Adsorption of bovine serum albumin onto styrene/acrylic acid copolymer latex

Abstract

The adsorbability of bovine serum albumin (BSA) onto styrene/acrylic acid copolymer (PS/PAA) latex prepared without emulsifier was investigated as a function of pH and ionic strength. Polystyrene (PS) latex was used as a reference sample. The adsorption isotherms of BSA onto PS/PAA latices showed a stepwise nature. The thickness of the adsorbed BSA monolayer suggested that BSA molecules adsorbed onto PS/PAA₂ latex (here, the subscript, i. e., 2, represents the mol % of acrylic acid used in copolymerization) in a “side-on” mode near the isoelectric point (IEP) of this protein. However, in the case of PS/PAA₅ latex, a portion of the BSA molecules probably adsorbed in a “loop” or an “end-on” mode. The amount of BSA adsorbed onto PS/PAA latices greatly depended on pH and ionic strength; its value showed a maximum in the neighborhood of the IEP of BSA as in PS latex. The amount adsorbed onto PS/PAA latices except in the alkaline pH region was greater than that onto PS latex. Moreover, the amount adsorbed onto PS/PAA₅ latex was greater than that onto PS/PAA₂ latex. Both these results are probably attributed to hydrogen bonding between BSA molecule and PS/PAA latex. It was found that the adsorbability of BSA especially at a high ionic strength greatly depended on the surface properties of polymer latices.