Adsorption of Fluorescein Dyes on Albumin Microspheres

The surface characteristics of bovine and egg albumin microspheres were examined using four anionic dyes; sodium fluorescein, eosin, erythrosin, rose bengal, and the cationic dye rhodamine B. The adsorption isotherms of the dyes on unloaded albumin microspheres exhibited Langmuir behavior for dilute solutions of rose bengal, erythrosin, and eosin, suggesting monolayer formation in the initial stages of the sorption process. The adsorption capacity of the microspheres for the dyes (k₂) and the affinity constants of the dyes for the microspheres (k₁) were found to depend on both the polarizability and the hydrophobic properties of the dye, presumably reflecting the heterogeneous character of the microsphere surface. Further, the extent of sorption at higher dye concentrations was found to depend on the ability of the dye to form stable aggregates inside the microspheres and on environmental long-range forces acting at these sites. At both low and high dye concentrations, the amount adsorbed to the microsphere surface increased with increasing hy-drophobicity of the dyes. The lowest adsorption was observed for the nonsubstituted dye fluorescein, whereas the most hydrophobic dye used, rose bengal, was completely adsorbed onto the microsphere surface. The data suggest that the bovine albumin microsphere surfaces are highly hydrophobic and less porous than egg albumin microsphere surfaces.