Controlled Release of Proteins Bound to Spherical Polyelectrolyte Brushes

Abstract

Polyelectrolyte Brushes / Protein / Adsorption / Albumin / CounterionsWe discuss the interaction of proteins dissolved in aqueous solution with spherical polyelectrolyte brushes (SPB). The SPB consist of a solid core particle of colloidal dimensions (ca. 100 nm in diameter) onto which long polyelectrolyte chains have been grafted. Immersed in aqueous solution of proteins these SPB will take up high amounts of protein if the ionic strength is low. At high ionic strength, however, virtually no protein will enter into the brush layer attached to the surface of the core particles. We show that bovine serum albumin (BSA) bound at low ionic strength will gradually be released upon raising the salt concentration in the solution in a well-controlled manner: For each raise of the ionic strength in solution there is a well-defined amount of protein that is released. We show that BSA adsorbed to a conventional carboxylated latex will not be released if treated in the same manner. All findings, namely the uptake of protein as well as the controlled release can be explained by the "counterion release force": Patches of positive charge on the surface of the proteins which are immersed in the brush layer become multivalent counterions of the polyelectrolyte chains thus releasing a concomitant number of counter-and coions. Release of counterions as induced by the adsorption of proteins is hence the main driving force for the polyelectrolyte-mediated protein adsorption (PMPA).

Supramolecular Structures Generated by Spherical Polyelectrolyte Brushes and their Application in Catalysis

“…[59] Moreover, a recent study using BSA could demonstrate that this release proceeds in steps if the salt concentration is raised stepwise. [54] This finding underscores the intimate relation between the PMPA and the electrostatic interaction between the PE chains and the surface of the protein.…”

“…[57] Raising the ionic strength leads to a release of most of the adsorbed protein. [54,58] Hence, the SPB can be viewed upon as ''nanoreactors'' that can be charged or decharged with the catalyst. [59] Moreover, a recent study using BSA could demonstrate that this release proceeds in steps if the salt concentration is raised stepwise.…”

“…[54,65] We consider the immersion of a single protein from solution as shown in Figure 10 and enumerate the net release of counterions in this process. Because pH > pI, the number N À of negatively charged groups on its surface is slightly greater than N þ , the number of positively charged groups on the surface.…”

Protein immobilization and separation using anionic/cationic spherical polyelectrolyte brushes based on charge anisotropy

“…While it was higher than that of blank SPB PAA in the pH range from 7 to 3 because the net negative charge of SPB PAA is partially neutralized by adsorbed BSA. 43,56,57 The increase of zeta potential of SPB by BSA adsorption reaches a plateau at pH around 4 where the strongest electrostatic interaction between BSA and SPB PAA takes place. The number of protein molecules interacting with each polyelectrolyte chain of SPB increases at this pH, thus leading to the charge neutralization of BSA-SPB PAA complexes.…”

Poly-acrylic Acid Brushes and Adsorbed Proteins

“…Most prominent is the effect of the ionic strength of the dispersing medium which can alter a brush system from protein adsorbing to protein repellant [9]. A widely studied model, and quantitatively analyzed for both spherical (SPB) and planar polyelectrolyte brushes (PPB), is the adsorption of bovine serum albumin (BSA) to polyacrylic acid (PAA) brushes [10][11][12][13][14][15][16][17][18][19][20][21][22]. Here, the amount of immobilized BSA depends on the external parameters pH, ionic strength and protein concentration of the aqueous liquid phase and, in addition, on the internal parameters grafting density and PAA chain length.…”