FIELD OF INVENTION

The present invention relates to an apparatus for sorting particles by dielectrophoresis in a microfluidic system.

BACKGROUND OF THE INVENTION

Dielectrophoresis (DEP) refers to a force exerted on particles of interest when it is subjected to a non-uniform electric field. The direction and magnitude of the force depend on the particle size, the electrical properties of the particles and medium, and the magnitude, frequency, and waveform of the imposed electric field. Thus, DEP provides a non-invasive method for sorting particles and cells in a microfluidic system. An example of an apparatus using DEP for sorting particles is provided in US

Patent Publication No. 2006/0177815 which discloses methods, devices and systems that utilize dielectrophoretic forces to separate a target species from a plurality of species in a sample. Another example of such apparatus is provided in US Patent Publication No.

2007/0131554 which discloses a microfluidic dielectrophoresis separating device. The microfluidic dielectrophoresis separating device includes a primary passage, at least a secondary passage and at least an electrode assembly. The primary passage has a primary flow containing a plurality of particulates flowing therein. The secondary passage has an input path and an output path and is connected with the primary passage. The electrode assembly generates a dielectrophoresis force to drive a specific one of the particulates into the output path.

However, such apparatus are posed with problems such as low sorting efficiency, difficulty in changing trajectory of the particles in the microfluidic system and low surface area of electrodes that can be utilised to generate the electric field.

Therefore, there is a need to provide a dielectrophoresis apparatus that addresses the aforementioned problems. SUMMARY OF INVENTION

The present invention provides an apparatus for sorting particles by dielectrophoresis. The apparatus comprises of a primary microchannel (110), at least one side microchannel (120), and at least three electrically coupled electrodes (131 , 132, 133). The electrodes (131 , 132, 133) are arranged in the primary microchannel (110) and are positioned near the proximal end of the side microchannel (120), wherein a first electrode (131) is a planar electrode forming a part of the bottom inner surface of the primary microchannel (110), and wherein a second electrode (132) is a planar electrode forming a part of the top inner surface of the primary microchannel (110), and wherein a third electrode (133) is a comb-like electrode suspended in the middle of the primary microchannel (110) and planarly inclined towards the side microchannel (120).

Preferably, the electrodes (131 , 132, 133) are placed vertically opposite one another, wherein the first electrode (131) is placed directly below the third electrode (133) while the second electrode (132) is placed directly above the third electrode (133).

Preferably, the electrodes (131, 132, 133) are connected to one or more power source of either DC or AC voltage, and wherein the first and second electrodes (131, 132) have an opposite polarity from the third electrode (133).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 illustrates a top view of an apparatus for sorting particles by dieletrophoresis according to an embodiment of the present invention.

FIG. 2 illustrates a cross sectional view of the apparatus of FIG. 1.

FIGS. 3(a-d) illustrate an operation of the apparatus of FIG. 1 according to an embodiment of the present invention. DESCRIPTION OF THE PREFFERED EMBODIMENT

A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail.

Referring to FIGS. 1 and 2, there is provided an apparatus for sorting particles by dielectrophoresis. The apparatus generally comprises of a primary microchannel (110) having a side microchannel (120) and three electrically coupled electrodes (131, 132, 133). The apparatus may comprise additionally one or more side microchannels (120) that are capable of flowing fluid and sorted particles from the primary microchannel (110) to a side outlet (121).

The primary microchannel (110) is used to flow fluid containing particles from its inlet (111) to its outlet (112), while the side microchannel (120) is used to flow particles sorted from the fluid flowing through the primary microchannel (110) to a side outlet (121). The primary channel (110) is suitably made of silicon, glass or polymers such as, but not limited to polydimethylsiloxane (PDMS), poly-methyl- metha-crylate (PMMA) or polyimide.

The three electrodes (131, 132, 133) are arranged in the primary microchannel (110) and are positioned near the proximal end of the side microchannel (120) so as to deflect selected particles from the fluid into the side channel (120) and onto distal end of the side microchannel (120). A first electrode (131) is a planar electrode forming a part of the bottom inner surface of the primary microchannel (110). A second electrode (132) is a planar electrode forming a part of the top inner surface of the primary microchannel (110). A third electrode (133) is a comb-like electrode suspended in the middle of the primary microchannel (110). Moreover, the third electrode (133) is planarly inclined towards the side microchannel (120). The electrodes (131 , 132, 133) are placed vertically opposite one another, wherein the first electrode (131) is placed directly below the third electrode (133) while the second electrode (132) is placed directly above the third electrode (133). Preferably, the electrodes (131, 132, 133) are made out of conducting materials such as, but not limited to doped polysilicon, metals or conductive polymers. Moreover, the electrodes (131, 132, 133) are connected to one or more power source of either DC or AC voltage. At any given time, the first and second electrodes (131 , 132) have an opposite polarity from the third electrode (133). Thus, an electric field is generated in between the first and third electrodes (131 , 133) and another electric field is generated in between the second and third electrodes (132, 133) when voltage is applied to the electrodes (131 , 132, 133).

Through appropriate arrangement of the electrodes (131 , 132, 133) and controlling of the voltages applied to the electrodes (131, 132, 133), particles having a particular properties or sizes can be sort out from a fluid flowing through the primary microchannel (110).

Referring now to FIGS. 3, a method of sorting particles by using the apparatus of FIG. 1 is illustrated. Initially, a fluid is flowed through the primary microchannel (110) as shown in FIG. 3a. Voltage is applied to the electrodes, wherein the first and second electrodes (131, 132) are applied with electrical potential having polarity opposite of those from the third electrode (133). Hence, an electric field is generated in between the first and third electrodes (131, 133) and in between the second and third electrodes (132, 133).

As the fluid approaches the electrodes (131 , 132, 133), the particles (10) of the fluid are subjected to a non-uniform electric field that creates a DEP force onto selected particles (10a) of the fluid. The DEP force levitates and attracts the selected particles (10a) towards the third electrodes (133) as shown in FIG. 3b. Hence, the DEP force blocks the progress of the selected particles (10a) through the primary microchannel (110) while allowing non-selected particles (10b) to pass through to the outlet (112) of the primary microchannel (110). At the same time, the hydraulic force from the fluid flow continues to push the particles (10) forward and thus, a combination of the DEP force and the hydraulic force generate a net force in the direction along the third electrode (133) as shown in FIG. 3c. As a result, the selected particles (10a) are deflected into the side microchannel (120) and on to the outlet (121) of the side microchannel (120) as shown in FIG. 3d. Hence, particles of a particular size or properties can be sort out from the fluid. If the hydraulic force is greater than the DEP force, the selected particles (10a) may flow through the outlet (112) of the primary microchannel (110). However, the comb-like structure of the third electrode (133) creates a multiple electric field with the first and second electrodes (131 , 132) and thereby, the selected particles (10a) that escaped from the initial DEP force is subsequently exposed to another electric field. Thereon, the sorted particles (10a) can be deflected towards the side microchannel (120).

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrated and describe all possible forms of the invention. Rather, the words used in the specifications are words of description rather than limitation and various changes may be made without departing from the scope of the invention.