'Wiring' of lactate oxidase within a low-redox potential electron-conducting hydrogel

Lactate electrodes based on electron-conducting hydrogels made by cross-linking lactate oxidase and the redox polymer formed upon complexing polyvinyl imidazole with [Os(dmo-bpy)2Cl]+/2+ (dmo-bpy = 4,4'-dimethoxy-2,2'-bipyridine) on vitreous carbon electrode surfaces were investigated. The redox potential of the hydrogels was -69 mV, versus the standard calomel electrode (SCE), and their lactate electro-oxidation current reached a plateau at +50 mV (SCE). Urate and acetaminophen were not electro-oxidized at this potential at rates that would interfere with the lactate assays, but ascorbate was catalytically oxidized by the gel. At 6 mM lactate concentration, switching of the atmosphere from argon to O2, reduced the current by 40 percent, showing that the rate of electron transfer from the reduced enzyme to the gel was slow.