ERLS
Electrorotational Light Scattering (ERLS)
Dynamic light scattering (DLS) analyzes the fluctuations of light scattered by suspended particles. When an autocorrelation analysis of the light intensity fluctuations is performed, the stochastic nature of the particle motion generally results in a decorrelation of the obtained autocorrelation function (ACF). For example, pure translational diffusion within a monodisperse suspension results in a single exponentially decaying ACF. ERLS combines electrorotation (ER) with dynamic light scattering.
The method detects ER from a particle ensemble in a special optical ER-chamber. A homodyne setup is used. First measurements were carried out with an ER-chamber fitted into the cuvette holder of a commercial light scattering device (Coulter N4 particle sizer)[1]. In order to optimize the ER detection with ERLS we also used a setup with all components being freely accessible [44]. We tested ERLS with human red blood cells. The induced cell rotation led to a faster decorrelation of the ACF. A simple optical particle model was developed that describes the influence of ER on the initial part of the ACF [35]. Basing on this model we developed different criteria to extract the rotation speed from the initial ACF-decay. The figure shows an example of an ERLS frequency spectrum obtained from a red cell suspension. The solid line is the comparison to the theoretical ERLS-spectrum calculated for the simple optical cell model and from the dielectric cell model [39]. Although the absolute rotation speed and the rotation sense are not yet directly accessible, ERLS offers computerized, statistically significant measurements of dielectric particle properties which are especially suitable for non-biological applications, e. g. the study of colloidal particles.
More information: Jan Gimsa