Mass transport and reaction kinetic parameters determined electrochemically for immobilized glucose oxidase

Mass-transfer resistances often have pronounced effects on the overall reaction rates of enzymes immobilized at interfaces or in polymeric matrices. In the present work glucose oxidase was immobilized on the surface of a platinum disk electrode by one of three attachment techniques: silane-glutaraldehyde, allylamine-glutaraldehyde, and albumin-glutaraldehyde. In one group of studies the electrodes were rotated, and methods were employed to determine the diffusion and shielding coefficients for transport of a model electroactive compound, i.e., potassium ferrocyanide, through the enzyme matrix. A model electrochemically active compound was used because glucose exhibits a very slow rate of electron transfer at a platinum surface. The diffusion coefficient for ferrocyanide was reduced 7% by the silane-enzyme and 25% by the allylamine-enzyme matrices. In a second group of studies the electrodes were held stationary. Marked internal diffusional resistance was noted for the albumin-glutaraldehyde-enzyme matrix. The calculated flux of ferrocyanide was decreased by a factor of 2000-8500 for transport through albumin-enzyme matrices 0.21-0.063 cm thick, as compared to transport through free solution. In a third group of studies the rotating enzyme-matrix electrode was utilized in determining apparent values of the Michaelis constant for glucose. The velocity of the reaction was determined by amperometric measurement of the concentration of hydrogen peroxide reaching the ring electrode. The results, determined from Eadie-Hofstee type plots of reaction current and substrate concentration, gave values between 12 and 36 mM for the three methods of immobilization.(ABSTRACT TRUNCATED AT 250 WORDS)