Bidirectional field-flow particle separation method in a dielectrophoretic chip with 3D electrodes

This paper proposes a bidirectional field-flow separation method in a dielectrophoretic chip with 3D electrodes. The DEP chip presents a sandwich structure glass/silicon/glass. The top glass layer assures two inlets and two outlets, disposed in cross, for the inlet/outlet of particle suspension and buffer solution, respectively. The silicon layer defines the walls of the microfluidic channels and at the same time the electrodes (rows of pillars with square cross-section) of the DEP device. The bottom glass presents via holes (one for each pillar) and a metallization layer which assures both the connections between pillars (a row of pillar being connected at one electrode) and also the connection of the electrodes with the PCB. The 3D electrodes structure that is used in this device is not only used for generating an uniform DEP force across the microfluidic channel but also for achieving a gradient of the velocity (and in this way a variable hydrodynamic force) in the microfluidic device. DEP and hydrodynamic forces are used in the separation technique of two particle populations. The method consists of four steps. First, the solution with the mixture of two particle population is inserted in the microfluidic chamber between the silicon pillars. Second, by applying an electric field the two populations are separated in different locations according to their electrical properties. In the third step one population is first collected at one outlet by flowing a fresh buffer solution. Finally, the second population is collected at the second outlet by flowing fresh buffer in the perpendicular direction. The device has been tested successfully with live/dead yeast cells.