The proper selection of an enzyme immobilization method is important for the design of practical biosensors. The method of enzyme immobilization directly affects the operational stability and storage lifetime of the sensor.

General strategy for incorporation of enzymes into polyurethane materials such as foams, gels and coatings. The isocyanate group can react with the terminal amine of the enzyme or with the amino group present on lysine residues.

Immobilization methods for the fabrication of amperometric biosensors often rely on the entrapment of enzyme in a gel layer, which may be further coated by an external protective film. Interestingly, in the case of polyurethane/hydrophobic polyurethane based biosensors, the enzyme may be directly dispersed in the external hydrophilic polyurethane film. The lifetime and use of such systems are often limited by the diffusion of enzyme through the external membrane. To overcome this main disadvantage, the enzyme has to be directly and covalently immobilized into the coating.

Incorporation into a polymer network through multi-point attachment is a rapid and effective general strategy for enhancing the stability of enzymes, while retaining activity. This strategy involves the production of a bioplastic in a single step, employing monomers capable of chemical reaction with specific functionalities on the enzyme surface. The covalent binding provides protein retention in the matrix so that the advantages of immobilization can be maximized.