Immobilized redox mediators for electrochemical [NAD.sup.+] regeneration

The applicability of dissolved redox mediators for [NAD(P).sup.+] regeneration has been demonstrated several times. Nevertheless, the use of mediators in solutions for sensor applications is not a very convenient strategy since the analysis is not reagentless and long stabilization times occur. The most important drawbacks of dissolved mediators in biocatalytic applications are interferences during product purification, limited reusability of the mediators, and their cost-intensive elimination from wastewater. Therefore, the use of immobilized mediators has both economic and ecological advantages. This work critically reviews the current stateof-art of immobilized redox mediators for electrochemical [NAD(P).sup.+] regeneration. Various surface modification techniques, such as adsorption polymerization and covalent linkage, as well as the corresponding [NAD(P).sup.+] regeneration rates and the operational stability of the immobilized mediator films, will be discussed. By comparison with other existing regeneration systems, the technical potential and future perspectives of biocatalytic redox reactions based on electrochemically fed immobilized mediators will be assessed.