Homodyne electrophoretic light scattering of polystyrene spheres by laser cross-beam intensity correlation

Homodyne light fluctuation spectroscopy is combined with an electrophoresis apparatus to provide a technique that rapidly measures electrophoretic mobilities of charged particles suspended in a liquid medium. Two parallel laser beams, polarized in the same direction, are focused into a scattering cell by a cylindrical lens. The laser beams interfere at the focal point of the lens to produce a fringe intensity profile. As scattering particles are driven through the fringes, the scattered light intensity is modulated. This modulation is detected by digital autocorrelation of photoelectron pulses from a photomultiplier. With this technique the electrophoretic mobility of 1-micro diam monodisperse polystyrene spheres was determined to be 4.6 +/- 0.2 (micro/sec)/(V/cm) in water.