Evaluation of a dielectrophoretic bacterial counting technique

Dielectrophoresis, an electrokinetic migration of particles, can occur in non-uniform alternating electric fields and is dependent upon the dielectric nature of the cells and their suspending medium. An enumeration system utilising this phenomenon is described, which has the potential to count particles selectively, including different bacterial or eukaryotic cell species and even sub-populations of different cell viability states or sizes. Relationships were observed between suspension concentrations and the extent of dielectrophoretic (DEP) collection for polystyrene latex beads, pure bacterial samples and mixtures of bacterial species including Escherichia coli, Serratia marcescens, Pseudomonas aeruginosa and Bacillus subtilis. A similar relationship was utilised for polystyrene latex as a calibration line to enable the concentration of particles in a suspension to be determined according to the level of DEP collection. The particle concentration of an unknown test sample was found to lie within the predicted concentration range determined on the basis of DEP collection. In addition, the predicted limits were found only to deviate between -6.2 and +6.9% from the mean particle concentration.