Optical technique for measuring the positive and negative dielectrophoretic behaviour of cells and colloidal suspensions

A dual beam optical spectrometer has been developed for the rapid measurement of the dielectrophoretic behaviour of cells and other colloidal particles subjected to nonuniform AC electrical fields. A significant improvement over previous designs is the ability to characterise both positive and negative dielectrophoresis, which in turn provides a simple method for deriving the practical conditions required for the selective manipulation and separation of cells using dielectrophoretic forces. Measurements are reported for viable and nonviable yeast cells, as a function of the conductivity of their suspending medium and also of the magnitude and frequency of the applied AC voltage