The “wired” technique is most commonly used today for enzyme immobilization and can be employed with Nafion® polymers, as shown in Figure 12.3. However, this approach decreases the activity of the enzyme due to the change in the three­dimensional configuration of the enzyme that results from covalent bonding between the enzyme and the polymer. Another problem associated with this technique is that the enzyme is still subjected to the chemical environment of the

FIGURE 12.3 Enzyme immobilization by “wiring” technique.

matrix and not protected from its surroundings. Therefore, the enzyme can be easily denatured, and this limits the lifetime of the enzymatic catalytic activity.

Sandwich Technique

A second type of enzyme immobilization employing Nafion® is the sandwich technique in which the enzyme is trapped in between the polymer and the electrode surface, as shown in Figure 12.4. This is accomplished by simply casting the enzyme solution onto an electrode surface before casting the Nafion® suspen­sion. Sandwich techniques are powerful and successful for enzyme immobiliza­tion; however, the enzyme’s optimal activity is not retained due to the physical distress applied by the polymer. In addition to this, the diffusion of analyte through the polymer is slowed limiting its applications.