Separation of live and dead microorganisms in a micro-fluidic device by dielectrophoresis

The dielectrophoretic separation of micro-organisms, based on cellular membrane damage, was carried out using a microfabricated fluidic device. The fluidic device was composed of an indium-tin oxide electrode with castellated electrode patterns, an acrylic board with inlet and outlet holes for micro-organisms suspension, and a silicone separator with a fluidic channel (width, 2 mm ; length, 35 mm) between the electrode substrate and acrylic board. Dielectrophoretic separation was demonstrated for a mixture of live and heat-treated Escherichia coli bacteria labeled by fluorescent stains. The mixture was injected into the fluidic device at a flow rate of 440 μm/sec. Both live and dead bacteria were collected around castellated electrode when an alternative (sinusoidal) electric field (frequency 100 kHz, voltage 20 Vpeak-to-peak) was applied to the castellated electrode. The dielectrophoretic separation was found by changing the electric field frequency from 100 kHz to 7 MHz. Only the heat-treated E. coli cells were flown out from the fluidic device, while the live E. coli cells remained being captured between the electrodes. The results demonstrated that the fluidic device equipped with a microelectrode array provides a convenient way for the dielectrophoretic concentration and separation of targeted bio-particles in biomedical applications.