Answer :
Dynamic Light Scattering (DLS) is a physical methodology used for determining the size distribution of small particles in solution. It operates on the basis of Rayleigh scattering, with a laser light source scattering off particles, and the fluctuating intensities over time are analyzed to deduce particle size.
Dynamic Light Scattering (DLS), also known as photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QLS), is a technique widely used in physics, chemistry, and biochemistry for determining the size distribution of particles in solution or suspension.
The basis of DLS is Rayleigh scattering, where incident light (usually from a laser) is scattered by particles that are undergoing Brownian motion. According to Rayleigh scattering theory, for particles that are smaller than the wavelength of the incident light, the light is scattered in all directions, and the intensity of this scattered light varies with the size of the particles.
DLS measurements involve shining polarized laser light onto the sample and detecting the scattered light at different angles. The fluctuating intensities of the scattering are analyzed over time, and through a mathematical model, such as the Siegert relationship, information on the particle sizes can be extracted. This model calculates the decay rates from the intensity fluctuations, which can then be used to determine the diffusion constants and subsequently the hydrodynamic radius of the particles in solution.
An essential aspect of DLS is that it provides an intensity weighted distribution, meaning that larger particles have a more substantial effect on the measurement than smaller particles. This characteristic is crucial for accurately interpreting data from a DLS experiment. Instruments like the Zetasizer Nano combine laser sources, detectors, and computers to facilitate these measurements.
Overall, DLS is a critical method for analyzing the size distribution of particles and is especially effective for monodisperse spherical particles in suspension. It is often combined with other techniques, such as AFM and TEM, to achieve comprehensive size distribution data for analyzed samples.
