Effect of Sample Concentration on Nanoparticle Tracking Analysis of Small Extracellular Vesicles and Liposomes Mimicking the Physicochemical Properties of Exosomes

For quantitative analysis, data should be obtained at a sample concentration that is within the range of linearity. We examined the effect of sample concentration on nanoparticle tracking analysis (NTA) of small extracellular vesicles (sEVs), including exosomes, by comparing NTA results of sEVs with those obtained for polystyrene nanoparticles (PSN) and liposomes, which mimic lipid composition and physicochemical properties of exosomes. Initially, NTA of PSN at different concentrations was performed and the particle sizes determined were validated by dynamic light scattering. The major peak maxima for PSN mixtures of different sizes at the higher particle numbers were similar, with some fluctuation of the minor peak maxima observed at the lower particle number, which was also observed for sEVs. Sample concentration is critical for obtaining reproducible data for liposomes and exosomes and increasing the sample concentration caused an increase in data variability because of particle interactions. The inter-day repeatability of particles sizes and concentration for sEVs were 7.47 and 4.51%, respectively. Analysis of the linearity range revealed that this was narrower for sEVs when compared with that of liposomes. Owing to the use of liposomes that mimic the lipid composition and physicochemical properties of exosomes and proteinase-treated sEVs, it was demonstrated that these different analytical results could be possibly caused by the protein corona of sEVs. Consideration of the sample concentration and linearity range is important for obtaining reproducible and reliable data of sEVs.