U.S. patent application number 12/000897 was filed with the patent office on 2008-10-02 for microfluidic device and analyzing device using the same.
This patent application is currently assigned to Fluid Incorporated. Invention is credited to Shuzo Hirahara, Haruyuki Minamitani, Tomoyuki Tsuruta.
Application Number | 20080237046 12/000897 |
Document ID | / |
Family ID | 39639441 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080237046 |
Kind Code |
A1 |
Hirahara; Shuzo ; et
al. |
October 2, 2008 |
Microfluidic device and analyzing device using the same
Abstract
The conventional micropump and the conventional micromixer have
the following problems. In a mechanical or hydrodynamic method, the
structure of the inside of a flow path is complex so as to easily
cause clogging, and manufacturing cost is high, and dead volume is
large. Additionally, in an electrical method, the conventional
micropump or the conventional micromixer was incapable of operating
with a liquid having the concentration of a physiological saline
that is important in the medical or biological field although the
structure of the flow path is simple. These problems are solved by
applying an AC voltage to a pair of electrodes in which an
electrode-to-electrode gap between the pair of electrodes is
vertically arranged and by generating the flow of a fluid in the
direction opposite to gravity along the electrode-to-electrode gap.
A micropump (43, 44) can be realized especially by forming a
micro-sized flow path (11) in the vertical direction along the
electrode-to-electrode gap, and a micromixer (41) can be realized
by forming a micro-sized flow path (11) in the horizontal direction
to cross at right angle to the electrode-to-electrode gap.
Inventors: |
Hirahara; Shuzo;
(Yokohama-shi, JP) ; Tsuruta; Tomoyuki;
(Toyota-shi, JP) ; Minamitani; Haruyuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
Edwards Angell Palmer & Dodge LLP
1875 Eye Street, NW
Washington
DC
20006
US
|
Assignee: |
Fluid Incorporated
Yokohama-shi
JP
|
Family ID: |
39639441 |
Appl. No.: |
12/000897 |
Filed: |
December 18, 2007 |
Current U.S.
Class: |
204/600 |
Current CPC
Class: |
B01L 3/5027 20130101;
F04B 19/006 20130101; B01L 2300/0887 20130101; B01L 2300/088
20130101; B01F 13/0076 20130101 |
Class at
Publication: |
204/600 |
International
Class: |
B01J 19/08 20060101
B01J019/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2006 |
JP |
2006-340628 |
Claims
1. A microfluidic device comprising: a first substrate and a second
substrate that are disposed to face each other with a fluid between
the first and second substrates; and a pair of electrodes disposed
to face each other on a surface of the first substrate, the fluid
being in contact with the surface; wherein an
electrode-to-electrode gap between the pair of electrodes is
directed in a vertical direction, and wherein the fluid flows in a
direction opposite to gravity along the electrode-to-electrode gap
by applying an AC voltage to the pair of electrodes.
2. The microfluidic device of claim 1, wherein a micro-sized flow
path is formed that is in contact with the pair of electrodes and
that moves the fluid in a vertical direction.
3. The microfluidic device of claim 1, wherein a micro-sized flow
path is formed that is in contact with the pair of electrodes and
that moves the fluid in a horizontal direction.
4. The microfluidic device of claim 1, wherein the fluid flows in
circle between the first substrate and the second substrate.
5. An analytical instrument using the microfluidic device of claim
1.
6. A microfluidic device comprising: a first substrate and a second
substrate that are disposed to face each other with a fluid between
the first and second substrates; and a pair of electrodes disposed
to face each other on a surface of the first substrate, the fluid
being in contact with the surface; wherein an
electrode-to-electrode gap between the pair of electrodes is
directed diagonally to a vertical direction, and wherein the fluid
flows diagonally in a direction opposite to gravity along the
electrode-to-electrode gap by applying an AC voltage to the pair of
electrodes.
7. The microfluidic device of claim 6, wherein the pair of
electrodes is a first pair of electrodes in which the
electrode-to-electrode gap is directed in a vertical direction, a
second pair of electrodes in which the electrode-to-electrode gap
is directed diagonally with respect to the vertical direction, and
a third pair of electrodes in which the electrode-to-electrode gap
is directed diagonally symmetrically to the electrode-to-electrode
gap of the second pair of electrodes with respect to the vertical
direction, and wherein ends of the three pairs of electrodes are
disposed to be adjacent to each other so as to have a trifurcate
structure.
Description
BACKGROUND ART
[0001] 1. Technical Field
[0002] This invention relates to a microfluidic device that has
micro-sized flow paths dug into a glass substrate or a plastic
substrate so as to make an analysis or produce a reaction in the
flow paths by use of small amounts of samples and, more
specifically, to a micropump that generates a flow in the direction
of a flow-path axis while driving liquids in flow paths and to a
micromixer that stirs and mixes liquids together while generating a
swirling flow. Additionally, this invention relates to an
analytical instrument that uses liquid or a particulate material
flowing in liquids as a sample and that measures progress
information about reactions to a reagent or collects reaction
products.
[0003] 2. Description of the Related Art
[0004] In recent years, to reduce the amount of samples and save
process steps, a reactor or an analysis method that uses a
microfluidic device widely has spread. An electro-osmotic flow or a
pressure flow is widely used as a method for conveying liquids in
the microfluidic device. However, disadvantageously, many
high-voltage power supplies and many pumps will be needed, and
peripheral devices will be made large in size if micro-sized flow
paths are complexly structured. Additionally, there remain unsolved
problems, such as the "dead volume" problem of being incapable of
reducing the rate of useless samples by use of an electro-osmotic
flow or a pressure flow although the amount of samples to be used
has become small by micronizing a flow path.
[0005] To make the whole device compact, a pump formed in the
microfluidic device has been designed. Examples of such pumps
include a mechanical pump using a diaphragm shown in Patent
Document 1 and an electric pump using the action of an AC
electro-osmotic flow shown in Non-Patent Document 1. However, the
mechanical pump has defects one of which is the fact that special
materials, such as piezoelectric material and bimetal, are needed
and another one of which is the fact that many production processes
must be followed. Therefore, a rise in manufacturing costs is
caused, and a complex structure having great "dead volume" is
formed. Additionally, disadvantageously, clogging is liable to
occur, and a pulsating flow is caused. In contrast, the electric
pump advantageously has a simple structure. However, the electric
pump is not operated with the electrical conductivity (1.6 siemens
per meter (S/m)) of a physiological saline used and important in
medical and biological fields, and is only operated with the
electrical conductivity of a liquid which is equal to or less than
1/100 (i.e., about 10 millisiemens per meter (mS/m)) of that of the
physiological saline at a maximum.
[0006] On the other hand, the microfluidic device is characterized
in that a diffusion-controlled chemical reaction is accelerated by
a size effect, in that a slight amount of fluid is treated in a
tightly-sealed state, hence in that environmental pollution can be
prevented, in that a temperature-control response is swift, in that
a reaction field having no temperature distribution can be
obtained, and in that poisonous materials or an unstable, explosive
sample can be managed under safe environmental conditions.
Therefore, the microfluidic device also has been highly expected as
a microchemical reactor. However, disadvantageously, it is
difficult to secure a necessary reaction time, because one of the
restrictions imposed on the microfluidic device is that the flow
path, which is a reaction field, is short.
[0007] To hasten the reaction time, various mixers have been
designed. Examples of such mixers include a hydrodynamic mixer
(chaotic mixing) in which an obstacle is placed in a flow path as
shown in Patent Document 2 and an electric mixer that uses an
electrothermal effect or an AC electro-osmotic flow as shown in
Non-Patent Document 2 and Patent Document 3. However, the
hydrodynamic mixer needs a special microfabrication technique, and
has many production processes, and hence is high in manufacturing
costs. In addition, disadvantageously, the hydrodynamic mixer has a
complex flow path structure that easily causes clogging, and has
great flow path resistance resulting from the use of a flow force
for stirring. On the other hand, the electric mixer has the
advantage of having a simple structure as already described in the
pump. However, the electric mixer is not operated with the
electrical conductivity of a physiological saline used and
important in medical and biological fields, and is only operated
with the electrical conductivity of a liquid which is equal to or
less than 1/100 of that of the physiological saline at a
maximum.
[0008] [Patent Document 1] WO 98/51929
[0009] [Patent Document 2] WO 03/011443
[0010] [Patent Document 3] Japanese Unexamined Patent Application
Publication No. 2006-320877
[0011] [Non-Patent Document 1] A. B. D. Brown, C. G. Smith, and A.
R. Rennie: "Pumping of water with ac electric fields applied to
asymmetric pairs of microelectrodes", Physical Review E, vol. 63,
016305 (2000)
[0012] [Non-Patent Document 2] Marin Sigurdson, Dazhi Wang, and
Carl D. Meinhart: "Electrothermal stirring for heterogeneous
immunoassays", Lab on a Chip, vol. 5, pp. 1366-1373 (2005)
SUMMARY OF THE INVENTION
[0013] As described in the background art, the conventional
micropump and the conventional micromixer have the following
defects. According to a mechanical or hydrodynamic method, the
structure of the inside of a flow path is complex so as to easily
cause clogging, and manufacturing costs are high, and the dead
volume is great. Additionally, although an electrical method is
simple, the conventional micropump or the conventional micromixer
is incapable of operating with a liquid having the concentration of
a physiological saline that is important in the medical or
biological field.
[0014] The present invention solves the above problems by disposing
two flat electrodes used as a pair so that an
electrode-to-electrode gap therebetween is directed in the vertical
direction or in the diagonal direction and by generating a fast
flow ascending in the direction opposite to gravity along the
electrode-to-electrode gap while applying an AC voltage thereto.
The device of the present invention differs from the conventional
chip microfluidic device. In more detail, the device of the present
invention is used in a state of being vertically oriented, whereas
the conventional chip microfluidic device is used in a state of
being laid on a horizontally oriented plane. Especially, the
micropump of the present invention is realized by forming a
micro-sized flow path in the vertical direction along the
electrode-to-electrode gap, and a micromixer is realized by forming
a micro-sized flow path in the horizontal direction intersecting
with the electrode-to-electrode gap at right angles.
[0015] According to a method of using AC electrodes which is
superior in having a simple structure, the microfluidic device
provided by the present invention realizes a micropump or a
micromixer that exhibits sufficient performance even in a liquid
having a high electrical conductivity, such as a physiological
saline in which the conventional device does not operate.
[0016] The micropump of the present invention not only can perform
accurate setting by controlling an AC voltage applied to the
electrodes but also can operate even in a closed circulatory flow
path, and hence two micropumps can be disposed at two positions,
respectively, in the circulatory flow path. With this structure,
the selection from between the clockwise circulating direction and
the counterclockwise circulating direction, the flow speed, and the
stop position can be freely controlled with high accuracy by using
a simple electric circuit, and a user-friendly micropump can be
achieved.
[0017] Additionally, the micromixer of the present invention can
operate even in a state in which a flow in the direction of the
flow path is stopped. In the flow-stopped state, mixing in an
extremely short distance that corresponds to the size (about four
times as long as the width of the flow path) of two generated
eddies can be continuously performed for an arbitrary time, and
high-performance mixing in which the amount of samples consumed is
small can be achieved.
[0018] Additionally, an analytical instrument having less dead
volume is achieved by using a microfluidic device including the
micropump and the micromixer of the present invention.
[0019] This specification contains the contents mentioned in the
description and/or the drawings of Japanese Patent Application No.
2006-340628 that is the basis of the priority of the present
application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a partially enlarged view of a conventional
microfluidic device.
[0021] FIG. 2 is an enlarged view of a micropump of the present
invention.
[0022] FIG. 3 is an elevational view of a microfluidic device
provided with the micropump.
[0023] FIG. 4 is a photograph in which a flow line near an inflow
port of the micropump is visualized.
[0024] FIG. 5 is a graph showing characteristics of the
micropump.
[0025] FIG. 6 is an enlarged view of a micromixer of the present
invention.
[0026] FIG. 7 is an elevational view of a microfluidic device
provided with the micromixer.
[0027] FIG. 8 is a photograph in which eddies of the micromixer are
visualized.
[0028] FIG. 9 is a photograph in which eddies of the micromixer are
visualized when there is a flow in the horizontal direction.
[0029] FIG. 10 is an elevational view of the microfluidic device in
which stirring is performed by a space between parallel flat
substrates.
[0030] FIG. 11 is a general view of an analytical instrument of the
present invention.
[0031] FIG. 12 is an elevational view of a microfluidic device used
for the analytical instrument.
[0032] FIG. 13A to FIG. 13D are views explaining the operation of
the microfluidic device used in the analytical instrument.
[0033] FIG. 14 is a partially enlarged view of a detecting unit of
the analytical instrument.
[0034] FIG. 15 is a graph showing analysis results.
[0035] FIG. 16 is an elevational view of a microfluidic device in
which flows are combined together through spaces each of which lies
between parallel flat substrates.
[0036] FIG. 17 is an elevational view of a microfluidic device in
which a flow is divided by spaces each of which lies between
parallel flat substrates.
DETAILED DESCRIPTION OF THE INVENTION
[0037] A detailed description will be hereinafter given of
embodiments of a micropump and a micromixer by a microfluidic
device of the present invention and embodiments constituting an
analytical instrument.
Embodiment 1
[0038] First, a description will be given of a flow of a microfluid
generated by action from AC electrodes. An electrothermal effect
shown in Non-Patent Document 2 or a method of using the phenomenon
of an AC electro-osmotic flow shown in Patent Document 3 is known
as an electrical method of allowing a fluid to run in a micro-sized
space.
[0039] FIG. 1 is a partially enlarged view of a conventional
microfluidic device. The conventional microfluidic device is made
up of a substrate 100, a pair of electrodes 40, an AC power 31, and
sidewalls 18 forming a micro-sized flow path. The present inventors
performed experiments using the conventional microfluidic device
structured as shown in FIG. 1 in which the pair of electrodes 40
being in contact with the micro-sized flow path exist in a
horizontally oriented plane. In the experiments, saline solutions
differing in electrical conductivity (substantially proportional to
its concentration) were used, and an AC voltage of 5 MHz was
applied. In a saline solution whose electrical conductivity is
equal to or greater than several tens of mS/m, a flow that
corresponds to the above-mentioned two phenomena (i.e., the
electrothermal effect and the AC electro-osmotic flow) was not
observed. Instead, a significantly slow flow (whose speed is equal
to or less than several micrometers/s) which is rotated in a
direction opposite to the direction expected from the two
phenomena, was observed.
[0040] FIG. 2 is an enlarged view of a micropump of the present
invention. The micropump is the same in the basic structure as the
conventional microfluidic device, and is different in the direction
to be arranged therefrom. An experiment was performed as shown in
FIG. 2 in which the microfluidic device is vertically oriented and
in which the direction of an electrode-to-electrode gap of the pair
of electrodes 40 is set in the vertical direction. As a result, the
present inventors found that a fast flow (several hundred
micrometers/s to several millimeters/s) running in the direction of
the arrow in a micro-sized flow path 11 is generated. This flow,
which is different from the above-mentioned, two well-known
phenomena, occurs in a saline solution whose electrical
conductivity is equal to or greater than several tens of mS/m. In
this flow, the liquid between the electrodes always runs in the
direction opposite to gravity, and hence the present inventors
presumed that this flow is a buoyant flow generated by Joule heat
in the saline solution.
[0041] FIG. 3 is an elevational view of a microfluidic device
provided with the micropump. In an embodiment shown in FIG. 3, the
micropump 10 is formed by combining a closed circulatory
micro-sized flow path 11 with a pair of electrodes 40 arranged in
the vertical direction.
[0042] FIG. 4 is a photograph in which a flow line near an inflow
port of the micropump is visualized. The photograph of FIG. 4 is
one image obtained by pouring a physiological saline (whose
electrical conductivity is 1.6 S/m) having fluorescent beads (whose
particle size is 6 .mu.m) dispersed to visualize its flow into the
microfluidic device of FIG. 3 and by observing the flow running
below the pair of electrodes 40. It should be noted that this image
was obtained by superimposing photographed video images on each
other for five seconds, and was subjected to image processing to
obtain tracks of the fluorescent beads.
[0043] FIG. 5 is a graph showing characteristics of the micropump.
FIG. 5 shows a result of characteristics with respect to a voltage
applied to a pair of electrodes, which is obtained by measuring
speed from the length of each track of the fluorescent beads shown
in FIG. 4. The two characteristics were obtained by being measured
in two circulatory closed-loop flow paths one of which
(.smallcircle.) has a flow path cross-section having a depth of 650
.mu.m and a width of 850 .mu.m and the other one of which
(.diamond-solid.) has a flow path cross-section having a depth of
225 .mu.m and a width of 320 .mu.m, respectively. A flow velocity
of about 400 .mu.m/s and a flow velocity of about 150 .mu.m/s were
respectively obtained under an AC applied voltage of 5 MHz and 10V.
It is understood that the flow running in the circulatory
closed-loop flow path is a laminar flow (Hagen-Poiseuille flow)
having a parabolic velocity distribution in which the velocity is
maximized at the center of the flow path. Therefore, it was
confirmed that each microfluidic device of FIGS. 2 and 3 acts as a
micropump generating a flow that has a considerably fast velocity
(several hundred micrometers/s) and that is a nonturbulent, smooth
flow.
Embodiment 2
[0044] FIG. 6 is an enlarged view of a micromixer of the present
invention. The present inventors further performed an experiment
using a device structured so that a flow path extending in the
horizontal direction intersects the pair of electrodes 40 arranged
in the vertical direction as shown in FIG. 6. As a result, the
present inventors found that two eddies between which an
electrode-to-electrode gap lies occur.
[0045] FIG. 7 is an elevational view of a microfluidic device
provided with the micromixer. The present inventors performed an
experiment as followed. A Y-shaped flow path having two inflow
paths is produced as shown in FIG. 7, and a physiological saline is
poured from a first inflow port 12, whereas a physiological saline
containing fluorescent beads for experimental observation is poured
from a second inflow port 13. The fluorescent beads in a
laminar-flow state flowing near the lower wall surface in the flow
path moved close to the upper wall surface, opposite to the lower
one of the flow path, at a fast speed when the fluorescent beads
passed through the electrode-to-electrode gap (50 .mu.m) of the
pair of electrodes 40. From this fact, it was understood that the
flow crossing the flow path between the two eddies is considerably
fast, and hence the device can be used as a micromixer 30.
[0046] The micromixer 30 of the present invention can generate
eddies regardless of the presence or absence of a flow in the
direction of the flow path. Therefore, if the flow is stopped in a
state in which a sample is kept within a distance (about four times
as long as the flow path width) equal to twice as long as eddy,
mixing and stirring can be continuously performed for a long
time.
[0047] FIG. 8 is a photograph in which eddies of the micromixer are
visualized. The photographic image of FIG. 8 is obtained by
visualizing eddies generated in the state of stopping the flow by
use of the fluorescent beads. As can be understood from FIG. 8, if
the micromixer of the present invention is used, small amounts of
sample plugs that correspond to a length which is about four times
as long as the flow path width can be treated. Therefore, a
reactor, an inspection device, or an analytical instrument having
small dead volume can be easily realized.
[0048] FIG. 9 is a photograph in which eddies of the micromixer are
visualized when there is a flow in the horizontal direction. The
photograph of FIG. 9 was taken in a state in which the micromixer
was set under the presence of a flow of 5 .mu.L/minute. As shown in
FIG. 9, it is apparent that the micromixer according to this
embodiment operates under the presence of such a flow, and the
micromixer can, of course, be used as a part of a continuous
on-line process.
[0049] In the two embodiments mentioned above, the two examples
were shown. In one of the two examples, the direction of a part of
the micro-sized flow path being in contact with the pair of
electrodes 40 is parallel to, i.e., intersects at an angle of zero
degrees with that of the electrode-to-electrode gap lying between
the pair of electrodes 40, and, in the other example, the direction
of a part of the micro-sized flow path being in contact therewith
is perpendicular to, i.e., intersects at right angles with that of
the electrode-to-electrode gap lying therebetween. However, the
present invention is not limited to these two angles. If these
intersect with each other at an angle of degrees greater than zero
degrees and smaller than 90 degrees, it is possible to realize a
device concurrently having two functions one of which is to pump
fluids flowing in the flow path in the direction of the axis of the
flow path and the other one of which is to move fluids flowing in
the flow path in the vertical direction and mix these fluids
together.
[0050] Additionally, in the two embodiments mentioned above, a
description was given of the two slender flow paths one of which is
a circulatory closed-loop type and the other one of which is a
circulatory open-loop type in which fluids flow from an inflow end
to an outflow end. However, the gist of the present invention does
not reside in the imposition of limitations on the width of the
flow path. If the micropump and the micromixer of the present
invention are structured to have effective operations, any kind of
flow path can be employed.
[0051] FIG. 10 is an elevational view of the microfluidic device in
which stirring is performed by a space between parallel flat
substrates. For example, in FIG. 10, a sample substrate 45 having a
surface onto which a sample is applied and fixed and an electrode
substrate 46 having a surface onto which a pair of electrodes 40
are patterned by optical lithography are allowed to face each
other, and a space between the parallel flat substrates which is
formed by sandwiching a spacer 47 ranging from about several tens
of micrometers to about several hundred micrometers therebetween is
used as a flow path.
[0052] In a flow path having a two-dimensional extension as in the
example of FIG. 10, the flow of a liquid ascending along the
electrode-to-electrode gap of the pair of electrodes 40 descends at
a position away from the pair of electrodes 40, and circulates in
the space between the parallel flat substrates. In an analysis of a
biologic sample, there are many processes requiring a long-time
reaction, such as gene hybridization, enzyme reaction, and
antigen-antibody reaction. The use of the microfluidic device
provided with the pair of electrodes 40 of FIG. 10 makes it
possible to stir small amounts of samples in the space between the
parallel flat substrates. As a result, the reaction rate is
accelerated by stirring, and hence the process time for inspection
or analysis can be shortened. This device is effective especially
for array chips used to analyze biological materials, such as gene
chips or protein chips.
[0053] As described in the above embodiments, according to the
present invention, it is possible to realize a micropump and a
micromixer both of which are easily controlled in a simple
structure and are operated with liquids (including a physiological
saline) which has an electrical conductivity of 10 mS/m or more.
Additionally, the present invention can be applied to all
microfluidic devices that can use the micropump and the micromixer.
Still additionally, the present invention can be applied to all
inspection devices and analytical instruments that can be used.
Concrete examples will be hereinafter shown.
Embodiment 3
[0054] FIG. 11 is a general view of an analytical instrument
provided with the microfluidic device of the present invention. In
this embodiment, an example is shown in which the present invention
is applied especially for a platelet aggregation test by which a
platelet clump size is measured, and the structure and the
operation of the instrument will be described.
[0055] As a preprocessing step for inspection, a platelet sample of
platelet-rich plasma (PRP) or platelet-poor plasma (PPP) is
prepared from the blood which has been drawn from a subject and
mixed into 3.8% citric-acid solution, and is incubated at
37.degree. C. equal to the body temperature in a sample reservoir
(not shown). On the other hand, 0.3 .mu.M epinephrine is produced
as a platelet-aggregating agent, and is set in a reservoir for the
aggregating agent provided at a liquid supply pump 16.
[0056] The plasma of the incubated platelet sample is replaced with
a physiological saline, and then a small amount of the sample is
dropped into an open well provided in a microfluidic device 1 by
use of a pipet. This microfluidic device 1 is vertically oriented,
and is set on a stage of a microscope 32. The liquid supply pump 16
that supplies a platelet-aggregating agent and a suction pump 17
that sucks out a waste fluid or the like are connected to the
microfluidic device 1 through tubes. The AC power 31 that drives
the micropump and the micromixer too is connected to the
microfluidic device 1 through three electric cables.
[0057] The state and the change of the platelet in the microfluidic
device are converted into an electric signal by a CCD camera 33
disposed on the microscope 32, and is input to a data acquiring and
analyzing device 34 that performs image analysis, image processing,
image storage, and the like. A process controller 35 controls a
process necessary for inspection according to a program through
interfaces with the liquid supply pump 16, the suction pump 17, the
AC power 31, and the data acquiring and analyzing device 34.
[0058] FIG. 12 is an elevational view of a microfluidic device used
for the analytical instrument. The structure of the microfluidic
device used in this embodiment will be described with reference to
FIG. 12. The first inflow port 12 is an open well, and a sample is
injected through this port according to, for example, a method of
dropping it by use of a pipet. The second inflow port 13 and the
outflow port 14 are connected to the liquid supply pump 16 and the
suction pump 17 of FIG. 11, respectively.
[0059] The micro-sized flow path 11 has a circulating-flow-path
structure, and includes a flow path intersection 15 made up of a
flow path extending from the first inflow port 12 and a flow path
extending from the second inflow port 13, the micromixer 41
mentioned in the second embodiment of the present invention, the
micropump 43 of the present invention circulating in the clockwise
direction, a T-shaped intersection flow path 19 leading to the
outflow port 14, and the micropump 44 of the present invention
circulating in the counterclockwise direction which are arranged in
this order.
[0060] FIG. 13A to FIG. 13D are views explaining the operation of
the microfluidic device used in the analytical instrument. Next,
the operation of the analytical instrument will be described
according to steps programmed by the process controller of FIG. 11.
A description thereof will be started from a step in which all flow
paths of the microfluidic device of FIG. 12 are pre-filled with a
physiological saline 20. Although various methods can be proposed
as procedures for filling the flow paths with this physiological
saline, a description of this is omitted here. The cross-section of
the circulatory flow path used here is a rectangle having a width
of 400 .mu.m and a depth of 320 .mu.m.
[0061] First, a drop of platelet sample 22 (20 to 50 .mu.L) is put
from the pipet into the first inflow port 12 that is an open well,
and an inspection process is started. FIG. 13A shows a state near
the flow path intersection 15 when the inspection process is
started.
[0062] Thereafter, when the liquid supply pump 16 (2 .mu.L/minute)
and the suction pump 17 (2 .mu.L/minute) are turned on at the same
time, a physiological saline 20 flows out from the outflow port 14,
and a platelet-aggregating agent 23 having the same volume flows in
from the second inflow port 13. After six seconds, a plug of the
platelet-aggregating agent 23 of 1500 .mu.m is generated centering
the flow path intersection 15 as shown in FIG. 13B.
[0063] Thereafter, when only the liquid supply pump 16 is turned
off (in the state in which six seconds have elapsed), the platelet
sample 22 is injected from the first inflow port 12, which is an
open well, through the cross intersection flow path this time.
After three seconds, a plug is generated in which the platelet
sample 22 of 750 .mu.m is sandwiched at the center of the
platelet-aggregating agent 23 whose length is 1500 .mu.m as shown
in FIG. 13C. At this stage, the suction pump 17 is also turned
off.
[0064] Thereafter, a terminal of the AC power 31 that is connected
to the micropump 44 used to circulate liquids in the
counterclockwise direction is turned on, and the plug including the
sample is moved toward the micromixer. This state is shown in FIG.
13D.
[0065] When the plug including the sample reaches the micromixer
41, a terminal of the AC power 31 that is connected to the
micromixer 41 is turned on, and the platelet sample 22 and the
platelet-aggregating agent 23 start being mixed and stirred
together.
[0066] FIG. 14 is a partially enlarged view of a detecting unit of
the analytical instrument. A change in the size of the clump of the
platelet with the lapse of the stirring time can be observed with a
monitor 36 via the microscope 32 and the CCD camera 33 as shown in
FIG. 14. At the same time, measurement and analysis can be
performed for succeeding steps.
[0067] FIG. 15 is a graph showing analysis results. FIG. 15 shows
an analysis example of a comparison between the particle-size
distribution of the platelet aggregate obtained when the platelet
sample and the aggregating agent start being mixed together and the
particle-size distribution of the platelet aggregate obtained when
three minutes elapse after being mixed.
[0068] If the micropump 43, which circulates liquids in the
clockwise direction, is used together with the micropump 44, which
circulates liquids in the counterclockwise direction, as a pair,
the micropump 43 will be useful especially when accurate position
control is required although this has not been described here. For
example, the micropump 43 is useful when the position of a sample
plug is caused to exactly coincide with the electrode-to-electrode
gap of the micromixer 41 while performing fine position control or
when an air plug generated during preparation for filling all flow
paths with a physiological saline or a plug of a specific reaction
product is led to the T-shaped flow path of the outflow port so as
to extract the plug therefrom.
[0069] The volume of the platelet sample and the volume of the
platelet-aggregating agent used for the measurement in this
embodiment are 0.1 .mu.L and 0.2 .mu.L, respectively. As described
above, according to the present invention, an analytical instrument
that is extremely small in the amount of samples consumed and in
dead volume can be realized.
[0070] Although the aggregometer using a platelet sample, for
example, was disclosed in the embodiment of the analytical
instrument of the present invention, the biological materials to
which the microfluidic device proposed here are applied is not
limited to platelets. The biological materials include all of
biochemical materials and biologic samples each of which is microns
in diameter or smaller than microns, such as gene, antibody,
protein, virus, cell, blood, and bacteria.
[0071] Additionally, according to the gist of this proposal, the
sample used in the analytical instrument is not limited to
biological materials. All chemicals that require a mixer that
causes reactions in microchannels can be used in the analytical
instrument, and all solutions and dispersion liquids that are
required to be conveyed by a pump in microchannels can be used in
the analytical instrument.
[0072] FIG. 16 and FIG. 17 are views each of which shows a
microfluidic device structured to have a space (sandwiched between
the electrode substrate 46 and a substrate 50 facing the electrode
substrate 46) between two parallel wall surfaces between which a
spacer 47 is placed, as in FIG. 10. As general properties, in
proportion to a decrease in space, it becomes more difficult for a
fluid in such a flow path to flow. The reason is that the ratio
between (two-dimensional) viscous drag that a fluid extending in
the direction of a plane receives from the wall surfaces and the
(three-dimensional) volume of the fluid becomes greater in
proportion to the narrowing of a space. Therefore, to generate a
flow, an extremely great force or pressure is required to be
applied. However, the present inventors found that the following
two characteristics will appear if a pair of electrodes are
disposed on the wall surfaces.
[0073] The first characteristic is that the speed of an ascending
flow generated in the electrode-to-electrode gap is not reduced
even if the gap is 200 .mu.m or less. Without being limited to
this, there is a case in which the speed is increased depending on
conditions. The second characteristic is that, if the
electrode-to-electrode gap of the pair of electrodes on the wall
surfaces is arranged to be diagonally directed (i.e., in a
direction rotated from the vertical direction) while maintaining
the direction (vertical direction) of the parallel wall surfaces, a
flow generated in the electrode-to-electrode gap is allowed to run
in the diagonal direction in the same way along the
electrode-to-electrode gap directed diagonally. However, the speed
of the flow becomes slower in proportion to an increase in angle,
and becomes approximately zero when the flow is directed in the
horizontal direction (i.e., at an angle of 90 degrees from the
vertical direction).
Embodiment 4
[0074] FIG. 16 is an elevational view of a microfluidic device in
which flows are combined together through spaces each of which lies
between parallel flat substrates. Next, an example of a device
using the two characteristics mentioned above will be hereinafter
shown. The embodiment shown in FIG. 16 achieves the combining of
wide flows by an action generated by pairs of electrodes arranged
to have the shape of the reversal of the letter Y.
[0075] The pairs of electrodes in this embodiment are disposed such
that a second pair of electrodes 52 and a third pair of electrodes
53 are disposed diagonally open at the lower end of a first pair of
electrodes 51 directed in the vertical direction. When an AC
voltage is applied to all of the three pairs of electrodes, a
diagonal flow running at a speed that has undergone vector
resolution according to an angle with respect to the vertical
direction is generated in the electrode-to-electrode gap of the
second pair of electrodes 52 and in the electrode-to-electrode gap
of the third pair of electrodes 53. Additionally, a fast
vertically-ascending flow is generated in the first pair of
electrodes 51. As a result of the combination of these operations,
the comparatively slow diagonal flow generated by the second and
third pairs of electrodes 52 and 53 can join with even slower flows
running in the planar flow paths, and can act like a funnel that
sends the resulting flow into the space between the first pair of
electrodes 51 between which a fast flow is running.
[0076] FIG. 17 is an elevational view of a microfluidic device in
which a flow is divided by spaces each of which lies between
parallel flat substrates. The embodiment shown in FIG. 17 achieves
a function to give selective distribution/switching to a flow in
accordance with some kind of information concerning a sample
conveyed to a fast flow running between the first pair of
electrodes 51 in a state in which the arrangement of the electrodes
shown in the above embodiment is turned upside down. In this
embodiment, for example, particles emitting fluorescence are
optically detected, and, based on information thereabout, a voltage
to be applied to the second and third pairs of electrodes 52 and 53
is turned on/off or is switched in accordance with a timing at
which the particles pass through, and, as a result, only necessary
particles can be collected at a specific laminar flow position. In
FIG. 17, the AC voltage to be applied to the third pair of
electrodes 53 is in an OFF state, whereas the first and second
pairs of electrodes 51 and 52 are in an ON state, and the flow is
running in the right upward direction while being guided by the
electrodes to which a voltage has been applied.
[0077] In each of the embodiments of FIGS. 16 and 17, the device
has a structure in which two of the four sides of the device are
closed with the spacer, whereas the other two are brought into an
open state, and a fluid is supported by a capillary force of the
fluid. However, the present invention is achieved regardless of the
structure or the number of spacers to be used. Therefore, a spacer
that surrounds the device as shown in the embodiment of FIG. 10 may
be used, and spacers having any other shapes may be used.
[0078] As described in the above embodiments, according to the
present invention, it is possible to achieve a microfluidic device
having a simple structure in which flows are combined together
along electrodes subjected to patterning on wall surfaces, are then
guided at a fast flow speed, and are distributed or classified,
without providing partitions in a flow path of a narrow space lying
between two parallel planes. Additionally, fluids can be
manipulated unlike in a conventional microfluidic device that uses
a thin flow path, and hence the degree of freedom of design of the
microfluidic device can be further widened.
[0079] The entire contents of all of the publications, the patents,
and the patent applications cited in this specification are hereby
incorporated by reference.
INDUSTRIAL APPLICABILITY
[0080] As described above, the present invention achieves a
micropump and a micromixer each of which has a simple structure,
and provides a microfluidic device that includes the micropump and
the micromixer each of which serves as a basic part of the
microfluidic device. Additionally, the present invention can be
applied to all instruments, apparatuses, or machines using the
microfluidic device, such as a chemical analytical instrument, a
biological material inspection apparatus (.mu.TAS), a microchemical
reactor, and a micromachine (MEMS).
* * * * *