Abstract: A variety of diazacyanine mediators that are soluble in aqueous media and which do not inhibit enzymatic activity are provided for use on the surface of a working electrode of a electrochemical biosensor for electrochemical co-enzyme regeneration. The co-enzyme, dihydronicotinamide adenine dinucleotide (NADH) or dihydronicotinamide adenine dinucleotide phosphate (NADPH), is oxidized to NAD.sup.+ OR NADP.sup.+ which is reduced by an oxidoreductase such as a dehydrogenase acting on a substrate. By applying the mediator together with NADH or NADPH to the surface of the working electrode, the voltage necessary to achieve oxidation is substantially reduced. Biosensor electrodes such as graphite electrodes may be produced-by screen printing techniques.

Abstract: Disclosed is an improved electrode suitable for the electrochemical regeneration of the co-enzymes NADH and NADPH. The electrode has imparted on its surface a mediator function which is a 3-phenylimino-3H-phenothiazine or a 3-phenylimino-3H-phenoxazine. Also disclosed is a method of improving the performance of a biochemical fuel cell which operates with a dehydrogenase as a catalyst and a co-enzyme as the energy-transferring redox couple which involves using the improved electrode in the fuel cell.

Abstract: A method of making and an amperometric electrode are provided. An electrode carbon ink is applied to a polymer substrate to form a working electrode. The substrate carrying the working electrode is placed in a gas plasma cleaner, such as an oxygen or nitrogen plasma, to clean the working electrode. A high radio frequency signal excites the gas plasma for a short exposure time in a range between 10 seconds and 30 seconds. Then a reagent layer is deposited to the plasma treated working electrode.