a dodecamer polydeoxythymidylic acid having ferroin-moiety (T12FeP) and a ferrocene-modified complementary of K-ras (KrasFc) were synthesized. Electrochemical quartz-crystal-microbalance (QCM) using Ausputtered quartz chips that served as the indicator electrode collected the electrode responses. When the electrode surface was treated with the T12FeP-hybridized t37s, which were subsequently oxidized to the corresponding Fe(III) form, the emf developed in a buffer solution responded to KrasFc; with the electrode-attached t37s the redox-active DNAs could group into a pair to establish specific redoxtitration equilibrium. A QCM confirmed the on-electrode titrimetry feasible by determining the initial concentration and the amount of hybridization along with the emf measurements. Although the present method is necessary for two-kinds of redox conjugation of the target DNA, it should be important as a novel framework of electrochemical gene sensing. Preliminary examples of real-time measurement were also demonstrated with the results of kinetics analysis data. (C) 2014 Elsevier B.V. All rights reserved.