Ion-Specific Conformational Behavior of Polyzwitterionic Brushes: Exploiting It for Protein Adsorption/Desorption Control

The conformation of polyzwitterionic brushes plays a crucialrole in the adsorption/desorption of proteins on solid surfaces. By use ofquartz crystal microbalance with dissipation (QCM-D) and surfaceplasmon resonance (SPR), we have systematically investigated theconformational behavior of poly(sulfobetaine methacrylate) (PSBMA)brushes as a function of ionic strength in the presence of different ions. Thefrequency change demonstrates that the effectiveness of anions to weakenthe inter/intrachain association and to enhance the hydration of the graftedchains increases from kosmotrope to chaotrope in the low ionic strengthregime, but the ordering of anions is almost reversed at the high ionicstrengths. The dissipation change indicates that some heterogeneousstructures are formed inside the brushes in the presence of chaotropic anions with the increase of ionic strength. In SPR studies,the change of resonance unit (ΔRU) with ionic strength is determined by the balance between the increase of thickness and thedecrease of refractive index of the brushes. No anion specificity is observed in the SPR measurements because ΔRU is insensitiveto the coupled water molecules inside the brushes. For the control of protein adsorption/desorption, our studies show that thebrushes can more effectively resist the protein adsorption in the presence of a more chaotropic anion and a more chaotropicanion can also more effectively induce the protein desorption from the surface of the brushes. In addition, no obvious cationspecificity can be observed in the conformational change of the brushes in either QCM-D or SPR measurements.