A schematic illustration of "protein corona" formed on the surface of AuNPs upon protein adsorption. The size of the protein corona varies depending on the type and the size of the proteins adsorbed to the AuNPs. As indicated, the adsorption of a protein complex or oligomer will cause larger nanoparticle size increase than an individual protein monomer. The protein-AuNP interaction may also cause AuNP cluster formation if multiple binding sites are present on a protein or protein complex. These differences can be readily detected and discerned according to the dynamic light scattering measurement.