Protein multilayer formation on colloids through a stepwise self-assembly technique

Multilayer films of the proteins fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) and immunoglobulin G (IgG) were assembled on 640 nm diameter polystyrene (PS) latex particles by their alternate deposition with either positively or negatively charged polyelectrolytes. The proteins and polyelectrolytes were deposited under conditions where they were oppositely charged to one another, thereby facilitating growth of the films through electrostatic interactions. The regular, controlled, stepwise assembly of the protein and polyelectrolyte multilayer films was followed by electrophoretic mobility (EPM), single particle light scattering (SPLS), and transmission electron microscopy (TEM) methods. EPM measurements reveal alternating negative and positive zeta-potentials with deposition of each protein and polyelectrolyte layer, respectively, for the FITC-BSA multilayer films. In contrast, no reversal of the surface charge occurred for the deposition of Ige and poly(sodium 4-styrenesulfonate) (PSS) in the construction of IgG multilayers, although an oscillatory behavior in zeta-potential was observed under the conditions studied. Both SPLS and TEM demonstrate that regular, stepwise protein multilayer growth occurs for both FITC-BSA and IgG. TEM also provides direct visual observation that the PS colloids are uniformly coated with protein. The stepwise. alternate assembly technique employed permits nanometer-level control over the thickness of the protein-polyelectrolyte shell surrounding the colloids. The formation of these novel, biologically functional, core-shell particles is expected to impact the areas of biotechnology and biochemical engineering.