A primer on particle sizing using dynamic light scattering

The efficacy and subsequent success of a pharmaceutical is strongly dependent on its shelf life and its stability under targeted solution conditions. A typical manifestation of formulation instability is an increase in particle size, due to aggregation of the analyte or carrier. As the particle size increases, efficacy is diminished, primarily due to the decrease in the active surface area. Because of the correlation between efficacy and size, particle sizing is quickly becoming a routine step in the development of more stable and effective formulations. Dynamic light scattering (DLS), also known as photon correlation spectroscopy (PCS) and quasi-elastic light scattering (QELS), provides many advantages as a particle size analysis method. DLS is a noninvasive technique that measures a large population of particles in a very short time period, with no manipulation of the surrounding medium. Modern DLS instruments, notably the Zetasizer Nano system (Malvern Instruments, Southborough,