Cluster morphology of protein-coated polymer colloids

We report measurements on the aggregation processes in a colloidal suspensi on of polystyrene particles covered with F(ab')(2) (immunoglobulin IgG frag ment) performed by static and dynamic light scattering. In order to study t he cluster morphology of aggregates, the fractal dimension is obtained from the dependence of the scattered intensity on the scattering wave number. T he stability domains of bare and protein-coated polystyrene particles were examined by plotting the stability ratio as a function of electrolyte conce ntration. The stability results have been explained using a modified Dejagu in-Landau-Verwey-Overbeek theory to describe the interparticle interaction. The observed change in the fractal dimension can be explained by the exist ence of a minimum separation distance between coagulated particles (restruc turing). This minimum distance is attributed to the layer of hydrated ions and water molecules adsorbed on the particle surface. Our results are in ag reement 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 transmi ssion electron microscopy observation. (C) 1998 Academic Press.