Influence of Phosphate on the Adsorption/Desorption of Bovine Serum Albumin on Nano and Bulk Oxide Particles
This work consists of four sections: (1) the adsorption behavior of bovine serum albumin (BSA) by three types of oxide nanoparticles (NPs), TiO 2 (50 ± 5 nm), SiO2 (30 ± 5nm), and Al 2O3 (150 ± 5 nm for &agr; type and 60 ± 5 nm for γ type) in deionized water; (2) phosphate adsorption on these oxide NPs and bulkparticles (BPs); (3) influence of phosphate ions on BSA adsorption; and (4) BSA desorption from oxide NPs in phosphate solution. BPs were also used for comparison with NPs. For BSA adsorption in deionized water, the adsorption maxima on oxide particles are controlled by the surface area and hydrogen content, while the adsorption process is primarily induced by electrostatic interaction, hydrophobic interaction, and ligand exchange between BSA and oxide surfaces. With increasing of hydrogen content, the BSA adsorption mechanism switches from a mainly hydrophobic interaction to hydrogen bonding and ligand exchange. Calculations based on surface area and BSA size, suggest that a multilayer of BSA covers &agr;-Al2O3, but only a single layer surrounds the other oxide particle surfaces. BPs lead to greater conformational change of BSA molecules after their adsorption on the surfaces of oxide particles, although NPs adsorbed more BSA than BPs by weight. For phosphate, the adsorption process is mainly governed by the surface charge of the oxides. Strong electrostatic repulsion can prevent the adsorption of phosphate ions on an oxide surface. Meanwhile, a good linear relationship was observed between surface-normalized BSA adsorption maxima and surface charge of the oxides. For the influence of phosphate ions on BSA adsorption, BSA adsorption is suppressed by phosphate ions, while BSA molecules have no influence on phosphate adsorption. The competition between BSA molecules and phosphate ions is regulated by electrostatic interaction, the hydrogen content of the oxides and oxide surface area (especially micropore surface area). The difference of influence between hydrophobic and hydrophilic interactions on BSA adsorption reduces with the increase of phosphate concentration. Moreover, quantification was employed to calculate the displacing amount of phosphate ions to BSA molecules in competition. The displacing amount of phosphate ions is regulated by micropore surface area, and shows a good linearity with the hydrogen content. For BSA desorption, the BSA desorption hysteresis is observed for SiO2 NPs due to the high aggregation of this type of NPs. The aggregation of NPs can entrap BSA molecules in the closed interstitial spaces, leading to the BSA desorption hysteresis. For &agr;-Al2O 3 and γ-Al2O3 NPs, the hysteresis is observed only at low BSA concentration due to the influence of BSA molecules and electrostatic repulsion to the suspension of NPs. For TiO2 NPs, no significant hysteresis is observed because of their low aggregation and strong electrostatic repulsion. Phosphate adsorbed amounts remain unchanged within the adsorption and two-cycle desorption, indicating the entrapped BSA molecules may not bond to the oxide NPs.
0768: Environmental science