Dynamic light scattering (DLS) is the measurement of fluctuations in scattered light intensity with time. These fluctuations in intensity arise due to the random Brownian motion of nanoparticles. Therefore, the statistical behavior of these fluctuations in scattered intensity can be related to the diffusion of the particles. Since larger particles diffuse more slowly than small particles, one can readily relate particle size to measured fluctuations in light scattering intensity. With modern instruments, the technique is rapid and reliable.