Peptide self-assembly as a strategy for facile immobilization of redox enzymes on carbon electrodes

Redox–enzyme-mediated electrochemical processes such as hydrogen production, nitrogen fixation, and CO₂ reduction are at the forefront of the green chemistry revolution. To scale up, the inefficient two-dimensional (2D) immobilization of redox enzymes on working electrodes must be replaced by an efficient dense 3D system. Fabrication of 3D electrodes was demonstrated by embedding enzymes in polymer matrices. However, several requirements, such as simple immobilization, prolonged stability, and resistance to enzyme leakage, still need to be addressed. The study presented here aims to overcome these gaps by immobilizing enzymes in a supramolecular hydrogel formed by the self-assembly of the peptide hydrogelator fluorenylmethyloxycarbonyl-diphenylalanine. Harnessing the self-assembly process avoids the need for tedious and potentially harmful chemistry, allowing the rapid loading of enzymes on a 3D electrode under mild conditions. Using the [FeFe] hydrogenase enzyme, high enzyme loads, prolonged resistance against electrophoresis, and highly efficient hydrogen production are demonstrated. Further, this enzyme retention is shown to arise from its interaction with the peptide nanofibrils. Finally, this method is successfully used to retain other redox enzymes, paving the way for a variety of enzyme-mediated electrochemical applications.