Redox Interfaces for Electrochemically Controlled Protein–Surface Interactions: Bioseparations and Heterogeneous Enzyme Catalysis

Redox-active materials are an attractive platform for engineering specific interactions with charged species by electrochemical control. We present nanostructured redox-electrodes, functionalized with poly(vinyl)ferrocene embedded in a carbon nanotube matrix, for modulating the adsorption and release of proteins through electrochemical potential swings. The affinity of the interface toward proteins increased dramatically following oxidation of the ferrocenes, and, due to the Faradaic nature of the organometallic centers, the electrodes were maintained at sufficiently low overpotentials to ensure the preservation of both protein structure and catalytic activity. Our system was selective for various proteins based on size and charge distribution, and exhibited fast kinetics (<120 s for a charge–discharge cycle) and high uptake capacities (>200 mg/g) under moderate overpotentials (+0.4 V vs Ag/AgCl), as well as remarkable stability for binding under ferrocene oxidation conditions. The preservation of bioactivity and protein structure at the interface indicates the potential for these redox-mediated surfaces to be used as heterogeneous supports for enzyme catalysis. This work draws on the molecular selectivity of ferrocene-functionalized materials toward organic anion groups, and demonstrates that these smart redox-active materials can be used for modulation of the macroscopic affinity of surfaces for charged biomacromolecules to enhance processes such as bioseparations, electrochemically controlled protein purification, biocatalysis, and electrochemically mediated drug release.