Development of both documentary standards and reference materials is essential for nanotechnology stakeholders: researchers, who need to calibrate or verify their measuring instruments; industry, who must compete with their products in national and international markets and comply with relevant regulations; governments, who need to provide or interpret regulatory requirements; and consumers, who would like to know what their products contain.
In this study, we summarise the contribution made by the National Measurement Institute (NMI) over the past five years to the development of four certified silica nanoparticle reference materials (IRMM FD 100, FD 304, FD 102 and FD 102b). We also discuss NMI’s participation in work carried out in Technical Committee 229 “Nanotechnologies” of the International Organization for Standardization (ISO) that aims to develop validated protocols for the measurement of primary particle size distributions by transmission electron microscopy (TEM) and will lead to a corresponding ISO standard. NMI’s involvement here has focused on silica (analysed using TEM and atomic force microscopy as well as several ensemble techniques), gold nanorods and titania samples (TEM analysis only).
We discuss the challenge of measuring the dimensional properties of many thousands of individual particles to achieve statistical relevance, the influence of image analysis parameters and their effects on the measurement uncertainty, and the challenges of measuring non-spherical particles. We discuss the issue of method divergence, i.e., differences in measurement results between different measurement techniques, and provide insight into measurement uncertainty contributions arising from a number of different influence factors.