A method of detecting two different target molecules through a single electrode is carried out by (a) providing a conductive oxidation-reduction reaction detection electrode; (b) contacting a sample suspected of containing a first and second target molecule to the electrode under conditions in which the first and second target molecules are deposited on the electrode, wherein the first target molecule comprises a first label and the second target molecule comprises a second label; (c) contacting to the electrode a first transition metal complex that oxidizes the first preselected label in a first oxidation-reduction reaction and a second transition metal complex that oxidizes the first and second labels in a second oxidation-reduction reaction, with the first and second oxidation-reduction reactions producing different detectable signals; (d) detecting the presence of the first target molecule by detecting the first oxidation-reduction reaction; and(e) detecting the presence of the second target molecule by detecting the second oxidation-reduction reaction. Devices for carrying out the method are also described.