Dynamic light scattering and electrophoretic light scattering are the techniques available in the Zetasizer range of products to determine the size and zeta potential of a sample. Both techniques and the Zetasizer brand are well established in a variety of fields including nanoparticles characterization, biomedical research, including the exciting gene therapy and vaccine research fields, food and cosmetics as well as in some of our most basic needs such as freshwater treatment.

In a time of an increased variety of challenges, smaller usually means unexplored opportunities. It is then important to be able to closely monitor the size of particles and macromolecules but also to have a measure of the stability for those materials. We have now got to a point in time where commercial light scattering instruments are sensitive enough to characterize nearly any nano-sized material available and that provide us much more than just a size or zeta potential value. Did you know that most of the information you need to understand the quality of your size measurement is provided in the correlogram – including whether dilution might be required or if there are oversized particles in a sample? Or that with the latest advances in the Zetasizer Ultra Red, you can determine the concentration of particles using only size results?

Top 5 tips on the Zetasizer

If as a user, all you are after is a size value or a charge indicator, this may sound like a lot to digest. However, what this means is that there is a lot more information available for those with a more inquisitive mind.

On this free webinar, you will be given tips on how to better understand your DLS and ELS measurements and gain the confidence that the numbers you are reporting are meaningful. To make this webinar useful and time-efficient, we will not be covering a “back to basics” of the two technologies. Therefore, we have included in this blog two short introductory sections and some further reading links that will give a good foundation for the topics covered in the webinar.

A basic Introduction to Dynamic Light Scattering

Dynamic light scattering is a technique that analyzes the fluctuation rates of the intensity of light scattered by particles in a solution to then correlate it into a hydrodynamic diameter.

If particles were static in a solution, the light scattered would be a flat signal which doesn’t change with time. Since particles are undergoing random Brownian motion due to collision with solvent molecules, the intensity of light scattered will fluctuate with time. The smaller a particle is, the greater the effect of the collision with the solvent molecules and therefore the greater their Brownian motion rates, and vice versa. Using the Stokes-Einstein relation, the software can then convert the diffusion rates of the particles into a hydrodynamic diameter.

For more information on this technique please read the technical note: “An Introduction to DLS in 30 minutes”.

A basic introduction to Electrophoretic Light Scattering

Electrophoretic light scattering is the technique that measures the frequency shift of a scattered beam to determine the velocity of particles under an electric field and then convert that information into a Zeta potential value.

When exposed to an electric field, charged particles will respond by moving towards the opposite electrode. The velocity at which these particles move is dependent, among other factors, on the Zeta potential of the sample. We determine this velocity by analysing the Doppler shift, or the frequency shift of a scattered beam, which passes through the cell and comparing it to a reference beam. The difference in phase between the beat frequency and the reference frequency equals the frequency shift. A 1 Hz frequency shift is equivalent to 1 mV of Zeta potential.

You can find a more extensive explanation for this technique on: “Zeta Potential – An Introduction in 30 Minutes

Factors affecting accuracy and precision of the results

Several factors will influence both the accuracy and precision of the measurements. In the live webinar, we will discuss some of these factors and how they may relate to sample preparation and be easily remedied. For example, the concentration, polydispersity or even dispersant inconsistency can all add to lower reproducibility in the results but, most of the time, these can be addressed by the users.

In this Ask an Expert! webinar, we will learn how to better assess some of the plots obtained in DLS and ELS measurements, as well as how to use some of the most important parameters to gain a better understanding of the results you are collecting. Join us on April 8th and send in your questions prior to the webinar. You can do so by emailing askanexpert@malvernpanalytical.com or using the #MPexpert hashtag on Twitter. We can handle some of your questions during the webinar.