SAXS measurements were performed on a set of nanoparticle size reference materials from NIST. The experimental data acquired with ScatterX78were analyzed with the EasySAXS software to determine the nanoparticle size distributions. All results were found to be precise and accurate, and in good agreement with the values given by NIST. Additional tests on multi-modal particle size distributions demonstrated the power of the indirect Fourier transformation approach for data analysis.
The set of NIST reference materials RM 8011, 8012 and 8013 consist of highly dilute (0.005 wt.%) aqueous dispersions of gold nanoparticles with nominal particle sizes of 10, 30 and 60 nm, respectively. Generally these are intended for the evaluation and qualification of methodology and/or instrument performance related to the physical/dimensional characterization of nanoscale particles used in pre-clinical biomedical research. The reference materials were used to validate experimental SAXS data acquired with ScatterX78 and analyzed with the EasySAXS analysis software.
The set of NIST reference materials RM 8011, 8012 and 8013 consist of highly dilute (0.005 wt.%) aqueous dispersions of gold nanoparticles with nominal particle sizes of 10, 30 and 60 nm, respectively. Generally these are intended for the evaluation and qualification of methodology and/or instrument performance related to the physical/dimensional characterization of nanoscale particles used in pre-clinical biomedical research. The reference materials were used to validate experimental SAXS data acquired with ScatterX78 and analyzed with the EasySAXS analysis software.
SAXS data were acquired on the Empyrean platform configured with ScatterX78 in combination with a focusing X-ray mirror and the PIXcel3D detector used in 1D mode. The liquid samples were loaded in a disposable quartz capillary and measured under ambient conditions. For the background measurement the capillary filled with water was used. The measurement time per sample was only 20 min. Data reduction and analysis were done with the EasySAXS software. For particle size analysis an indirect Fourier transformation approach was used, yielding volume-weighted size distributions. The particle shape was assumed to be spherical. No a priori assumptions were made about the shape and modality of the size distribution curve.
The figures below show the measurement data from the three colloidal dispersions and of the corresponding background, together with the background-corrected data. The deduced particle size distributions are shown on the right side and the back-transformed data (green lines in the left graphs) are compared with the experimental data. All deduced particle size distributions (blue lines in the right graphs) show a clear maximum, pointing to well-defined, narrow distributions that can be well approximated by a Gaussian (dashed red lines). The minor oscillations next to the main maximum of the distribution have no physical meaning and are unavoidable, known artifacts from the Fourier transformation.
The volume-averaged particle sizes determined from the experimental data are all in good agreement with the values given by NIST (see table).
Additional performance tests were done on various mixtures of the reference materials. As an example, the graph on the right shows a trimodal particle size distribution that could be obtained from the analysis of SAXS data measured from a 1:1:1 mixture of all three samples. Here the three distinct size fractions could be very well resolved. The indirect Fourier transformation is particularly useful for multi-modal size distributions, because no a priori assumptions about the shape and modality of the distribution have to be made.
| Particle diameter (nm) | NIST
RM 8011 | NIST
RM 8012 | NIST
RM 8013 |
|---|---|---|---|
| Experimental | 9.0 | 26.0 | 54.4 |
| NIST | 9.1 +/- 1.8 | 24.9 + /- 1.2 | 53.2 +/- 5.3 |
ScatterX78 delivers high-quality SAXS data within short measurement times, even from highly dilute colloidal dispersions. The performance of the experimental SAXS setup and of the EasySAXS data analysis software were successfully validated against the particle size reference materials from NIST. The indirect Fourier transformation method used for data analysis is particularly powerful to reveal multi-modal nanoparticle size distributions.
