Effects of cosolvents and pH on protein adsorption on polystyrene latex: Adynamic light scattering study

Dynamic light scattering was used to study the adsorption of two proteins w ith different surface properties (IgG and HSA) on negatively charged polyst yrene latex. The proteins were adsorbed from water and from water/methanol and water/glycerol mixtures at various pH. Some striking differences betwee n the adsorption behaviors of the proteins were observed. Whereas the thick ness of the adsorbed layer of HSA was extremely sensitive to pH and solvent composition, that of IgG was not. IgG mainly showed an end-on orientation on polystyrene whereas several different surface orientations are suggested for HSA under different conditions. The addition of methanol inhibited the adsorption of HSA on the latex, but it did not affect the adsorption of Ig G. In contrast, the addition of glycerol increased the thickness of the ads orbed layers of both proteins. So, the orientation of IgG on the latex is i nsensitive to pH but is a function of the kind of solvent whereas both pH a nd solvent strongly affect the adsorption of HSA. This is a puzzling result since both cosolvents should equally affect the adsorption of both protein s if the dominant forces for adsorption are the same. Therefore, we conclud ed that, whereas hydrophobic interactions are the dominant force in the ads orption behavior of HSA, van der Waals forces are the main forces involved in the attachment of IgG to the lattices. (C) 2000 Academic Press.