Counting small particles in electron microscopy images – proposal for rules and their application in practice

Electron microscopy (EM) is the gold standard for characterisation of the morphology (size and shape) of nanoparticles. A direct visual observation of objects under examination is always a necessary first step in the characterisation process. Several questions arise when trying to iden-tify, count and measure the size and shape distribution of nanoparticles and other small particles with EM. In addition to challenges with the dispersion and identification of the particles, there is no unique broadly accepted protocol for counting particles. Here, we focus on counting particles in EM micrographs, as this influences the measurement accuracy of the number of particles im-plicitly affecting the size values of the counted particles. We describe four different, commonly used options for the counting, and propose a naming convention for the counting rules, which are tested in practice in case studies. The impact on the final particle size distribution is high-lighted. One main aim of this analysis is to support the application of a specific, well-defined counting approach in accordance with regulatory requirements, to contribute to achieving more reliable and reproducible results. It is also useful for the forthcoming OECD Test Guideline on Particle Size Distribution for Nanomaterials.

BRESCH Harald;  HODOROABA Vasile-Dan;  SCHMIDT Alexandra;  RASMUSSEN Kirsten;  RAUSCHER Hubert; 

2022-07-18

MDPI

JRC129127

2079-4991 (online),   

https://www.mdpi.com/2079-4991/12/13/2238,    https://publications.jrc.ec.europa.eu/repository/handle/JRC129127,   

10.3390/nano12132238 (online),