Dynamic Light Scattering (DLS - also known as Photon Correlation Spectroscopy or Quasi-Elastic Light Scattering) is one of the most popular light scattering techniques that can be used to determine the size distribution profile of small particles in suspensions, emulsions, micelles, polymers, proteins, nanoparticles or colloids.

Small particles in suspension undergo random thermal motion known as Brownian motion.  This random motion is modeled by the Stokes-Einstein equation, according to which the diffusion coefficient (D) is inversely proportional to the particle size (d).

In this technique, the suspension is illuminated by a laser beam and the fluctuations of the scattered light from particle is random motion are detected, at a known scattering angle θ, by a fast photon detector. Hydrodynamic diameter of the suspended particles is obtained by calculating the auto correlation functions of the time dependent intensity fluctuations. Multi-angle instruments can determine the full particle size distribution. And the same technique can provide zeta potential (surface charge) of the particles using the electrophoretic light scattering and laser doppler method.

Our research group have access to Beckman Coulter Delsa Nano Submicron Particle analyzer that has the capability to measure full particle size distribution and zeta potential with the use of various sample holders; disposable size/zeta cell, flow cell, high concentration cell, flat surface cell and low conductivity cell, depending on the exact information required.

Laser source

Lens

Lens

Photon detector

Sample