Resolving power of dynamic light scattering for protein and polystyrene nanoparticles

Dynamic light scattering (DLS) is a non-invasive, label-free technique for the characterization of particles ranging from nanometer to micrometer size. It is widely used for the analysis of proteins to assess association states and the nature of protein aggregates. Despite its frequent use, little quantitative information on its size resolution capabilities, in particular for protein material, is available. This study explores the resolving power of a standard DLS setup for binary mixtures of latex standard particles and mixtures of protein monomer and protein particles made from cross-linked protein material. At constant instrument settings, the resolving power depends on the size ratio and the mass ratio of the species in a mixture as well as on the total concentration and the scattering characteristics of the material. In this study, we provide a summary at which parameter combinations resolution of two species with varying size is possible. These data guide the quantitative evaluation of DLS results for mixtures. We found that a mixture of an antibody monomer and protein particles of an average hydrodynamic diameter of 50 nm can be resolved at a 1-20-fold excess of monomer (by mass). A mixture of monomer and 70 nm particles can be resolved at a 2-30-fold excess, a mixture of monomer and 190 nm particles at a 200-1700-fold excess of monomer. The findings allow to better judge DLS results for protein samples of unknown composition.