On the electrophoretic mobility of biological cells.

A theoretical study has been performed on the electrophoretic mobility of a large colloidal particle with a surface charge layer as a model for biological cells. An approximate mobility expression is derived which is applicable to the general case of an arbitrary distribution of membrane-fixed charges. This expression consists of two terms: the first is a weighted average of potentials over the surface charge layer, while the second is that of the volume density of membrane-fixed charges and does not depend on the electrolyte concentration. At high electrolyte concentrations (corresponding to physiological conditions), where the potentials are very low owing to the shielding effects of electrolytes, the first term diminishes so that the mobility is determined mainly by the second term. This means that a particle with zero surface potential can exhibit a non-zero mobility, in contrast to the prediction from the classical Smoluchowski theory. Comparison is also made with the theory of Hermans and Fujita for the electrophoresis of polyelectrolytes.