Towards reproducible measurement of nanoparticle size using dynamic light scattering:Important controls and considerations

The characterization of nanoparticles in dispersions, in particular measuring their size and size distribution, is a prerequisite before they can be used in toxicological testing. Such characterization requires reliable methods with good reproducibility. The aim of this study was to evaluate the reproducibility, and thus the potential of Dynamic Light Scattering (DLS) for nanoparticle size determination. DLS is easy to use and well established in most nanotoxicology laboratories. However, reproducibility and in particular variability between measurements done using different instrumental setups have not been addressed systematically before. Here we performed initial experiments with rather monodisperse dispersions of spherical particles in water. Significant discrepancies in the measured distributions were obtained with different DLS instruments, especially when fitting the data using mathematical inversion methods. Significant errors can be made due to different settings being used for fitting the data. These were even more prominent when working with dilute dispersions of very small particles. Our study has identified several important points to be taken into consideration in order to overcome possible issues in measurement and analysis of nanoparticles using DLS. In practice, however, nanoparticles may have significant polydispersities and/or can be non-spherical. We extend the comparative work on spherical particles, to show how to characterize polydisperse and/or high aspect ratio particles using DLS instruments.