Recent activity of international comparison for nanoparticle size measurement

Nanoparticle sizing is the most fundamental measurement for producing nanomaterials, evaluation of nanostructure, and the risk assessment of nanomaterials for human health. Dynamic light scattering (DLS) is widely used as a useful and convenient technique for determining nanoparticle size in liquid; however, the precision of this technique has been unclear. Some international comparisons are now in progress to verify the measurement accuracy of nanoparticle sizing, as a typical example of Asia Pacific Metrology Programme Supplementary Comparison. In this study, we evaluated the precision of DLS technique for nanoparticle sizing and estimated the uncertainty of the DLS data for polystyrene latex suspensions. The extrapolations of apparent diffusion coefficients to infinite dilution and to lower angles yielded more precise values than those obtained at one angle and one concentration. The extrapolated particle size measured by DLS was compared to the size determined by differential mobility analyzer (DMA), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Before the comparison, the intensity-averaged size measured by DLS was recalculated to the number-averaged size, and the thickness of water layer attaching on the surface of particles were added into uncertainty of particle sizing by DLS. After the recalculation, the consistent values of mean particle diameter were obtained between those by DLS and by DMA, AFM, and SEM within the estimated uncertainties.