Dielectrophoretic separation of bacteria using a conductivity gradient.

Dielectrophoresis, the lateral motion induced on particles by non-uniform electric fields, is a sensitive function of the electrical conductivity of the particle suspending medium. This dependence is exploited in a new technique for separating bioparticles from suspended mixtures. The bioparticles are first immobilised by positive dielectrophoresis at electrodes in a separation chamber, and the conductivity of the liquid flowing through the chamber is then gradually and continuously increased so as to produce a conductivity gradient with time. The bioparticles are released from the electrodes according to their own dielectric properties and as a function of flow rate and medium conductivity. This is demonstrated for pure suspensions and mixtures of the bacteria Bacillus subtilis, Escherichia coli and Micrococcus luteus.