Novel approaches for the use of mediators in enzyme electrodes

This work describes the preparation of glucose electrodes consisting of an enzyme (glucose oxidase) and a mediator embedded in a colloidal graphite emulsion matrix. These components are homogeneously mixed in an organic medium that evaporates rapidly while the enzyme activity remains intact. The appropriate conditions for preparation and measurement, as well as electrochemical characterization of these electrodes, are discussed. The problem of mediator leaching in electrodes using vinyl ferrocene was overcome by the use of a special membrane that prevented leaching of positive ferricinium ions by electrostatic repulsion under the appropriate measurement conditions, including minimal exposure of the electrode to anodic potentials, thus increasing the long-term stability. The resulting electrodes are easily prepared, have fast and high response independent of oxygen tension and can be stored in dry form. The linear range can be extended by the introduction of a dialysis membrane and can thus be adjusted to the measurement of glucose concentration in the range of medical interest.