Steering protein and salt ad- and desorption by an electrical switch applied to polymer-coated electrodes

Although solid-phase chromatography is a well-established method for protein separation, chemically intensive and often costly regeneration steps are needed to make reuse of the adsorbent possible. Here, we demonstrate the use of electrochemical principles as sustainable alternative. We make use of spontaneous adsorption of proteins to solid electrodes and reverse this process by applying an electric potential to regenerate the interface. This allows for adsorption of proteins to take place at 0 V difference between the electrodes, due to electrostatic interactions between the protein and the electrode surface. The desorption is then triggered by applying a potential difference (−1.2 V) between the electrodes. It is demonstrated that the incorporation of negatively charged polystyrene sulfonate (PSS) or positively charged polydiallyldimethylammonium chloride (PDMAC) in or on top of the respective activated carbon electrodes increases the amount of exchanged protein from 1 to 10 mg g⁻¹, as compared to simple activated carbon electrodes. Interestingly, salt ad- and desorption occurs in opposite cycles compared to protein ad- and desorption, resulting in simultaneous concentration and desalting of the protein when 0 V is applied. On top of that, we also found that an enrichment in β-lactoglobulin could be achieved starting from whey protein isolate. These results clearly demonstrate that electrochemical technologies can be used not only for protein separation (including removal of salt), but also for protein fractionation, while not requiring solvent use.