Design principles for a nanoconfined enzyme cascade electrode via reaction-diffusion modelling.

The study of enzymes by direct electrochemistry has been extended to enzyme cascades, with a key development being the 'electrochemical leaf': an electroactive enzyme is immobilized within a porous electrode, providing in situ cofactor (NADP(H)) regeneration for a co-immobilized downstream enzyme. This system has been further developed to include multiple downstream enzymes, and it has become an important tool in biocatalysis, however, the local environment within the porous electrode has not been investigated in detail. Here, we constructed a 1D reaction-diffusion model, comprising the porous electrode with 2 kinds of enzymes immobilized, and an enzyme-free electrolyte diffusion layer. The modelling results show that the rate of the downstream enzyme is a key parameter, and that substrate transport within the porous electrode is not a main limiting factor. The insights obtained from this model can guide future rational design and improvement of these electrodes and immobilized enzyme cascade systems.