U.S. patent application number 10/283100 was filed with the patent office on 2003-04-03 for method and apparatus for magnetically separating selected particles, particularly biological cells.
Invention is credited to Davidson, Chaim, Klein, Ofer, Lamish, Ahron.
Application Number | 20030062314 10/283100 |
Document ID | / |
Family ID | 11071507 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030062314 |
Kind Code |
A1 |
Davidson, Chaim ; et
al. |
April 3, 2003 |
Method and apparatus for magnetically separating selected
particles, particularly biological cells
Abstract
A method and apparatus for magnetically separating target
particles of a selected type from a sample in order to produce a
concentration of the target particles in the sample, or a depletion
of the sample with respect to the target particles, by producing a
sample mixture of the sample with magnetic particles having a
selective affinity to magnetically stain the target particles;
producing a flow of a buffer liquid through a tube which includes
an inlet connectable to a source of buffer liquid, and an outlet
for the buffer liquid; after a flow of the buffer liquid has been
produced through the tube, introducing the sample mixture into the
buffer liquid flowing through the tube such that the buffer liquid
forms a continuous liquid carrier for the sample mixture as both
are fed through the tube; and applying a magnetic field across the
tube at a magnetizing station therein to cause the
magnetically-stained target particles to be separated and retained
in the buffer liquid within the tube at the magnetizing
station.
Inventors: |
Davidson, Chaim; (Merom
Hagalil, IL) ; Klein, Ofer; (Galil Elion, IL)
; Lamish, Ahron; (Ramat Gan, IL) |
Correspondence
Address: |
SOL SHEINBEIN
c/o ANTHONY CASTORINA
SUITE 207
2001 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
11071507 |
Appl. No.: |
10/283100 |
Filed: |
October 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10283100 |
Oct 30, 2002 |
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09700218 |
Nov 13, 2000 |
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6482328 |
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09700218 |
Nov 13, 2000 |
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PCT/IL99/00255 |
May 13, 1999 |
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Current U.S.
Class: |
210/695 ;
210/198.1; 210/222 |
Current CPC
Class: |
B03C 1/035 20130101;
B03C 1/005 20130101; B03C 1/30 20130101 |
Class at
Publication: |
210/695 ;
210/198.1; 210/222 |
International
Class: |
C02F 001/48 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 1998 |
IL |
124,514 |
Claims
What is claimed is:
1. A method of magnetically separating target particles of a
selected type from a sample in order to produce a concentration of
the target particles in the sample, or a depletion of the sample
with respect to the target particles, comprising: producing a
sample mixture of said sample with magnetic particles having a
selective affinity to magnetically stain said target particles;
feeding a buffer liquid through a tube which includes an inlet
connectable to a source of buffer liquid, and an outlet for the
buffer liquid; introducing said sample mixture into the buffer
liquid such that the buffer liquid forms a continuous liquid
carrier for said sample mixture as both are fed through said tube;
and applying a magnetic field across said tube at a magnetizing
station therein to cause the magnetically-stained target particles
to be separated and retained in the buffer liquid within the tube
at the magnetizing station.
2. The method according to claim 1, wherein said sample mixture is
introduced into said buffer liquid at a location between the inlet
end of the tube and said magnetizing station.
3. The method according to claim 1, wherein the target particles
which are magnetically-stained by the magnetic particles in said
sample mixture, separated, and retained in the buffer liquid within
the tube at the magnetizing station, are subsequently removed from
the tube by terminating the introduction of said sample mixture
into the buffer liquid, and the application of the magnetic field
across the tube, while the buffer liquid is fed through the tube to
flush out said magnetically-stained target particles with the
buffer liquid.
4. The method according to claim 1, wherein said buffer liquid and
sample mixture are gravity fed through said tube into a receiving
container.
5. The method according to claim 4, wherein a vacuum is applied to
said receiving container for controlling the feeding of said buffer
liquid and sample mixture into said receiving container.
6. The method according to claim 4, wherein a positive pressure is
applied to said tube to control the feeding of said buffer liquid
and sample mixture into said receiving container.
7. The method according to claim 1, wherein said target particles
are selected biological cells in said sample.
8. The method according to claim 7, wherein said sample is a blood
sample, and said target cells are a selected type of lymphocyte in
the blood sample.
9. The method according to claim 1, wherein said magnetic particles
mixed with the sample are in the form of magnetic microbeads.
10. The method according to claim 1, wherein said magnetic field is
controlled to produce a predetermined field intensity.
11. Apparatus for magnetically separating target particles of a
selected type from a sample in order to produce a concentration of
the target particles in the sample, or a depletion of the sample
with respect to the target particles, comprising: a tube for
feeding a buffer liquid from a buffer liquid supply at an inlet end
of the tube to an outlet end of the tube; an input port for
inputting into said tube a buffer liquid and a sample mixture of
said sample with magnetic particles having a selective infinity to
magnetically stain said target particles, such that the buffer
liquid forms a continuous liquid carrier for the
magnetically-stained target particles as the buffer liquid is fed
through the tube; magnetic field producing means for producing a
magnetic field across the tube at a magnetizing station therein to
cause the magnetically-stained target particles to be separated and
retained in the buffer liquid within the tube at said magnetizing
station; and a container located at the outlet end of the tube for
receiving the buffer liquid and the sample depleted of the target
particles.
12. The apparatus according to claim 11, wherein said input port
includes a first connection connecting the buffer liquid supply to
the inlet end of the tube, and a second connection for introducing
the sample mixture into said buffer liquid at a location between
the said inlet end of the tube and said magnetizing station.
13. The apparatus according to claim 11, wherein said container is
located below said inlet end of the tube such that the buffer
liquid and sample mixture are gravity fed through said tube to said
container.
14. The apparatus according to claim 13, wherein said container is
connected to a suction source for controlling the feeding of the
buffer liquid and sample mixture through the tube.
15. The apparatus according to claim 13, wherein said tube includes
a positive pump to control the feeding of the buffer liquid and
sample mixture through said tube.
16. The apparatus according to claim 11, wherein said apparatus
further comprises a second container to be located at the outlet
end of the tube in place of said first-mentioned container; and
wherein both the application of the magnetic field, and the
introduction of said sample mixture into the buffer liquid, are
terminable to cause the buffer liquid being fed through the tube to
flush-out the magnetically-stained target particles into said
second container.
17. The apparatus according to claim 11, wherein said apparatus
further comprises an air bubble sensor for sensing the presence of
air in the buffer liquid fed through said tube, an air bubble
sensor for sensing the presence of air in the sample mixture fed to
said tube, and a controller controlled by said sensors for
interrupting the flow of said buffer or sample mixture upon the
detection of an air bubble therein.
18. The apparatus according to claim 11, wherein said magnetic
field is produced by magnets mounted on magnetizable core elements
defining a closed magnetic circuit including a first air gap
between the magnets, and a second air gap between the magnetizable
core elements; said tube passing through both said air gaps.
19. The apparatus according to claim 18, wherein said magnetizable
core elements also define a third air gap, through which said tube
also passes.
20. The apparatus according to claim 11, wherein said magnetic
field producing means includes permanent magnets which are
physically movable from the vicinity of the tube to terminate the
application of the magnetic field across the tube at said
magnetizing station.
21. The apparatus according to claim 11, wherein said magnetic
field producing means includes an electromagnet which is
electrically deenergisable to terminate the application of the
magnetic field across the tube at said magnetizing station.
22. The apparatus according to claim 11, further including a
control system for controlling the magnetic to produce a
predetermined field intensity.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
magnetically separating particles of a selected type (hereinafter
called "target particles") from a sample in order to produce a
concentration of the target particles in the sample, and or a
depletion of the sample with respect to the target particles. The
invention is particularly useful for magnetically separating
biological cells of a selected type, e.g., a selected type of
lymphocyte cell in a blood sample, and is therefore described below
especially with respect to such applications.
[0002] A large number of applications involving the magnetic
separation of biological cells are described in the literature, for
example in U.S. Pat. No. 4,710,472 and the many publications cited
therein, which are hereby incorporated by reference. Many such
applications require not only the separation of one or more
specific types of cells (hereinafter called "target cells"), but
also the maintenance of the quality of the cell membranes in the
target cells, and/or in the untargetted cells. Thus, in a positive
selection process, the target cells are separated from a sample for
examination or use for research, diagnostic or clinical purposes;
whereas in a depletion process, the sample is depleted of the
target cells for examination or use of the untargetted cells. The
separation of target cells from the untargetted cells, and the
maintenance of the membranes of both the target cells and
untargetted cells, are particularly important in research presently
being conducted with lymphocyte populations and their role in the
early detection of cancer.
[0003] One technique in present use for the separation of
biological cells utilizes the MiniMACS Separation Columns (Miltenyi
Biotec GmbH). This technique uses paramagnetic microbeads which are
extremely small, about 50 nm in diameter, i.e., about one milion
times smaller in volume than that of eukatyotic cells, compared to
the size of a virus. Such magnetic microbeads are produced with
selective affinities for certain cells, i.e., the target cells,
such that they magnetically label or stain the target cells. The
sample is introduced into a magnetic separation column including a
liquid-pervious magnetic body, e.g., steel wool or mesh, and a
magnetic field is applied across the column such that the
magnetically stained cells are retained in the liquid-pervious
magnetic body of the column, while the unstained cells pass through
the column. In this known process, however, it was found that the
membranes of the cells are excessively damaged by the
liquid-pervious magnetic body, which reduces the effectiveness of
the technique for research or clinical purposes.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide a method of
magnetically separating target particles of a selected type from a
sample in a manner which causes less damage to the membrane than
the above described known technique. Another object of the present
invention is to provide apparatus for magnetically separating
target particles in accordance with the novel method.
[0005] According to one aspect of the present invention, there is
provided a method of magnetically separating target particles of a
selected type from a sample in order to produce a concentration of
the target particles in the sample, or a depletion of the sample
with respect to the target particles, comprising: producing a
sample mixture of the sample with magnetic particles having a
selective affinity to magnetically stain the target particles;
feeding a buffer liquid through a tube which includes an inlet
connectable to a source of buffer liquid, and an outlet for the
buffer liquid; introducing the sample mixture into the buffer
liquid such that the buffer liquid forms a continuous liquid
carrier for the sample mixture as both are fed through the tube;
and applying a magnetic field across the tube at a magnetizing
station therein to cause the magnetically-stained target particles
to be separated and retained in the buffer liquid within the tube
at the magnetizing station.
[0006] Such a method is particularly useful in a depletion process,
wherein a sample depleted of the target particles is to be produced
for diagnostic examination, research, or clinical purposes.
[0007] According to further features in the described preferred
embodiments, the magnetically-stained target particles in the
sample mixture, which are separated and retained in the buffer
liquid within the tube at the magnetizing station, are subsequently
removed from the tube by terminating the introduction of the sample
mixture into the buffer liquid and the application of the magnetic
field across the tube, while the buffer liquid is fed through the
tube to flush out the magnetically-stained target particles with
the buffer liquid. Such a method is particularly useful in a
positive selection process, wherein the target particles are to be
separated and used for diagnostic examination, research or clinical
purposes.
[0008] According to another aspect of the present invention, there
is provided apparatus for magnetically separating target particles
of a selected type from a sample in order to produce a
concentration of the target particles in the sample, or a depletion
of the sample with respect to the target particles, comprising: a
tube for feeding a buffer liquid from a buffer liquid supply at an
inlet end of the tube to an outlet end of the tube; an input port
for inputting into the tube a buffer liquid and a sample mixture of
the sample with magnetic particles having a selective affinity to
magnetically stain the target particles, such that the buffer
liquid forms a continuous liquid carrier for the
magnetically-stained target particles as the buffer liquid is fed
through the tube; magnetic field producing means for producing a
magnetic field across the tube at a magnetizing station therein to
cause the magnetically-stained target particles to be separated and
retained in the buffer liquid within the tube at the magnetizing
station; and a container located at the outlet end of the tube for
receiving the buffer liquid and the sample depleted of the target
particles.
[0009] Where the apparatus is to be used in a positive selection
process, the apparatus further comprises a second container which
can be located at the outlet end of the tube in place of the
first-mentioned container; in addition, the application of the
magnetic field, and the inputting of the mixture into the buffer
liquid, are both terminated to cause the buffer liquid fed through
the tube to flush out the magnetically-stained target particles
into the second container.
[0010] Such a method and apparatus have been found to enable the
separation of selected types of particles, (target particles),
particularly biological cells (target cells), without causing undue
damage to either the target particles or the untargetted particles.
Thus, the buffer liquid, which forms a continuous liquid carrier
for both the target particles and the untargetted particles,
produces a constant liquid volume which physically supports both
types of particles (or cells) during both phases of the process,
thereby minimizing damage to both types of particles during both
phases.
[0011] While the method and apparatus of the present invention are
particularly useful for separating selected types of biological
cells, such method and apparatus may also be used for separating
other types of particles, e.g., selected proteins. Also, while the
described method and apparatus preferable use the
commercially-available magnetic microbeads, it will be appreciated
that other magnetic particles having a selective affinity for the
target particles may be used to magnetically stain or label the
target particles.
[0012] Further features and advantages of the invention will be
apparent from the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0014] FIG. 1 schematically illustrates the basic elements of one
form of apparatus constructed in accordance with the present
invention;
[0015] FIG. 2 schematically illustrates a system including
apparatus similar to that of FIG. 1 and the main controls
therefor;
[0016] FIG. 3 illustrates the basic elements of a second form of
apparatus constructed in accordance with the present invention;
[0017] FIG. 4 is a sectional view along line 4-4 of FIG. 3;
[0018] FIG. 5 is a sectional view along line 5-5 of FIG. 4;
[0019] FIG. 6 is an exploded three-dimensional view illustrating
the magnet holders, and their corresponding magnets, at one side of
the magnetizing station in the apparatus of FIGS. 3-5; and
[0020] FIG. 7 illustrates another apparatus constructed in
accordance with the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] The apparatus illustrated in FIG. 1 is particularly useful
for magnetically separating certain types of target cells, such as
lymphocytes, red blood cells, and/or macrophages, from a blood
sample.
[0022] The illustrated apparatus includes a sample container 10 to
contain the blood sample. Before or after the blood sample is
introduced into container 10, it is mixed with magnetic particles,
preferably the commercially-available magnetic microbeads, having a
selective affinity to magnetically stain or label the target cells
in the blood sample within container 10.
[0023] The apparatus further includes another container 11 which
serves as a supply of a buffer liquid to be used in the magnetic
separation process. The buffer liquid in container 11 may be any of
the commercially-available buffer liquids, such as normal saline
solution, PBS, and the like.
[0024] The apparatus illustrated in FIG. 1 further includes a feed
tube 12 for feeding the buffer liquid from the buffer container 11
through a magnetizing station 13 to a receiving container 14. In
the embodiment of FIG. 1 the feeding of the buffer liquid via feed
tube 12 is effected by gravity and a vacuum. For this purpose, the
two supply containers 10 and 11 are located above the receiving
container 14; and the receiving container 14 includes a vacuum tube
15 communicating at one end with the interior of the receiving
container, and at the opposite end with a vacuum source 16.
[0025] The blood sample within the sample container 10 includes the
magnetically-stained target cells as well as the non-targetted
cells. The blood sample is introduced via line 17 into an input
port 12a in the feed tube 12 at a location upstream of the
magnetizing station 13. However, before the sample is introduced
into the feed tube 12, the feed tube is first filled with degassed
buffer liquid from container 1, and a predetermined flow rate is
effected. The flow rate is preferably less than one drop per
second; a preferred flow rate is 6-8 drops per minute. Presetting
the flow rate may be effected by controlling the vacuum source 16,
or by controlling one or more valves as will be described more
particularly below with respect to FIG. 2.
[0026] The buffer liquid from container 11 thus serves as a
continuous liquid carrier for the magnetically-stained target cells
and non-target cells in the blood sample introduced from container
10 via the input port 12a, as both the buffer liquid and the
mixture, including the target cells and non-targetted cells
therein, flow via the feed tube 12 through the magnetizing station
13. Magnets 18 at the magnetizing station 13 apply a magnetic field
across the feed tube 12 sufficient to separate and retain the
magnetically-stained target cells within the buffer liquid at the
magnetizing station 13 as the buffer liquid, with the
non-magnetized cells and other constituents of the blood sample,
flows through the output end of the feed tube 12 into the receiving
container 14. The receiving container 14 thus receives the buffer
liquid together with the non-targetted cells of the blood sample,
since the magnetically-stained target cells of the blood sample
(including the magnetic particles mixed therein) are held in stasis
by the magnetic flux produced by the magnets 18 in the magnetizing
station 13.
[0027] The contents of the receiving container 14 thus constitute
the results of a depletion process performed on the original sample
since these contents include all the original constituents of the
sample except for the magnetically-stained target cells (and the
magnetic particles added to the original sample in container 10)
which are separated and retained in the magnetizing station 13.
Accordingly, the contents of container 14 may be examined or used
for diagnostic, research, or clinical purposes in the same manner
as when using the results of any other corresponding depletion
process performed on the original sample.
[0028] If it is also desired to perform a positive selection
process on the original sample (i.e., to use the separated target
cells for diagnostic, research, or clinical purposes), this may be
done by: (a) continuing to feed the buffer liquid through tube 12;
(b) terminating the supply of the mixture from the sample container
10 and the application of the magnetic field at the magnetizing
station 13; and (c) replacing the receiving container 14 with
another receiving container (not shown) to receive the target cells
which are flushed-out by the buffer liquid fed through the feed
tube 12. Generally, it would be preferable, after terminating the
introduction of the sample from the sample container 10, to delay
for a short time the termination of the application of the magnetic
field at the magnetizing station 13 and the switch-over of the two
containers, to enable the buffer, liquid to rinse-out the
magnetically-stained target particles retained in the magnetizing
station 13 before such particles are flushed-out to the second
receiving container.
[0029] Magnets 18 at the magnetizing station 13 may be permanent
magnets which can be physically removed or moved away from the
magnetizing station when flushing out the magnetically-separated
target cells. Alternatively, these magnets 18 may be electromagnets
electrically energized via connectors 19 (FIG. 2) during the
magnetic-separation phase, and electrically deenergized during the
flushing-out phase.
[0030] It will be seen that the buffer liquid supplied from the
buffer container 11 provides a constant and continuous fluid
volume, and thereby forms a continuous liquid carrier for all the
constituents of the sample mixture supplied from the sample
container 10. This is true both during the initial depletion stage,
wherein the original sample depleted of the target cells is
received within container 14, and also during the positive
selection stage, wherein the target cells separated and retained in
the magnetizing station 13 are flushed out by the buffer liquid
into another receiving container. The buffer liquid thus
continuously supports both the target cells and the non-targetted
cells during both phases of the separation process such as to
substantially decrease the possibility of damage or rupture of the
cell membranes, as compared to the conventional MiniMACS process
described above. In addition, and as will be further described
below, -the method illustrated in FIG. 1 is highly susceptible to
automation to provide greater through-put capabilities and improved
efficiency in the separation process.
[0031] Following is one example of using the apparatus and method
described above with respect to FIG. 1 for magnetically separating
selected target cells from a blood sample:
[0032] A mixed lymphocyte sample was obtained from a quantity of
normal, healthy blood using a normal ficoll gradient. This sample
was split into two groups: control and experimental.
Commercially-available CD19 magnetic Microbeads (supplied by
Miltenyi Biqtec GmbH) were added to the experimental lymphocytes
for the purpose of tagging only B cells in the sample. After
staining with the CD19 microbeads, the cells were rinsed twice with
PBS.
[0033] The separation device was prepared by filling and rinsing
the feed tube 12 with degassed buffer from the buffer reservoir.
Throughout the separation, the system remains filled with the
degassed buffer.
[0034] The stained lymphocyte mixture was introduced into the
system by way of a 1 ml. syringe (w/o the plunger) with a
0.4.times.13 needle inserted into a "piggyback site" in the tubing.
The vacuum system maintained a steady flow rate of 6 drops per
minute. After all the stained mixture had entered the system, the
needle was removed and the system left to run until an additional
400 .mu.l of buffer had flowed through the separation system. Flow
was halted. The receiving tube was removed, labeled "A", and
replaced with a second tube.
[0035] The magnetic field was discontinued; flow was restored; and
the line was flushed with 500 .mu.l of buffer liquid. Flow was
again halted, and this second tube was removed and labeled "B".
[0036] Cells from the control group and tubes "A" and "B" were
examined in a double blind condition with a light microscope for
membrane condition and cell counts using a hemocytometer.
[0037] There was no change in cell quality between the control and
the experimental samples. Normally, B cells comprise 8-11% of the
total lymphocyte population. Results of this separation yielded
8.8% B cells, Demonstrating the ability to isolate a specific
population with no change in the cell quality.
[0038] Utilizing CD19 microbeads (Miltenyi Biotec GmbH) to stain
for B Lymphocytes, would be expected to produce a harvest of
approximately 10% from the total lymphocyte population. The actual
results, as examined by light microscope, CellScan, and FACS, were
as follows:
[0039] 1. A harvest was produced ranging from 8.8% to 11.1%. FACS
analysis of these cells revealed a 97% pure population of desired
cells.
[0040] 2 The membrane quality was unaffected by the process. This
was verified by both light microscope and CellScan examination.
[0041] 3. The non-stained lymphocyte populations (non-targetted
cells) were expected to contain approximately 95% T Lymphocytes and
comprise approximately 90% of the total lymphocyte population. FACE
analysis of these cells revealed an average of 93% pure T
Lymphocyte populations. Microscopic examination confirmed that
these T Lymphocytes comprised an average of 90% of the total
lymphocyte population.
[0042] In the above-described example, the magnetic field was
produced by permanent magnets of neodymium; the tubing was 0.80 mm
infusion tubing; and the buffer liquid was of the following
composition:
1 0.15 ml EDTA (Ethylenediarnine tetraacetic acid); 1.10 ml BSA 796
(Bovine serum albumin); 13.75 ml PBS (Phosphate Buffered Saline w/o
caclium and magnesium); yielding 15.00 ml total buffer
[0043] FIG. 2 schematically illustrates the basic system of FIG. 1
but equipped with the main controls for automating the operation of
the system.
[0044] Thus, the system illustrated in FIG. 2 includes a
microprocessor controller, generally designated 20, for controlling
the overall operation of the system. The inputs to controller 20
include a flow selector 21 for presetting the flow rate of feed of
the buffer liquid from the buffer container 11; an air bubble
sensor 22 for sensing the presence of air bubbles in the buffer
feed tube 12; and an air bubble sensor 23 for sensing the presence
of air bubbles in the sample feed tube 17. These sensors protect
the integrity of the constant fluid level by shutting down fluid
flow (sensor 22 will close valve 27, and sensor 23 will close valve
28) if an air bubble is detected. Controller 20 also includes an
input from a flow rate sensor 29 for sensing the flow into
container 14.
[0045] Controller 20 in turn controls the electromagnets 18 at the
magnetizing station 13 via line 24 connected to their connectors
19, the vacuum source 16 via line 25 and/or a vacuum valve 26, the
feed rate of the buffer liquid via valve 27 in the feed line 12,
and the feed rate of the sample via valve 28 in the sample line
17.
[0046] FIGS. 3-6 illustrate a variation in the construction of the
magnetic unit in the magnetizing station 13 to enable the
magnetizing station to occupy a substantially longer flowpath of
the buffer liquid carrying the sample, and thereby to increase the
throughput and/or efficiency of the overall separation process.
Thus, whereas in the apparatus illustrated in FIGS. 1 and 2, the
magnetizing station 13 occupies a straight length of the feed tube
12, in FIG. 3 the magnetizing station, therein designated 30, is
constructed to occupy an elongated, serpentine length of the feed
tube 12.
[0047] As shown particularly in FIG. 4, the magnetizing station 30
includes a back mounting plate 31 and a front mounting plate 32
assembled together by pins 32a in plate 32 received with a friction
fit in apertured posts 31a in plate 31. The front mounting plate 31
mounts a plurality of permanent magnets 33 each carried by a
magnetizable core element 34; and similarly, the back mounting
plate 32 mounts a plurality of permanent magnets 35 each carried by
a magnetizable core element 36.
[0048] The permanent magnets 33 and 35 are aligned with each other,
and the magnetizable core elements 34 and 36 are aligned with each
other, so that they define two closed magnetic circuits, one
including air gaps AG.sub.1, AG.sub.2, and the other including air
gaps AG.sub.1, AG.sub.3. The feed tube 12 passes through all three
air gaps AG.sub.1-AG.sub.3, such that the magnetic field produced
by the permanent magnets is effective over a substantial length of
the feed tube.
[0049] The back mounting plate 31 is movably mounted by a pair of
rocker arms 37, 38. Each rocker arm includes a pivotal mounting
37a, 38a to the back mounting plate 31, and another pivotal
mounting 37b, 38b to a collar 39, 40 slidably received on pins 41,
42 projecting from a supporting surface 42. Collar 39 is slideably
received on the upper pin 41, and collar 40 is slideably received
on the lower pin 42 fixed to the supporting surface 43 below pin
41. The two collars 39, 40 are biassed outwardly by coiled springs
44, 45 on their respective pins 41, 43.
[0050] As shown in FIG. 5, the back plate 31 includes three
apertured posts 31a at the upper end, and three such posts at the
lower end in staggered relationship with respect to the posts at
the upper end. The pins 32a in the front mounting plate 32 are
correspondingly arranged so as to be received within the apertured
posts 31a in plate 31. Thus, when the front plate 32 is removed,
the feed tube 12 may be wound around the upper and lower posts 31a
of the back plate 31 in a serpentine fashion (FIG. 5), to produce
downwardly-extending and upwardly-extending stretches 12a-g. The
last downwardly-extending stretch 12g is connected to the receiving
container 14 in FIG. 3.
[0051] As shown in FIG. 6, there is one magnet 33, for each stretch
12a-12g of the feed tube. Since the illustrated example shows seven
such stretches, FIG. 6 illustrates seven such magnets 33 and their
respective core elements 34. There would be a corresponding number
of magnets 35 and core elements 36 carried by the front plate 32,
with the magnets 35 of the front plate aligned with the magnets 33
of the back plate. As noted above, each pair of magnets and core
elements define three air gaps (AG.sub.1-AG.sub.3, FIG. 4) for each
stretch 12a-12g of the feed tube, such that the magnetic field in
the magnetizing station is effective over a considerable length of
the feed tube.
[0052] Pins 32a of the front plate 32, of the same number and
arrangement as the posts 32a so as to be received within those
posts when applying the front plate 35 to the back plate 31, are
dimensioned to produce a friction fit when the pins are received
within the posts. Posts 31 are also dimensioned to define a space,
shown at 46 (FIG. 4), between the magnets 33, 35 carried by the two
plates 31, 32 for receiving the respective stretch 12a-12g of the
feed tube 12.
[0053] After the feed tube has been applied in serpentine fashion
over the apertured posts 31a in the back plate 31, the front plate
32 is applied by inserting the pins 32a through the posts 31a. When
the pins 32a are received within the posts 31a, the pins engage the
collars 39, 40, moving them towards the fixed surface 43 against
springs 44, 45. The back plate 31 is thus moved by rocker arms 37,
38 towards the front plate 37, to thereby firmly sandwich the
respective stretches of the feed tube 12 between the two groups of
magnets 33, 35.
[0054] FIG. 7 illustrates an apparatus similar to that of FIG. 3,
except that the apparatus of FIG. 7 further includes a mixing
chamber 100 at the input port 112a of the feed tube 112 for
pre-mixing the sample mixture applied via inlet tube 110, and the
buffer liquid applied via inlet 111, before being fed, via tube
112, to the magnetizing station 130. The apparatus in FIG. 7
further includes a pump 132, such as a peristaltic pump, in the
outlet end of tube 112 for controlling the feeding of the liquid
therefrom into the receiving container (14, FIG. 3).
[0055] In all the above-described embodiments, the magnetic field
can be controlled according to the particular application to
produce a predetermined field intensity. For this purpose, the
magnetic air gap can be changed when using permanent magnets: and
when using electromagnets, the current can be varied, e.g., via
microprocessor 20 in FIG. 2.
[0056] While the invention has been described above with respect to
selected target cells from a blood sample, it will be appreciated
that the invention could be used in many other applications for the
selection of other target particles from a body, such as selected
proteins, or other types of particles. Also, while the use of
magnetic microbeads is preferred, it will be appreciated that other
magnetic particles may be used in the process. Further, other
sensors, such as for radioactivity, conductivity, etc. can be
included. Many other variations, modifications and applications of
the invention will be apparent.
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