Dynamic Light Scattering (DLS)

Dynamic Light Scattering (DLS), also called Quasi-Elastic Light Scattering (QELS), or Photon-Correlation Spectroscopy (PCS), is a widely used technique to measure the size of proteins, particles and other molecules in solution.

In Dynamic Light Scattering light intensity fluctuations taking place at microsecond or millisecond scales are measured. Those fluctuations are a measure of the diffusion constant (Brownian motion) of the molecules and are related to the hydrodynamic radius of a molecule.

Why Use Dynamic Light Scattering?

From the late 1980s commercial Dynamic Light Scattering (DLS) detectors started being used in commercial biophysical laboratories throughout the world. These instruments enabled size measurements of small volumes of proteins, biomaterials and particles in solution to be made, with small sample volumes and in relatively low concentration ranges. The ability to make these measurements in a relatively straightforward way, or in any case with complete recovery of the sample, soon made these instruments very popular. This is particularly true in protein studies where DLS instruments are used to screen proteins to predict if the protein is likely to crystallize before such a lengthy procedure was carried out. Other issues, such as stability, aggregation, complex formation and conformation in bio-molecular research are also studied using these instruments.

How does DLS work?

DLS works by measuring the intensity of light scattered by the molecules in the sample as a function of time. When light is scattered by a molecule or particle some of the incident light is scattered. If the molecule was stationary then the amount of light scattered would be a constant. However, since all molecules in solution diffuse with Brownian motion in relation to the detector there will be interference (constructive or destructive) which causes a change in light intensity. By measuring the time scale of light intensity fluctuations, DLS can provide information regarding the average size, size distribution, and polydispersity of molecules and particles in solution.

The faster the particles diffuse, the faster the intensity will change (if the light was bright enough this would be seen as a twinkling effect). The speed of these changes is thus directly related to the motion of the molecule. The diffusion of the molecules is essentially controlled by the following factors:

• Temperature – the higher the temperature the faster the molecules will move
• Viscosity of the Solvent – the more viscous the solvent the slower the molecules move
• The size of the molecules – the bigger the molecules, the slower they move

If the temperature and solvent are constant and known, the variation in the intensity of the scattered light is directly related to the “size” of the molecule. This number is referred to as the hydrodynamic radius (Rh). The hydrodynamic radius is the sphere defined by the molecule rotating in all directions plus the hydration layer, modified by how easy it is to pass the solvent through that volume. It is actually a measure of how easy it is to move the molecule through the solvent.
For more information about dynamic light scattering theory, please view our theory section.

 

DynaPro™ DLS detectors:

Wyatt Technology's DynaPro™ (Protein Solutions™) DLS instruments are the world's most widely used Dynamic Light Scattering technology:

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DynaPro™ DLS — Application Notes:

The great success of the DynaPro™ DLS systems is represented, in part, by the enormous number of peer-reviewed publications that cite them. There are more biopolymer-related publications using the DynaPro™ than all other DLS systems combined!

#	Description	Download
1	Determination of Critical Micelle Concentration (CMC)
2	Measurement of Mixed Micelle Size by Dynamic Light Scattering
3	Vesicle Size Distribution Analysis
4	Surfactants as Chaotropic Agents in Protein Systems
5	Conformation of Trimeric Form of Migration Inhibitory Factor
6	Insulin Quaternary Structure as a Function of PH
7	pH Dependent Monomer-Dimer Equilibrium Constants for GART
8	Monitoring Protein Thermal Stability-Glycosolated Hemoglobin Melting Point
9	Thermal Dissociation and Denaturation
10	Glycolytic Enzyme Enolase
11	Protein Purification Confirmation
12	Liposome Characterization by Dynamic Light Scattering
13	DNA and RNA Repair Enzymes
14	DynaPro Characterization of α-synuclein Oligomerization
15	Malate Dehydrogenase (MDH)
16	DynaPro Plate Reader for Buffer Optimization
17	Application of Dynamic Light Scattering in the Study of Dental Enamels
18	Protein Folding
19	Nuclear Pore Complexes
20	Recombinant Protein Structure
21	Real Time Monitoring of Macromolecular Complex Assembly and Disassembly
22	Polymersomes (Vesicles)
23	Monitoring Protein Complex Formation in Solution
24	Critical Micellization Temperature (CMT) of Block Copolymers of PEO and PPO