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

Abstract

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.

Emerging Functional Porous Polymeric and Carbonaceous Materials for Environmental Treatment and Energy Storage

“…Membrane separation is a frequently used energy-efficient tool in water purification, while other separation techniques such as electrochemical separations of redox-electrodes have been successfully developed. [221][222][223][224] The membrane separation process includes microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) according to their pore sizes. MF membranes with large surface pores are capable of removing large particles and microorganisms.…”

An Asymmetric Iron‐Based Redox‐Active System for Electrochemical Separation of Ions in Aqueous Media

“…The PVFc metallopolymer has recently been observed to exhibit redox‐mediated hydrogen bonding that imparts it with the ability to electrochemically separate organic carboxylate anions in both aqueous and organic solution with high separation factors of ≈100 in over 100‐fold excess competing electrolyte, [ 17 ] inorganic oxyanions from wastewater [ 18 ] and nuclear waste, [ 19 ] and even proteins. [ 20 ] As the activation of the redox‐species is mediated by an electrochemical stimulus, the process is reversible and desorption of adsorbed compounds can be accomplished via moderate electrochemical potential swings. This framework for targeted and electrochemically reversible separation has been applied to both organic micropollutants such as pharmaceuticals and personal care products and endocrine disruptors, [ 21 ] which are usually present in the ppt to ppb concentration ranges and inefficiently removed to varying degrees in wastewater plants, [ 22 ] as well as inorganic heavy metal contaminants, which are well‐known for their toxicity and carcinogenicity.…”

Recent Trends in Metallopolymer Design: Redox‐Controlled Surfaces, Porous Membranes, and Switchable Optical Materials Using Ferrocene‐Containing Polymers

“…The voltage swings were shown to be as low as 0.6 V with a two‐electrode setup, and current efficiencies >98 % . The strong interaction of oxidized PVFc‐modified electrodes has also been extended for proteins, presumably interacting with the carboxylate functionalities of the proteins . The interactions and selectivity for proteins were shown to be more complex than that for small molecules, with a dependence based on charge distribution and the isoelectric point.…”