US20030170131A1

US20030170131A1 - Microfluidic device including a micropump

Info

Publication number: US20030170131A1
Application number: US10/096,179
Authority: US
Inventors: Richard Zare; Garth Simpson; Clyde Wilson
Original assignee: Leland Stanford Junior University
Current assignee: Leland Stanford Junior University
Priority date: 2002-03-08
Filing date: 2002-03-08
Publication date: 2003-09-11

Abstract

Microfluidic devices are disclosed. The microfluidic devices comprise pumps and mixers in which a microrotor rotated by coupled dipoles induced by alternating electric fields moves fluids in which it is immersed.

Description

GOVERNMENT SUPPORT

[0001] This invention was made with Government support under Grant No. DA09873-06 awarded by the National Institutes of Health. The Government has certain rights to this invention.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to microfluidic devices using electrically driven dielectric microrotors/impellers for pumping and mixing fluids in microchannels.

BACKGROUND OF THE INVENTION

The fabrication and use of microchannels in the manipulation of small fluid volumes in chemical and biochemical analysis is well known. Small fluid volumes have been moved through microchannels employing electro-kinetic flow. Mechanical pumping systems have also been used to move and direct fluids within microchannels. These systems employ microscale devices utilizing external and internal microfabricated pumps and valves. The microfabrication methods are costly because they require bulky and expensive equipment. There is a need for a microfluidic device which can pump and mix fluids in microchannels for chemical and biochemical analysis and synthesis.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a microfluidic device having at least one microchannel in which the fluid in the microchannel is pumped and/or mixed by electrically driven dielectric micro-rotor/impellers.

It is another object of the present invention to provide a microfluidic device employing microchannels in which a micro rotor is employed to pump fluid along the channels.

It is a further object of the present invention to provide a microfluidic device in which a dielectric rotor/impeller mixes fluid in the vicinity of the rotor/impeller.

A microfluidic device having at least one microchannel is provided. A microrotor/impeller is disposed in said microchannel and driven by dipole field induced coupled electrorotation to pump and/or mix the fluid in said channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects of the invention will be more clearly understood from the following description when read in conjunction with the accompanying drawings in which: [0008]
FIG. 1 is a top plan view of a capillary channel formed in a substrate with a microfluidic pump employing a microrotor/impeller. [0009]
FIG. 2 is a sectional view of the capillary channel and microfluidic pump taken along line [0010] 2-2 of FIG. 1 with a cover not shown in FIG. 1.
FIG. 3 is a sectional view of the capillary channel microfluidic pump taken along the line [0011] 3-3 of FIG. 1 with a cover not shown in FIG. 1.
FIG. 4 is an enlarged view of the region microrotor/impeller of FIG. 1. [0012]
FIG. 5 shows another embodiment of a capillary channel formed in a substrate with a microfluidic pump. [0013]
FIG. 6 is a top plan view of a capillary channel and microfluidic pump having a constant channel dimension. [0014]
FIG. 7 is a top plan view of another capillary channel with another microfluidic pump. [0015]
FIG. 8 is a top plan view of microfluidic device with a micropump at the fluid supply reservoir. [0016]
FIG. 9 is a top plan view of a microrotor/impeller disposed in a well for mixing fluids. [0017]
FIG. 10 is a schematic illustration of microfluidic device incorporating micropumps in accordance with the present invention.[0018]

DESCRIPTION OF PREFERRED EMBODIMENT

Microfluidic device of the present invention includes at least one microchannel of capillary dimensions with a micropump comprising a microrotor/impeller rotated by dipole field induced coupled electrorotation for pumping and/or mixing fluid in the microchannel. The device may include a number of microchannels for transferring fluid to intersections where chemical reactions or chemical or biological reactions can be carried out using microquantities of reagents or samples. By way of example the microchannels may have cross sectional dimensions in the range of 1 micron to 500 microns and the rotor/impellers have diameters from 0.5 microns to perhaps 50 microns or more. [0019]
Referring to FIGS. [0020] 1-4, a microchannel 11 is formed in a substrate 12. The substrate can be any material which does not react with the fluid which is being pumped. The substrate can, for example, be an insulator a semiconductor material. The microchannel can be formed by photolithography and etching which is well known in the semiconductor art. Alternately the substrate may be plastic and the microchannel may be formed in the plastic material by injection molding, stamp molding and embossing. Referring to FIG. 1, the channel 11 is formed with a bulge or protruding wall portion 13. The substrate is provided with a cover plate 15, FIG. 2, to form a capillary passage. A dielectric microrotor/impeller 14 is located adjacent to bulge. The rotor/impeller is selected to have a different polarizability than the fluid in the microchannel 11. In one embodiment the rotor/impeller comprises microspheres obtainable from Molecular Probes (Eugene, Oreg.), Polysciences, Inc. (Warrington, Pa.) or Bangs Laboratories, Inc. (Fishers, Ind.). The bulge 13 and rotor 14 are in close proximity so that they are electrostatically coupled to one another. Spaced electrodes 16 and 17 may be formed on the upper surface of the substrate. In the examples shown in FIGS. 1-4 the electrodes 16 and 17 are embedded in the piece so that they lie substantially opposite the spherical rotor to provide substantially uniform linear electric fields through the microrotor/impeller 14 and the bulge 13. However, it is apparent that, in view of the fact that the microchannels are involved, the electrodes can be formed on the surface of the substrate.
Application of alternating electric voltage to the electrodes generates linear [0021] electric fields 18, FIG. 4. These electric fields induce dipoles 21 and 22 in the dielectric rotor 14 and substrate bulge 13, respectively. With the rotor offset from the bulge, the dipole fields attract and the rotor rotates in the direction shown by the arrow 24. When the fields alternate there are still attracting forces which cause the rotor to continue to rotate at a rotational velocity which is dependent upon the alternating frequency of the electric fields, the viscosity and polarizability of the fluid and the dielectric properties of the rotor. In order for rotation to occur the fluid and the rotor and bulge need to be polarizeable. The direction of rotation depends on the relative positions of the rotor and bulge within the electric field.
As seen in FIG. 4, rotation of the rotor viscously drags the fluid to pump the fluid in the direction of the arrows [0022] 26 and along the channel 11. Additionally as the rotor rotates it will mix fluid in the vicinity of the rotor. The rotor is maintained adjacent the bulge by mechanical restriction or an optical trap. Thus, there has been provided a simple pump which operates by dipole field induced coupled electrorotation for causing fluid to flow along microchannels or microcapillaries.
Referring to FIG. 5, [0023] electrodes 31 and 32 are placed at the bottom of the channel 11 and provide longitudinal alternating electric fields which induce the dipoles 33 in the bulge and 34 in the rotor which cause the rotor to rotate in a counter-clockwise direction as indicated by arrow 36 and pumps fluid as indicated by the arrow 37.
By way of example, the alternating frequency of the electric field can be in range of 400 kHz to 700 kHz and the voltage between 1.5 and 3.5 peak-to-peak. In one example, this caused rotation of the microrotor at 800 to 1800 rpm for a microsphere having 0.75 μm diameter. It is apparent that the rotor/impeller can take other shapes such as a disc-shaped rotor, hexagonal-shaped, octagonal, etc. to provide more efficient pumping. [0024]
In certain applications, it is desirable to have a channel of uniform dimensions. FIG. 6 shows a [0025] channel 40 having a zig-zag shape with the microrotors/impellers 41, 42 located at one edge of the protruding walls 43, 44. The electrodes 46, 47 are on opposite sides of the rotors 41, 42. The rotors pump by dipole field induced coupled rotation as indicated by the arrows 49.
In another embodiment, FIG. 7, two [0026] microrotors 51, 52 are held next to each other in electric fields generated by the electrodes 53 and 54 by an optical trap, not shown. Induced dipoles 56, 57 cause the rotors to rotate in opposite directions and pump fluid along the channel in the direction of rotation of the microrotor closest to a wall (in the illustrated example, in the direction of arrow 58).
The [0027] end 61 of a microchannel 62 is shown in FIG. 8 cooperating with a fluid reservoir 63. A pump formed by the microrotor/impeller 64, bulge 66 and electrodes 67, 68 rotate the impeller and pump fluid from the reservoir into the microchannel.
In many applications, it is necessary to mix fluids in wells. The present invention provides an excellent mixing device for use in microwells. Referring to FIG. 9, a [0028] microwell 71 is shown formed in a substrate 72. A microrotor/impeller 73 is disposed in the well and held adjacent the well wall by an optical trap (not shown). Spaced electrodes 76, 77 provide linear electric fields which induce dipoles 78, 79 in the microrotor/impeller 73 and well wall. This caused the impeller to rotate at a rotational velocity which depends upon the frequency of the applied electric fields. The rotating microrotor/impeller mixes the fluids.
FIG. 10 shows a schematic illustration of microchip including a plurality of fluid reservoirs, [0029] 71, 72, 73, 74 cooperating with microchannels 76, 77, 78 and 79. Different fluids can be applied to the fluid reservoirs and pumping and mixing along the channel can occur by employing the micropumps of the type described associated with each of the wells. Suitable detection means such as fluorescent detectors which detect labeled cells or molecules can be located along the channel. Alternatively, electrophotometric detectors can be placed along the channel to read changes in the chemical composition due to the reaction of chemicals which are mixed in the channels. It is apparent that other configurations of microchips can employ micropump/mixers in accordance with the present invention to pump, mix, direct and otherwise manipulate fluids in microchannels.
The foregoing descriptions of specific embodiments of the present invention are presented for the purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents. [0030]

Claims

What is claimed is:

1. A microfluidic device for moving a fluid comprising:

a polarizeable microrotor having a polarizability different than that of the fluid disposed in said fluid,

a polarizeable member electrostatically coupled to said microrotor,

spaced electrodes for applying an alternating electric field to said rotor and said member to induce alternating dipole fields in said rotor and coupled member whereby the coupled dipole fields interact to cause rotation of said microrotor to produce movement of said fluid.

2. A microfluidic device as in claim 1 in which said member is a second rotor.

3. A microfluidic device as in claim 1 wherein said fluid is disposed in a well whereby rotation of said microrotor mixes fluids in said well.

4. A microfluidic device as in claim 1 wherein said fluid is disposed in a microchannel and said member is a protrusion on the wall of said microchannel, whereby rotation of said microrotor pumps fluid along said channel.

5. A microfluidic device as in claim 1 wherein said fluid is disposed in a microchannel and said member is a second microrotor whereby rotation of said microrotor pumps fluid along said channel.

6. A microfluidic device including:

a dielectric motor,

a coupled member,

electrodes on opposite sides of said rotor and coupled member for applying electric fields to said rotor and coupled member, and

means for applying alternating voltages to said electrodes thereby inducing alternating dipole fields in said rotor and member which interact to cause rotation of said dielectric rotor.

7. A microfluidic device as in claim 6 in which said microrotor is disposed in a fluid whereby rotation of said microrotor causes movement of said fluid.

8. A microfluidic device as in claim 7 in which the microrotor is disposed in a microchannel and rotation of said microrotor pumps fluid along said channel.

9. A microfluidic device as in claim 7 in which the microrotor is disposed in a well to mix fluids in said well.

10. A microfluidic device as in claim 8 or 9 in which the coupled member is a protrusion in the wall of said microchannel or wall to position said microrotor.

11. A microfluidic device as in claim 8 or 9 in which said microrotor is positioned in coupled relationship to said member by optical tweezers.

12. A microfluidic device as in claim 6, 7, 8 or 9 in which said coupled member comprises a second microrotor and said microrotors are maintained in coupled relationship by optical tweezers.