Improving the selectivity and stability of amperometric 'wired' enzyme electrodes

Glucose and lactate electrodes based on hydrogels made by crosslinking glucose oxidase and the redox polymer formed upon complexing either polyvinyl pyridine (PVP) or polyvinyl imidazole (PVI) with (Os(dmo-bpy){dollar}sb2{dollar}Cl) {dollar}sp{lcub}+/2+{rcub}{dollar} (dmo-bpy = 4,4{dollar}spprime{dollar}-dimethoxy-2,2{dollar}spprime{dollar}-bipyridine) on vitreous carbon electrode surfaces were investigated. The redox potentials of the hydrogels made with the PVI-based and the PVP-based redox polymers were {dollar}-{dollar}65mV and +35mV (SCE) and their glucose electrooxidation currents reached plateaus at +50 mV and +150mV (SCE), respectively. At these potentials, urate and acetaminophen were not electrooxidized at rates that would interfere with the sensor assays. The PVP-based redox polymer exhibited better performance in the presence of ascorbate and oxygen.; Glucose and lactate sensors maintaining stable output under continuous operation at 37{dollar}spcirc{dollar}C for 12 and 8 days, respectively, were built. The vitreous carbon base of the sensor was coated with four polymer layers. The first was made by cross-linking thermostable soybean peroxidase and an osmium based redox polymer; the second was an insulating cellulose acetate layer; the third was an immobilized oxidase layer; and the fourth was another cellulose acetate layer. The glucose sensor had a current output that was independent of potential between {dollar}-{dollar}0.2 V and +0.3 V (vs. SCE), independent of the O{dollar}sb2{dollar} partial pressure above 15 torr and insensitive to both motion and interferants. The operational stability was oxidase loading dependent.; Lactate oxidase and glucose oxidase were immobilized within silica gels formed by the acid catalyzed condensation reaction of tetramethylorthosilicate (TMOS). The resultant gels were ground into powders, and the thermostability of their enzymatic activity of the powder gels was tested in water between 50{dollar}spcirc{dollar}C and 92{dollar}spcirc{dollar}C. The lactate oxidase immobilized in silica gel exhibited stability similar to that of lactate oxidase in solution. However, electrostatic complexation of lactate oxidase with poly(1-vinyl imidazole) (PVI) before its immobilization in the silica gel provided greatly improved stability at elevated temperatures. Glucose oxidase was also immobilized in silica gel and likewise displayed improved stability characteristics.