Electrified Nanoconfined Biocatalysis with Rapid Cofactor Recycling

In living cells, the overall rates of catalytic reaction chains (cascades) are massively enhanced by nanoconfinement of enzymes in tiny enclosed volumes: presented in such a way, interdependent catalysts are highly concentrated, and distances (active site‐to‐active site) across which intermediates and cofactors must diffuse, may be tiny. In a parallel technology exploiting this principle, enzyme cascades are powered, amplified, and monitored in real time as they work in concert, being nanoconfined within the pores of an electrically conductive metal oxide electrode. The technology, nicknamed the electrochemical leaf, mimics chloroplast biosynthesis by exploiting nicotinamide adenine dinucleotide (NADP(H)) recycling catalysed by the flavoenzyme, ferredoxin NADP+ reductase (FNR). Adsorbed on the inner walls of the nanopores, FNR rapidly transfers electrons between the electrode and NADP(H). This activity is coupled to an oxidoreductase enzyme, also nanoconfined within the pores, which recycles the cofactor and selectively synthesises a desired product or senses an analyte. Use of catalyst and cofactor is very efficient. The technology is simple, inexpensive and adaptable, and scalable to both microscopic levels (diagnostics) and macroscopic levels (organic synthesis). Whereas native FNR is specific for NADP(H), the technology can be extended by genetic engineering to include NAD(H) as recycling cofactor. The electrochemical leaf: represented here as a sheet of titanium foil coated each side with a micron‐scale conductive layer of indium tin oxide nanoparticles, at which whole enzyme cascades are assembled and trapped in the nanopores. The electrochemical leaf provides a powerful new way to synthesise complex organic molecules. The technology, which embodies fast and efficient NAD(P)(H) cofactor recycling within electrode nanocavities, allows biocatalysis to be investigated and exploited with unprecedented ease.