Reliable size determination of nanoparticles using dynamic light scattering method for in vitro toxicology assessment

Dynamic light scattering (DLS) is widely used for the evaluation of the particle size in the toxicity assessment of nanoparticles. However, the many types of DLS instruments and analytical procedures sometimes give different apparent sizes of particles and make it complicated to understand the size dependence on particles for the toxicity assay. In this study, we established an evaluation method of secondary nanoparticle sizes using a DLS analysis. First, we established a practical method for determining size with an appropriate evaluation of uncertainties. This proposed method could be a universal protocol for toxicity assessment that would allow researchers to achieve some degree of concordance on the size of nanoparticles for an assessment. Second, we investigated the processes associated with particles in suspension by examining the changes in the size and the light scattering intensity of secondary nanoparticles during an in vitro toxicity assessment, since the transport mode of particles to cells is significant in understanding in vitro nano-toxicity. In this study, these two points were investigated on TiO2 nanoparticles suspension as an example. The secondary particles of TiO2 with a light scattering intensity-averaged diameter (dl) of 150–250 nm were characterized with appropriate uncertainties. The sizes were found to be comparable with values determined using other analytical procedures and other instruments. It is suggested that dl could be an effective size parameter for toxicity assessments. Furthermore, TiO2 secondary nanoparticle suspensions are well dispersed with slow gravity settling, no agglomeration, with the diffusion process as the primary transport mode of particles to cells.