Determining the Number Concentration of Gold Nanoparticles by SAXS

Introduction

Nanoparticles have emerged as a keystone in developing advanced materials and technologies, mainly because of unique properties arising from their diminutive size. Their use and incorporation into various systems can lead to significant improvement of the mechanical, optical or conductive properties. The widespread application of nanoparticles has also emphasized the need for precise characterization and quantification, in particular the accurate determination of the size, the shape and the concentration in nanoparticle dispersions.
Various methods can be used for determination of the nanoparticle number concentration, including dynamic light scattering (DLS) and particle tracking analysis (PTA). However, only small-angle X-ray scattering (SAXS) and single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) are traceable respective to number concentration directly to a SI unit (metre for SAXS, kilogram for sp-ICP-MS). As a result, only these two methods are directly connected to the respective SI-unit via a continuous series of comparisons.(1)
SAXS is a well-established, non-destructive technique for accurately determining the particle size and size distribution.(2-4) Recent advancements have enabled the determination of the traceable determination of nanoparticle number concentrations in dispersions using synchrotron and laboratory SAXS measurements, which has eventually led to the development of an ISO standard on this methodology.(1,5)
Here, we discuss the precise determination of the concentration of gold nano-particles using a laboratory SAXS instrument. Thanks to its optimized design and highly brilliant X-rays, reliable and traceable number concentration results were obtained. In particular, the instrument could provide precise, well analyzable results even from highly diluted particle dispersions.

References

1. Schavkan A, Gollwitzer C, et al. Number concentration of gold nanoparticles in suspension: SAXS and spICPMS as traceable methods compared to laboratory methods, Nanomaterials, 9(4), 502 (2019).
2. Pauw B R, Kästner C, Thünemann A F. Nano-particle size distribution quantification: results of a small-angle X-ray scattering inter-laboratory comparison, J. Appl. Cryst. 50, 1280-1288 (2017).
3. Particle size analysis – Small-angle X-ray scattering (SAXS), ISO 17867:2020.
4. The SAXS Guide, 5th ed. (Anton Paar, 2023).
5. Determination of particle concentration by small-angle X-ray scattering (SAXS), ISO 23484:2023.