Kinetic investigation of protein adsorption into polyelectrolyte brushes by quartz crystal microbalance with dissipation: The implication of the chromatographic mechanism

Abstract

With the growing concerns of polymer-grafted ion-exchange chromatography, the importance of protein adsorption on charged polymer-grafted surfaces cannot be stressed enough. However, a full understanding in adsorption in polymer brushes is still a great challenge due to the lack of in situ characterization technique. In this work, we use quartz crystal microbalance with dissipation to in situ investigate adsorption kinetics of γ-globulin and recombinant human lactoferrin on poly(3-sulfopropyl methacrylate) (pSPM) sensors prepared via atom transfer radical polymerization. With an increase of chain length and grafting density, great increasing amounts of proteins on pSPM-grafted sensors revealed that protein underwent a transition from monolayer to multilayer adsorption. It was attributed to direct protein binding into charged brushes, in which more binding sites involved and more coupled water lost. However, such a strong binding and rigid structure of proteins limited the protein transport in pSPM brushes and “chain delivery” effect. With an increase in grafting density, moreover, denser brushes hindered adjustment in protein conformation in pSPM brushes and further exacerbated protein transport in pSPM brushes. Furthermore, the influence of buffer pH and salt concentration further validated the ion exchange characteristics of protein adsorption into pSPM brushes. The research provided a variety of in situ evidence of protein binding and conformation evolution in pSPM brushes and elucidated mechanism of protein adsorption in pSPM brushes.