PTFE offers support

Immobilizing the troops. By immobilizing the enzyme alliinase to a poly(tetrafluoroethylene) matrix, researchers created a bioreactor for the production of allicin, pyruvic acid, and ammonia.

Now, a German team believes that it has found a way to functionalize PTFE for use in membranes and powders that have potential as multifunctional supports (Biotechnol. Bioeng. 2001, 72, 530–540). The team attached biomolecules to the usually “nonstick” surface by using elemental sodium and then ozone or peroxide oxidation to open up putative covalent attachment points.

By optimizing the process, the team achieved the highest enzyme loading in the shortest time.The binding of two well-characterized and stable enzymes, alliinase and l-lactate dehydrogenase, was used to demonstrate the efficacy of the approach. The enzymes were either immobilized directly using a covalent coupling or fixed through a sugar–lectin moiety.

The method has several advantages. First, the enzymes can be immobilized under physiological conditions, which is important for potential in vivo applications. Second, it is possible to produce multiple layers of enzymes, which would create a more resilient biosensor or a reactor with a higher turnover.Third, the protein layers are renewable and the device can be reused.

Michael Keusgen and colleagues at the University of Bonn found that sodium could readily produce carbon–carbon double bonds on the PTFE surface, forming a black membrane. The carbon bonds were then quickly converted into oxygen-bearing functional groups, yielding a white membrane to which other compounds could be attached. The sodium treatment operated overnight, whereas oxidation with ozone took only 45 min. This procedure also led to more stable materials than did peroxide oxidation.

Keusgen says that he and his team have now opened the way to the modification of PTFE surfaces with not only enzymes but also antibodies and even whole cells. “We want to transfer our results obtained with PTFE to other plastics in order to make these materials suitable for systems in the field of clinical diagnostics and quality control of food,” he adds.