Cluster Morphology of Protein-Coated Polymer Colloids

We report measurements on the aggregation processes in a colloidal suspension of polystyrene particles covered with F(ab')2 (immunoglobulin IgG fragment) performed by static and dynamic light scattering. In order to study the cluster morphology of aggregates, the fractal dimension is obtained from the dependence of the scattered intensity on the scattering wave number. The stability domains of bare and protein-coated polystyrene particles were examined by plotting the stability ratio as a function of electrolyte concentration. The stability results have been explained using a modified Derjaguin-Landau-Verwey-Overbeek theory to describe the interparticle interaction. The observed change in the fractal dimension can be explained by the existence of a minimum separation distance between coagulated particles (restructuring). This minimum distance is attributed to the layer of hydrated ions and water molecules adsorbed on the particle surface. Our results are in agreement with the reversible-growth model of W. Y. Shih, I. A. Aksay, and R. Kikuchi (Phys. Rev. A. 36, 5015 (1987)) and they were supported by transmission electron microscopy observation. Copyright 1998 Academic Press.