Sources of instability of 'wired' enzyme anodes in serum: urate and transition metal ions

The glucose electrooxidation currents of anodes with films of glucose oxida se and redox polymers electrically connecting ('wiring') its redox centers to electrodes decay much more rapidly in serum than in pH 7.2 saline phosph ate buffer. Rapid decay is observed also in buffer in the presence of urate and transition metal ions, which are constituents of normal serum. Urate i s electrooxidized to dimeric or trimeric products, which precipitate in the electrocatalytic film. Transition metal ions, like Zn2+ and Fe2+, coordina tively crosslink pyridine or imidazole functions of the redox polymers and also inhibit glucose oxidase. (C) 2001 Elsevier Science B.V. All rights res erved.