Nanoparticles belong to the class of nanomaterial that are natural, incidental, or manufactured materials containing elementary particles where at least one external dimension is in the range of 1 nm to 100 nm for 50% or more of the particles in the number size distribution. Therefore, size criteria is a key control parameter for defining nanoparticles. Moreover, nanoparticles have the property of assembling, agglomerating, or aggregating elementary particles into larger entities. But, the definition clearly refers to elementary particle and thus fine methodology must be used to obtain the critical size of nanoparticles. Besides, nanotoxicology which is the field of study of toxicological effect of nanoparticle in health aims to relate putative toxicological effect to the size of nanoparticles as the current dogma in the field suggest a greatest impact/reactivity with smaller particles than larger ones. Thus, obtaining accurate size measurements of nanoparticles is of great scientific significance.

In this work, we have combined several biophysical and microscopic methods to characterize the size of several nanoparticles of main interest in toxicological studies. Although we have worked on more than 50 different metallic nanoparticles, we only focused our interest on two families: Silver (Ag) and titane oxide (TiO₂). We have used atomic force microscopy, wet scanning transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering. First, controls on well-behaved nanosize samples were performed and maximum dispersion between low-bound and high-bound sizes was about 30%. The striking results of this work is the relatively large dispersion of results obtained on Ag and TiO₂ (several hundreds of percent) depending on the method used. Several hypotheses can explain these results: nanoparticle solutions are highly heterogeneous and some methods may capture different forms, measurement methods are biased toward a certain size, methodologies used to extract sizes are inaccurate. All these hypotheses are plausible and will be discussed in this work.

Figures:

Size measurement of the same batch of silver nanoparticles with different methods. Methods 1 indicate values of elementary particles whereas methods 2 indicate those of agglomerated particles.

Size measurement of the same batch of titane oxide nanoparticles with different methods. Methods 1 indicate values of elementary particles whereas methods 2 indicate those of agglomerated particles.

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EMC Abstracts - https://emc-proceedings.com/abstract/heterogeneity-in-nanoparticle-size-determination-using-several-biophysical-and-microscopy-methods/