From Thick Films to Monolayer Recognition Layers in Amperometric Enzyme Electrodes

Theoretical models of the conventional thick-film enzyme electrode and monolayer electrodes are used to determine the important parameters in defining the response of both types of biosensors with regard to their reproducible fabrication. The response of the thick-film biosensors are very sensitive to the thickness of the enzyme layer and therefore highly precise methods of depositing the enzyme layer are required if reproducible biosensors are to be manufactured. Covalent attachment of an enzyme to a monolayer of alkanethiols self-assembled onto a gold electrode could potentially provide this more precise fabrication method. A model for monolayer enzyme electrodes gives an excellent fit to an experimental calibration plot for a monolayer of glucose oxidase attached to a self-assembled monolayer. The model showed the response was highly dependent on the amount of enzyme immobilized and therefore the reproducibility of monolayer enzyme electrodes will be limited by the reproducibility of the enzyme immobilization. The model predicts the response of the monolayer biosensor is limited by the turnover rate of the enzyme rather than the supply of substrate as is the case with thick-film biosensors.