1. Dynamic Light Scattering

3. Introduction In 1869 J.Tyndall performed the first experimental studies on light scattering from aerosols. He explained the blue colour of the sky by the presence of dust in the atmosphere. DLS is routinely used for fast (a few minutes) and accurate (1-2%) measurements of translational diffusion coefficients of macromolecules in solution and rotational diffusion coefficients of small globular proteins and oligonucleotides, and for anemometric measurement of linear and turbulent flow. DLS is the most powerful technique for accurate measurements of translational diffusion coefficients of macromolecules in solution. Dynamic Light Scattering is a generic term encompassing all of the light scattering methods that provide information on molecular dynamics. DLS(Dynamic Light Scattering) analyses are routinely used in biology laboratories to detect aggregates in macromolecular solutions, to determine the size of proteins,nucleic acids, and complexes or to monitor the binding of ligands. For samples composed of a single population of particles, two characteristics derived from Dt(Diffusivity). First the mean hydrodynamic particles size can be calculated assuming a simple geometry like that of a sphere. Second, the polydispersity of the population is given by the standard deviation on Dt. The degree of poly disparity of this solution is essentially due to asymmetry in shape and to inter molecular interaction. In a mono disperse sample all particles are identical in size and shape.

4. The Brownian motion is that small molecules moves faster than large ones. This movement of for example the molecules in liquid, causes constant collisions with other molecules. Due to these frequent collisions is the movement of the liquid molecules completely at random and no orderly structure exists. How intensive, respectively fast, this trembling motion on a molecular level really is, depends on the temperature and viscosity of the liquid. Here high temperatures mean a faster motion. If the liquid contains a particle, so it also constantly collides with liquid molecules, causing a trembling motion of the particles. The speed of this trembling motion of the particle though depends besides on the viscosity and temperature of the surrounding liquid also on the particle size. The Brownian motion is that small molecules moves faster than large ones. This movement of for example the molecules in liquid, causes constant collisions with other molecules. Due to these frequent collisions is the movement of the liquid molecules completely at random and no orderly structure exists. How intensive, respectively fast, this trembling motion on a molecular level really is, depends on the temperature and viscosity of the liquid. Here high temperatures mean a faster motion. If the liquid contains a particle, so it also constantly collides with liquid molecules, causing a trembling motion of the particles. The speed of this trembling motion of the particle though depends besides on the viscosity and temperature of the surrounding liquid also on the particle size. The Brownian motion is that small molecules moves faster than large ones. This movement of for example the molecules in liquid, causes constant collisions with other molecules. Due to these frequent collisions is the movement of the liquid molecules completely at random and no orderly structure exists. How intensive, respectively fast, this trembling motion on a molecular level really is, depends on the temperature and viscosity of the liquid. Here high temperatures mean a faster motion. If the liquid contains a particle, so it also constantly collides with liquid molecules, causing a trembling motion of the particles. The speed of this trembling motion of the particle though depends besides on the viscosity and temperature of the surrounding liquid also on the particle size.