LONG-TERM OPERATIONAL STABILITY OF A MIXED GLUCOSE OXIDASE-REDOX MEDIATOR-CARBON PASTE ELECTRODE

The amperometric response of a mixed-glucose oxidase-redox mediator-carbon paste electrode, permanently poised at the operating potential, has been investigated in phosphate buffer as a function of glucose concentration over a period of four weeks. Results of the cyclic voltammetric data of the amphiphilic ferrocene mediator and the high positive operating potential applied (+ 0.6 V vs S.C.E) contributed significantly to the interpretation of the observed phenomena. The evolution of the apparent Michaelis-Menten constant (exponential decline) and the slope of the response (cyclic fluctuation) over the entire electrode lifetime support the suggestion that mediator leaching and gradual surface erosion mainly limit the analytical performance of the biosensor.