Improving the environment for immobilized dehydrogenase enzymes by modifying Nafion with tetraalkylammonium bromides

Recent research in our group has shown that mixture-casting Nafion with quaternary ammonium bromides can increase the electrochemical flux of redox couples through the membrane and allow for larger redox species to diffuse to the electrode surface. The research has also suggested that when these salts are cast with Nafion micellar pore size is changing. Therefore, it was proposed that the quaternary ammonium salts could be employed to tailor the structure of the Nafion membrane for immobilizing enzymes in the polymer. For cations with a high affinity for the sulfonic acid groups of Nafion, the modified structure of Nafion can also help to stabilize the enzyme and increase activity by providing a protective outer shell and an ideal chemical environment that resists a decrease in pH within the pore structure. This research examines the ability to immobilize dehydrogenase enzymes in Nafion that has been modified with quaternary ammonium bromides. Fluorescence assays, fluorescence microscopy, and cyclic voltammetric studies were employed to analyze the ability to immobilize an enzyme within the membrane, to determine the activity of the immobilized enzyme and to examine the transport of coenzyme within the membrane. Dehydrogenase enzymes immobilized in tetrabutylammonium bromide/Nafion membranes have shown high catalytic activity and enzyme active lifetimes of greater than 45 days. A variety of dehydrogenase enzymes have been successfully immobilized in the membrane, including: alcohol dehydrogenase, aldehyde dehydrogenase, glucose dehydrogenase, and lactic dehydrogenase.