Dynamic light scattering (DLS) is a technique that is used to measure the size of particles, generally particles that are in the sub-micron region. The technique is also referred to as photon correlation spectroscopy and quasi-elastic light scattering.
The technique can be used to determine the size of liposomes, spherical bilayer vesicles that may be naturally derived or synthesized from man-made substances. Liposomes are mainly used in the biopharmaceutical industry as carriers for drug delivery in cancer treatment.
Liposome size and the amount of drug that can be loaded into liposomes is key in terms of the drugs’ pharmacodynamic and pharmacokinetic parameters. DLS can help to provide accurate information about the size of liposomes, which is critical to ensuring that drug delivery systems are effective. The size of liposomes varies, but is typically around 100nm.
Particles suspended in a liquid medium undergo Brownian motion, which is slower, the larger the particle is. The solvent molecules have more impact on the movement of smaller p articles, which therefore move more rapidly. In DLS, light scattering by the particles is used to monitor Brownian motion.
The light scattering that occurs when a light is shone onto particles in solution can provide useful information about the size, weight, surface structure, charge, stability and concentration of the particles. Analysis over time can also provide information about changes in the solution. Researchers can learn about the interactions between particles in the fluid, as well as other aspects such as thermal melting points.
Dynamic light scattering technique
The speed that particles diffuse at as a result of Brownian motion is calculated by measuring the rate of fluctuation in the intensity of the scattered light. The intensity fluctuates more rapidly with small particles than it does with large particles.
The fluctuation is measured by comparing the signal intensity at one time with signal intensity a very short time later. With larger particles, it takes a long time for the correlation of the signal to decay, whereas the more rapid movement of smaller particles means the correlation of the signal decreases more quickly.
This change indicates the size of the particle and provides what is referred to as the hydrodynamic diameter, since the value refers to how the particle diffuses in solution.
Reviewed by Sally Robertson, BSc
Effect of fluorescent staining on size measurements of polymeric nanoparticles using DLS and SAXS: http://pubs.rsc.org/EN/content/articlelanding/2015/ay/c5ay02005k#!divAbstract