Dynamic Light Scattering

Dynamic Laser Light Scattering, also called Photon Correlation Spectroscopy (PCS) or Quasi Elastic Laser Light Scattering (QELS) is a technique for the determination of Hydrodynamic Radius of macromolecules and particulates in solution. In Dynamic Light Scattering the fluctuation of the scattered light, caused by the Brownian Motion of the molecules, is detected by a photon counting detector. Therefore a laser beam is focused in the sample causing the particles in the scattering volume to scatter light in all directions. In Dynamic Laser Light Scattering these scattered photons are counted. Small particles diffuse “faster” and show a higher scattering frequency than larger particles which diffuse “slower”, showing a lower scattering frequency.
 
The collected data is used to establish an autocorrelation function from which the Diffusion Coefficient directly can be derived. Using the Stokes-Einstein equation, the Hydrodynamic Radius and the size distribution can be calculated.

D = (k_{B *}T) / (6πη _* R_h)

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