Polyelectrolyte Brush Electrodes for Protein Capture and Release

Doctoral thesis, 2020

Stimuli-responsive polyelectrolyte brushes switch as a function of pH between a charged and neutral state that affects their electrostatic interactions with other charged molecules like proteins. Adjustment of the pH results in the binding of large quantities of proteins making polyelectrolyte brushes widely used as biointerfaces. However, the interaction between proteins and polyelectrolyte brushes remains poorly understood. Protein binding to brushes despite net repulsion indicates that the mechanism is determined by more than electrostatic effects. In this thesis polyelectrolyte brushes, and protein-polyelectrolyte interactions were characterized using new methods. The results show that non-electrostatic interactions play an important role in protein binding to pH-responsive polyelectrolyte brushes.

Active switching of polyelectrolyte brushes requires control of the pH. However, controlled pH switching that is convenient and non-invasive has proven difficult to achieve. In this thesis electrochemistry was used to generate local pH gradients, that resulted in reversible switches of polyelectrolyte brushes, even in highly buffered liquids and in biological solutions like serum. Reversible electrochemical switching of polyelectrolyte brushes was accomplished by employing diazonium salt surface functionalization. Electrochemical switching was used to control protein-polyelectrolyte interactions to create polyelectrolyte brush electrodes that captured and released high quantities of proteins on-demand. Our method for electronic control of protein immobilization should increase the utility of pH-stimuli-responsive polymer brushes in applications such as bioanalytics, protein purification, and protein drug-delivery.