Synthesis and Characterization of PEG-Modified Polystyrene Particles and Isothermal Equilibrium Adsorption of Bovine Serum Albumin on these Particles
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A series of monodisperse submicron polystyrene (PS) particles with different surface monomethoxy poly(ethylene glycol) (mPEG) densities were prepared and characterized. The effects of the chemically grafted mPEG chains (MW = 2,000) on the adsorption of bovine serum albumin (BSA) molecules onto these negatively charged particles at pHs 5 and 3 were investigated. The native particles at both pH values showed the largest values of q max (maximum amount of BSA adsorbed on the particle surface). The surface mPEG chains were very effective in retarding the BSA adsorption and q max decreased significantly with increasing surface mPEG density. The values of q max were greater for both the native and mPEG-modified particles at pH 5 compared to those counterparts at pH 3, due to the different adsorption mechanisms. Hydrophobic interaction predominated in the adsorption of BSA molecules on the particles at pH 5, whereas electrostatic interaction had a crucial influence on the BSA adsorption at pH 3. At pH 5, the adsorption behaviors were qualitatively explained by the calculated values of the free energy barrier against the BSA adsorption. A schematic model was also proposed to qualitatively describe the conformations of BSA molecules adsorbed on the particle surfaces.
Key wordsBSA electrostatic interaction hydrophobic interaction PEG-modified PS particles protein adsorption steric hindrance effect
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