This video will explain the technique of Dynamic Light Scattering or DLS for short.
I'll show you the basics of how DLS works and how you can use it to measure the size of your particles and macromolecules.
DLS measures the Brownian motion of particles in a dispersion
and uses this information to determine their hydrodynamic size I'll explain this term shortly.
Brownian motion is the random movement of particles which results from their collision with solvent molecules
such as water.
Smaller particles move or diffuse more quickly and larger particles diffuse more slowly.
The rate of Brownian motion is quantified as the translational diffusion coefficient which is often represented by capital D
The hydrodynamic size measured by DLS is defined as the size of a sphere that diffuses at the same rate as the particle being measured.
This sphere comprises the core particle plus anything which is bound to its surface for example any ions
or absorbed polymers
so how do we measure diffusion rates using DLS let's take a look
Imagine we illuminateparticles with a laser they'll scatter some of the light that hits them
if these particles were completely still we'd measure a constant intensity of scattered light
however in a dispersion diffusion causes the intensity of light scattered by the particles to fluctuate over time,
it's dynamic.
The detected light scattered from lots of randomly diffusing particles combines to create a fluctuating intensity signal.
The fluctuations are caused by the interference of light scattered by each individual particle
the intensity will change over time as the particles continue to diffuse
the speed of these intensity fluctuations depends on the particles diffusion rate
The smaller the particle the more quickly it diffuses
which translates to more rapid fluctuations in scattered light and vice-versa.
So we've explained how Brownian motion affects dispersed particles of different sizes
and we've established how the scattered light will fluctuate over time.
Now let's move on to explain how we measure particle size using this information
Simply put,
snapshots of the light scattering signal are taken rapidly one after another
always comparing these back to the original signal measured.
between consecutive snapshots which are on the scale of Nano or microseconds the intensity signals are very similar.
Or well correlated.
But when we look at snapshots which are further apart in time
the similarity or correlation begins to decrease.
Eventually the intensity signal changes completely,
and there is no longer any correlation with the original signal this process is called autocorrelation
The larger the particles being measured the more slowly they diffuse and the longer it takes for
a complete loss of the correlation signal a small particles which undergo rapid diffusion
the correlation of the signal will decay rapidly.
So how do we use this information to calculate the particles hydrodynamic size?
The autocorrelation function we've created enables us to extract the translational diffusion coefficients.
Which I mentioned earlier.
These values are used in the Stokes Einstein equation to obtain our size information
variables such as solvent viscosity and temperature need to be known because they'll affect the particles diffusion rate.
Using DLS we can quickly measure the size of all the particles in a sample,
size distribution measured is shown in this graph as an intensity distribution.
This is the primary result and it shows the intensity of scattered light from each size population present in the sample.
These results can also be converted into a volume
or number size distribution if needed
DLS as used in Malvern Panalyticals Zetasizer range
can measure particle size distributions ranging from less than a nanometer up to several microns in size
it's a rapid and non-invasive technique which is extremely versatile and used in thousands of applications
For example: DLS is used to help characterize and optimize the pigments used in paints dyes and inks.
To advance research into drug delivery systems such as liposomes polymersomes,
to improve the formulation of emulsions and colloidal systems
to investigate and improve vaccine and drug formulations and many many more.
You can read about how people are using Zetasizer systems all over the world
for all sorts of applications in Malvern Panalyticals knowledge center.
this concludes our introduction to Dynamic Light Scattering
for further information about this versatile and powerful technique visit
www.malvernpanalytical.com/zetasizer