Nanoparticle characterization by DLS—a word of caution

N. Farkas, J.A. Kramar
National Institute of Standards and Technology,
United States

Keywords: nanoparticle, dynamic light scattering, size distribution, polydispersity index


Nanoparticle synthesis and manufacturing are critically dependent on reliable dimensional measurements for the optimization of designed performance for novel commercial and biomedical applications. Dynamic light scattering (DLS) is the method of choice for size measurements in most cases. However, both the mean and distributional DLS measurement results may be unknowably significantly biased by 25 % or more, which often lead to incorrect or unclear interpretation of structure and property relationships of nanoparticle formulations. In this talk, we critically discuss the application of DLS for nanoparticle characterization and provide much-needed clarification for ambiguities in the mean-value practice of commercial DLS software and documentary standards. We address the misleading way DLS size distributions are often presented, that is, as a logarithmically scaled histogram of measured relative quantities. Through the measurement of monomodal nanoparticle samples having an extensive range of sizes and dispersities, we demonstrate that the default outputs of a frequently used DLS inversion method are ill chosen, as they are regularizer-dependent and the mean significantly deviates from the cumulant z-average size. We also investigate the DLS polydispersity descriptors of the distributional quality, whether from inversion or cumulant analysis, and find them to be completely unreliable and misleading, both for monodisperse reference materials and broad-distribution self-assembled nanoparticles. These results are intended to bring essential improvements in existing DLS data interpretation practices and to stimulate reexamination of the role of DLS in nanoparticle characterization.