Small Angle Neutron Scattering Study of Fractal Structure of Oppositely Charged Nanoparticle and Protein Complexes

The structure of complexes of oppositely charged anionic silica nanoparticles and cationic lysozyme protein in aqueous solutions has been studied by small-angle neutron scattering. The measurements have been carried out for three different sized silica nanoparticles (9.4, 17.4 and 28 nm) at their fixed concentration (1 wt%) while varying the concentration of lysozyme protein in the range 0-5 wt%. The protein adsorption on the nanoparticles is governed by the attractive electrostatic interaction between nanoparticle and protein, which in turn lead to the aggregation of nanoparticles mediated by proteins. These aggregates are characterized by the fractal structure. The amount of adsorption and the evolution of fractal structure have been found to be strongly depending on the protein concentration and nanoparticle size.