Dynamic Light Scattering (DLS)

Size Characterisation of Proteins, Polymers and Colloidal Dispersions

Dynamic light scattering (DLS), sometimes referred to as Photon Correlation Spectroscopy (PCS) or Quasi-Elastic Light Scattering (QELS), is a non-invasive, well-established technique for measuring the size of molecules and particles typically in the submicron region, and with the latest technology lower than 1 nanometre.

Applications

Typical applications are the measurement of the size and size distribution of particles emulsions and molecules dispersed or dissolved in a liquid.
e.g.: Proteins, polymers, micelles, carbohydrates, nanoparticles, colloidal dispersions, emulsions, microemulsions.

Principle of Measurement

Particles, emulsions and molecules in suspension undergo Brownian motion. This is the motion induced by the bombardment by solvent molecules that themselves are moving due to their thermal energy.

If the particles or molecules are illuminated with a laser, the intensity of the scattered light fluctuates at a rate that is dependent upon the size of the particles as smaller particles are “kicked” further by the solvent molecules and move more rapidly. Analysis of these intensity fluctuations yields the velocity of the Brownian motion and hence the particle size using the Stokes-Einstein relationship.

What is actually measured?

The diameter that is measured in Dynamic Light Scattering is called the hydrodynamic diameter and refers to how a particle diffuses within a fluid. The diameter obtained by this technique is that of a sphere that has the same translational diffusion coefficient as the particle being measured.

The translational diffusion coefficient will depend not only on the size of the particle “core”, but also on any surface structure, as well as the concentration and type of ions in the medium. This means that the size can be larger than measured by electron microscopy, for example, where the particle is removed from its native environment.

Advantages of Malvern Dynamic Light Scattering technology

• Accurate, reliable and repeatable particle size analysis in one or two minutes
• Measurement in the native environment of the material
• Mean size only requires knowledge of the viscosity of the liquid
• Simple or no sample preparation, high concentration, turbid samples can be measured directly
• Simple set up and fully automated measurement
• Size measurement of sizes < 1nm
• Size measurement of molecules with MW < 1000Da
• Low volume requirement (as little as 12µL)
• Compliance with regulatory standards ISO 13321, 21 CFR Part 11

More Information :

	Instrumentation for classical 90 degree Dynamic Light Scattering measurements
	New dynamic light scattering technology for high sensitivity and measurement at high concentration (NIBS)
	Zetasizer home page
	On demand presentation: What is Dynamic Light Scattering (DLS)? This presentation gives a brief introduction into how Dynamic Light Scattering works for the sizing of molecules, particles, and emulsions. (no registration required for this 4 minute presentation).