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The conformation of polyzwitterionicbrushes plays a crucial rolein the adsorption/desorption of proteins on solid surfaces. By useof quartz crystal microbalance with dissipation (QCM-D) and surfaceplasmon resonance (SPR), we have systematically investigated the conformationalbehavior of poly(sulfobetaine methacrylate) (PSBMA) brushes as a functionof ionic strength in the presence of different ions. The frequencychange demonstrates that the effectiveness of anions to weaken theinter/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 highionic strengths. The dissipation change indicates that some heterogeneousstructures are formed inside the brushes in the presence of chaotropicanions with the increase of ionic strength. In SPR studies, the changeof resonance unit (ΔRU) with ionic strength is determined bythe balance between the increase of thickness and the decrease ofrefractive index of the brushes. No anion specificity is observedin the SPR measurements because ΔRU is insensitive to the coupledwater molecules inside the brushes. For the control of protein adsorption/desorption,our studies show that the brushes can more effectively resist theprotein adsorption in the presence of a more chaotropic anion anda more chaotropic anion can also more effectively induce the proteindesorption from the surface of the brushes. In addition, no obviouscation specificity can be observed in the conformational change ofthe brushes in either QCM-D or SPR measurements. [ABSTRACT FROM AUTHOR]

We have systematically investigated the effect of surfacewettabilityon ion-specific adsorption of bovine serum albumin (BSA) by usingquartz crystal microbalance with dissipation (QCM-D) and surface plasmonresonance (SPR). The changes in frequency (Δf) and resonance unit (ΔRU) show a nonmonotonous change of theadsorbed amount of BSA as a function of molar fraction of 1-dodecanethiol(xDDT) of the self-assembled monolayerat pH 3.8, while the amount of adsorbed protein gradually increaseswith the xDDTat pH 7.4. The small changesof dissipation (ΔD) indicate that BSA moleculesform a quite rigid protein layer on the surfaces, which results inonly a slight difference in the adsorbed mass between the mass-uptakeestimations from the Sauerbrey equation and the Voigt model. The differencein the adsorbed mass between QCM-D and SPR measurements is attributedto the coupled water in the protein layer. On the other hand, specificanion effect is observed in the BSA adsorption at pH 3.8 with theexception of the surface at xDDTof 0%,but no obvious cation specificity can be observed at pH 7.4. The ΔD–Δfplots show that the BSAadsorption at pH 3.8 has two distinct kinetic processes. The firstone dominated by the protein–surface interactions is an anion-nonspecificprocess, whereas the second one dominated by the protein structuralrearrangements is an anion-specific process. At pH 7.4, the secondkinetic process can only be observed at the relatively hydrophobicsurfaces, and no cation specificity is observed in the first and secondkinetic processes. [ABSTRACT FROM AUTHOR]