From Theory to Real-World Precision - Performing Nanometer-Scale Measurements

Laser diffraction is a well-established technique for determining particle size distributions across a wide range—from the submicron to the millimeter scale. However, achieving accurate and reliable measurements in the nanometer range, particularly below 1 μm, presents a significant challenge. This is primarily due to the fundamental physics of light scattering: smaller particles scatter light at much lower intensities, making it difficult to distinguish subtle differences in size. In this size range, traditional laser diffraction setups often struggle with sensitivity and resolution. Additionally, the optical parameters of the sample, which are required to use the Mie theory for the calculation of the particle size distribution, have a tremendous influence on the results. [1]
The Litesizer DIF addresses these challenges with a unique optical design, specifically optimized for high-resolution measurements in the submicron range. A key feature is its high-intensity blue laser, which, due to its shorter wavelength, enhances the system’s sensitivity to small particles. Additionally, the laser is positioned at an angle rather than aligned horizontally—an important design choice that expands the range of detectable scattering angles. This geometry allows the instrument to more effectively capture the subtle scattering patterns characteristic of nanoparticles, resulting in improved accuracy and resolution down to sizes of 100 nm and less.
And how does laser diffraction compare to other nanoparticle sizing techniques? Dynamic light scattering (DLS) is often the go-to technique for measuring particles in the nanometer range due to its simplicity and sensitivity. It provides intensity-weighted data and is best suited for monomodal, spherical, and low-polydispersity samples. Anton Paar´s Litesizer DLS series offers precision DLS, ELS, and SLS measurements, besides the patented refractive index measurements. Furthermore, the high-end instrument DLS 701 is also capable of performing particle concentration (PCON) and multi-angle DLS measurements (MAPS), enabling analysis of complex and multimodal samples with increased resolution. In summary, the Litesizer DLS is much more than just a particle sizing instrument.
Another competition in this size range is scanning electron microscopy (SEM), which also offers direct imaging at nanometer resolution. However, it is time-consuming, requires a conductive sample, and is not suitable for particle size analysis in suspensions.
In this report, we demonstrate the capabilities of the Litesizer DIF and the Litesizer DLS to accurately and reproducibly measure nanoparticle samples between 10 nm and 220 nm. While the focus here is on this shared range, it should be noted that DLS is capable of measuring particles as small as 0.3 nm.