The Presence of Adsorbed Proteins on Particles Increases Aggregated Particle Sedimentation,as Measured by a Light Scattering Technique

Protein conformational changes are often induced when bound to surfaces and can modulate colloidal stability of protein coated particles in dispersion. We evaluated bovine serum albumin (BSA) adsorbed onto polystyrene particles at room temperature. A z-axis translating laser light scattering device (ZATLLS) measured the sedimentation velocity of protein-coated particles tracking aggregation characteristics compared with non-coated ones. Sedimentation velocities of particles moving in the dispersion, and the resulting viscosity and density of the residual solution following sedimentation determined aggregate size in the dispersion using Stoke's law. Our experiments objectively show that albumin-coated polystyrene forms aggregates. Interestingly, coating particles with protein slows the sedimentation velocity which should correspond to a more dispersed system, but it leads to higher aggregate sizes due to the larger influence of proteins in solution raising solution viscosity. Protein-bound particles were observed to fall out of solution in a more controlled and steady manner compared with uncoated particles.