Protein Identity and Environmental Parameters Determine the Final Physicochemical Properties of Protein-Coated Metal Nanoparticles

When a nanomaterial enters a biological system, proteins adsorb onto the particle surface and alter the surface properties of nanoparticles, causing drastic changes in physicochemical properties such as hydrodynamic size, surface charge and aggregation state, thus giving a completely new and undefined physicochemical identity to the nanoparticles. In the present work, we study the impact of the protein identity (molecular weight and isoelectric point) and the environmental conditions (pH and ionic strength) on the final physicochemical properties of a model nanoparticle system, i.e. gold nanoparticles. Gold nanoparticles either form stable dispersions or agglomerate spontaneously when mixed with protein solutions, depending on the protein and the experimental conditions. Strikingly, the agglomerates redisperse to individually dispersed and colloidally stable nanoparticles, depending on the purification pH. The final protein coated nanoparticles exhibit specific stabilities and surface charges that depend on protein type and the conditions during its adsorption. By understanding the interactions of nanoparticles with proteins under controlled conditions, we can define the protein corona of the nanoparticles and thus their physicochemical properties in various media.