Dynamic Light Scattering
Dynamic light scattering for proteins and other biologics
Equipping biologics researchers with dynamic light scattering instruments designed for biologics
How does dynamic light scattering work?
Shine a laser on a solution of particles and you’ll get plenty of light scattering back out at you. When the laser wavelength is much larger than the particles, you get equal amounts of light scattering in every direction – that’s why we use a 660 nm laser in our DLS systems.
DLS can tell you a lot about the size of the particles in solution by measuring how rapidly that scattered light changes over time (Figure 1). Since small particles zip around quickly, the intensity of light changes quickly. Vice versa for larger ones because they are slower to move around. Analyzing whether light intensity is changing fast or slow – that’s the secret sauce of DLS.
Here’s how to think about analyzing light scattering data for DLS: pick a point in time – now jump forward a microsecond. Odds are good most particles haven’t moved around yet – so the light scattering hasn’t changed and the data from time zero and a microsecond later are about the same. In other words, they have a high correlation.
Now instead of a microsecond, jump forward a full second. Most particles will be in totally different spots – and you now have zero correlation in the data between your starting point and your jump one second later. Graph these correlation values for a range of jumps of different durations and you get a Correlation Function (Figure 2). How quickly particles go from high correlation to zero correlation tells you their average size. This is also why DLS is sometimes called photon correlation spectroscopy (PCS).
To get from a Correlation Function to the stuff you really care about – data – two analysis methods are used. The first method applies a ‘best fit’ to the Correlation Function and the shape of that fit leads to a diffusion coefficient, an average size, and a size distribution. To get from diffusion coefficient to particle diameter the Stokes-Einstein equation comes in handy:
Figure 1. Light scattering intensity changes differently over time for different sized particles.
Figure 2. Correlation functions for proteins of two different sizes.
In the world of biologics, DLS will not only tell you the size of your sample, it is also a quick check to determine if your sample is aggregated. Since large particles scatter light intensely, DLS can detect even very rare aggregates in a sample. Sending up a warning flag on protein aggregates can save you from relying on data from a sample already past its prime, or explaining why your antibody is no longer performing at its peak.
All Unchained Labs dynamic light scattering instruments deliver:
- Accurate, repeatable, and reproducible sizing data in less than a minute per sample
- Data using the optimal combination of small sample volumes and low concentrations
- Average diameter results for whole samples
- Size distributions when multiple peaks are found
- Highly sensitive detection of aggregates, even ones too large or too rare for traditional SEC analysis
- Size measurements from 0.3 – 1000 nm
- Measurements down to 0.1 mg/mL for lysozyme, or lower concentrations for larger proteins
Check out our dynamic light scattering instrument line-up below, with 2 solutions designed to solve biologics problems.
Ready for more?
Biologics researchers can now find the right tool built for biologics problems across two dynamic light scattering instruments. Have a question or can’t wait to find out more?