Rotating Angle Dynamic Light Scattering
Score concentration, hydrodynamic size, polydispersity, particle count and detection of aggregates in one shot
Multiple angles makes it happen
Rotating angle dynamic light scattering (RADLS) is a powerful technique that builds on the fundamentals of classic single-angle DLS by rotating the DLS-module through multiple angles to get a unique set of data on every sample. This way, RADLS tells you hydrodynamic size of your sample independent of angle and reads out a particle concentration at the same time. RADLS combines light scattering data from multiple angles into one angle-independent Z-average hydrodynamic diameter. By capturing data from multiple angles, RADLS enables sizing analysis that can’t be fooled, catches even the tiniest bit of aggregation, and gives a read out on particle concentrations.
You and Mie
There are two key light scattering behaviors - isotropic Rayleigh scattering and anisotropic Mie scattering. The major difference between them lies in the size of the particles relative to the wavelength of light. Rayleigh scattering is for smaller particles and shows isotropic, angle-independent scattering. Mie scattering applies to larger particles and results in scattering patterns where the angle between the light source and the detector matters a lot. Taking anisotropic scattering into consideration is critical when characterizing larger viral vectors, lipid nanoparticles, aggregates, and other colloidal systems. If particles are large enough, the answers you get will vary based on where your instrument's detector is located.
Move it or lose it
RADLS is all about taking DLS reads from multiple angles on the same sample - so you don’t miss any particles just because they’re scattering light in a different direction. This technique is particularly valuable when studying larger-size samples, or samples with polydisperse particle size distributions, where Mie scattering causes dramatic variations in light scattering at different angles. RADLS collects data at multiple angles to deliver angle-independent data on size, polydispersity, shape, molecular weight, particle concentration and more.
With the ability to measure light scattering at lots of angles, then what’s the ‘best angle’ to determine size? Theoretically, you would need to measure at a scattering angle of 0° (θ=0°) to get the actual size, but this is impossible since it means the detector would need to look directly into the laser. Gathering data from many angles with RADLS makes it possible to combine all that info and extrapolate to θ=0° mathematically.
For large, heterogenous Mie scattering particles the detector will read a different Z-average hydrodynamic size at each angle. Reading Z-averages at multiple angles and extrapolating to θ=0° provides an angle-independent Z-average hydrodynamic diameter. For Rayleigh scatterers like proteins, the Z-average size will be independent of angle. However, for larger particles, like protein aggregates or LNPs, a strong relationship exists for Z-average size and angle.
RADLS + SLS counts for the win
Anisotropic scattering also has a major impact on static light scattering (SLS). If you want to measure particle concentration based on SLS you need to measure scattering intensity at multiple angles. Just like for DLS the ideal angle is 0°, but since this is not possible an extrapolation to θ=0° has to happen. Once you know how much light is being scattered, you have a key input to calculating how many nanoparticles are present in your sample.
Ready for more?
Scientists now have the right tool for protein, lipid nanoparticle and viral vector concentration and sizing studies with an instrument that combines rotating angle dynamic light scattering (RADLS), multi-angle light scattering (MALS) and UV/Vis. Have a question or ready to find out more?