Time-varying flows for microfluidic particle separation

1. A method for spatially sorting particles using dielectrophoresis and field-flow fractionation comprising the steps:

providing a channel defining at least one electrode surface bordered laterally by a first sidewall and a second sidewall;

providing a first plurality of electrodes adjacent the electrode surface and extending along the electrode surface, and a second plurality of electrodes adjacent the electrode surface and extending along the electrode surface;

applying a first voltage to the first plurality of electrodes and a second voltage to the second plurality of electrodes such that the first plurality of electrodes is at a different electric potential than the second plurality of electrodes; and

moving a liquid at an oscillating flow rate through the channel, the liquid having a first plurality of particles suspended therein and a second plurality of particles suspended therein, wherein the first plurality of particles and the second plurality of particles each have a property that affects dielectrophoretic forces induced by the applied first and second voltages, wherein the property is different in the first plurality of particles than in the second plurality of particles such that the first plurality of particles are urged laterally away from the second plurality of particles and towards at least one of the first sidewall and the second sidewall to an extent sufficient to reduce a flow rate of the first plurality of particles compared to a flow rate of the second plurality of particles according to a liquid velocity profile across a cross-section of the channel;

thereby separating the first plurality of particles longitudinally from the second plurality of particles with field-flow fractionation resulting from the liquid lateral velocity profile.

2. The method of claim 1 , wherein the first plurality of electrodes and the second plurality of electrodes are concave-shaped and substantially symmetric about a center line of the channel.

3. The method of claim 2 , wherein the first plurality of electrodes and the second plurality of electrodes are selected from the group consisting of V-shaped electrodes, arcuate electrodes, and bowtie-shaped electrodes.

4. The method of claim 1 , wherein the first voltage and the second voltage are alternating voltages.

5. The method of claim 1 , wherein the first voltage is applied intermittently to the first plurality of electrodes.

6. The method of claim 5 , wherein the oscillating flow rate is synchronized with the intermittently applied first voltage.

7. The method of claim 6 , wherein the intermittently applied first voltage is an alternating current having a duty cycle, and wherein the oscillating flow rate is synchronized with the alternating current by synchronizing the duty cycle with oscillations in the flow rate.

8. The method of claim 1 , wherein the first plurality of particles and the second plurality of particles are independently selected from the group consisting of nucleic acids, cells, proteins, carbon nanotubes, and viruses.

9. The method of claim 8 , wherein the first plurality of particles comprises strands of DNA having a first length, and the second plurality of particles comprises strands of DNA having a second length that is different from the first length.

10. The method of claim 1 , further comprising a third plurality of electrodes disposed on a surface of the channel that is different than surfaces supporting the first and second pluralities of electrodes.

11. The method of claim 1 , wherein the first plurality of electrodes and the second plurality of electrodes are separated from the channel by a protective layer.

12. The method of claim 1 , wherein the first plurality of electrodes and the second plurality of electrodes are interdigitated.