From thick films to monolayer recognition layers in amperometric enzyme electrodes

Theoretical models of the conventional thick-film enzyme electrode and mono layer 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 o f depositing the enzyme layer are required if reproducible biosensors are t o be manufactured. Covalent attachment of an enzyme to a monolayer of alkan ethiols self-assembled onto a gold electrode could potentially provide this more precise fabrication method. A model for monolayer enzyme electrodes g ives an excellent fit to an experimental calibration plot for a monolayer o f glucose oxidase attached to a self-assembled monolayer. The model showed the response was highly dependent on the amount of enzyme immobilized and t herefore the reproducibility of monolayer enzyme electrodes will be limited by the reproducibility of the enzyme immobilization. The model predicts th e response of the monolayer biosensor is limited by the turnover rate of th e enzyme rather than the supply of substrate as is the case with thick-him biosensors.