EP2311564A1

EP2311564A1 - Microfluidic system with chamber and means for generating alternating magnetic fields

Info

Publication number: EP2311564A1
Application number: EP09172166A
Authority: EP
Inventors: Axel Sebastiaan Lexmond; Paul Keijzer
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 2009-10-05
Filing date: 2009-10-05
Publication date: 2011-04-20

Abstract

Microfluidic system comprising a processing chamber (1) and an assembly (2a-b,2a-d) for generating mutually alternating magnetic fields, provided in the vicinity of the processing chamber. Preferably, the assembly comprises a yoke (3) at one location relative to the processing chamber and at least one yoke (3) at another location relative to the processing chamber, each of the yokes comprising at least two yoke legs (4a,4b), connected to an alternatable magnetic field source between them, as well as an open end area including a small gap area (5) between both open yoke leg ends, the small gap areas of the yokes involved being located at different locations relative to the processing chamber, the alternatable magnetic field sources involved being arranged that, alternately, in one period a magnetic field is generated in the small gap area at one location of the processing chamber, and in another period a magnetic field is generated in the small gap area at another location of the processing chamber. The switchable magnetic field source may include a permanent magnet (6) and a rotatable magnet (7), either made of neodymium.

Description

Microfluidic system comprising a processing chamber and an assembly for generating mutually alternating magnetic fields, provided in the vicinity of the processing chamber. The system may be used for separating bound/free fractions employing magnetizable particles (beads), allowing the particle bound substance to be separated by applying a magnetic field.
Separation of bound/free fractions is greatly simplified by employing magnetizable particles (beads), which allow the particle bound substance to be separated by applying a magnetic field. Small magnetizable particles are well known in the art, as is their use in the separations involving immunological and other biospecific affinity reactions. Small magnetizable particles generally fall into two broad categories. The first category includes particles that are permanently magnetized, and the second comprises particles that become magnetic only when subjected to a magnetic field. The latter are referred to as paramagnetic or superparamagnetic particles and are usually preferred over the permanently magnetized particles.
For many applications, the surface of paramagnetic beads is coated with a suitable ligand or receptor, such as antibodies, lectins, oligo nucleotides, or other bioreactive molecules, which can selectively bind a target substance in a mixture with other substances. Examples of small magnetic particles or beads are disclosed in U.S. Pat. Nos. 4230685 , 4554088 , and 4628037 . The use of paramagnetic particles is taught in publications, "Application of Magnetic Beads in Bioassays," by B., Haukanes, and C. Kvam, Bio/Technology, 11 :60-63 (1993); "Removal of Neuroblastoma Cells from Bone Marrow with Monoclonal Antibodies Conjugated to Magnetic Microspheres" by J. G. Treleaven et.al. Lancet, Jan. 14, 1984, pages 70-73; "Depletion of T Lymphocytes from Human Bone Marrow," by F. Vartdal et.al. Transplantation, 43: 366-71 (1987); "Magnetic Monosized Polymer Particles for Fast and Specific Fractionation of Human Mononuclear Cells," by T. Lea et.al., Scandinavian Journal of Immunology, 22: 207-16 (1985); and "Advances in Biomagnetic Separations," (1994), M. Uhlen et.al. eds. Eaton Publishing Co., Natick, Mass.
The magnetic separation process typically involves mixing the sample with paramagnetic particles in a liquid medium to bind the target substance by affinity reaction, and then separating the bound particle/target complex from the sample medium by applying a magnetic field. All magnetic particles except those particles that are colloidal, settle in time. The liquid medium, therefore, must be agitated to some degree to keep the particles suspended for a sufficient period of time to allow the bioaffinity binding reaction to occur. Examples of known agitation methods include shaking, swirling, rocking, rotation, or similar manipulations of a partially filled container.
For a good operation fair refreshment of the liquid outside the beads is crucial. Due to the fact that (natural) mixing hardly occurs in the microfluidic processing chambers and the diffusion rate of many (biological) substances is low, refreshment of the liquid is restricted and collection of the substance (e.g. DNA) will cost much time. Fair mixing could reduce the total processing times from some hours to only some (tens of) seconds, causing the total analysis time to be reduced and the effective capacity to be raised tremendously.
One aim of the present invention to provide a system having improved bead mixing capabilities.
Another aim of the invention is to provide a system providing shortened processing times.
According to the invention a microfluidic system comprises a processing chamber and an assembly for generating mutually alternating magnetic fields, provided in the vicinity of the processing chamber. By applying mutually alternating magnetic fields the beads inside the processing chamber will always be moved towards the location having the highest magnetic field strength
In a preferred embodiment the assembly for generating mutually alternating magnetic fields comprise a yoke at one location relative to the processing chamber and at least one yoke at another location relative to the processing chamber, each of said yokes comprising at least two yoke legs, connected to an alternatable magnetic field source between them, as well as an open end area including a small gap area between both open yoke leg ends, the small gap areas of the yokes involved being located at different locations relative to the processing chamber. Preferably, the alternatable magnetic field sources involved are arranged that, alternately, in one period a magnetic field is generated in the small gap area at one location of the processing chamber, and in another period a magnetic field is generated in the small gap area at another location of the processing chamber, and so on.
The switchable magnetic field source preferably includes a permanent magnet, the magnetic north and south poles being magnetically connected with the yoke legs, which yoke legs, moreover, are magnetically connected with an alternatable magnet, i.e. a magnet which is arranged so that, alternately, in one period its north pole is magnetically connected with a first one of said yoke legs and its south pole is magnetically connected with a second one of said yoke legs, and in another period its north pole is magnetically connected with the second one of said yoke legs and its south pole is magnetically connected with the first one of said yoke legs.
The alternatable magnet may e.g. be constituted by an alternately energizable electromagnet. In a preferred embodiment, however, the alternatable magnet is constituted by a movable, e.g. rotatable, permanent magnet.
Hereinafter the invention will elucidated with reference to some figures:

Figure 1: shows schematically a first embodiment of the system comprising two modules for generating a variable magnetic field, as well as a detailed illustration of the operation;
Figure 2: shows schematically a second embodiment of the system comprising four modules for generating a variable magnetic field;
Figure 3: shows an alternative embodiment for the modules for generating a variable magnetic field;
Figure 4: shows a further alternative embodiment for the modules for generating a variable magnetic field.

In a processing chamber 1 of a microfluidic chip contains magnetizable beads (not shown). The magnetizable property of the beads urges the beads to move always to the area within the processing chamber 1 having the highest magnetic field strength (independent of the direction of the magnetic flied lines). Figure 1 shows an embodiment which comprises a processing chamber 1 and an assembly for generating mutually alternating magnetic fields having gradients in mutually different directions, provided in the vicinity of the processing chamber 1. The assembly, consisting in two (figure 1) or more (figure 2) modules 2a, 2b etc., provides always changing magnetic fields, generated by said modules 2a, 2b, etc., each having a magnetic gradient pointing towards the relevant module 2a, 2b, etc., i.e. the magnetic field strength is always maximum at the side walls of the processing chamber. By subsequent energizing the different modules 2a, 2b, etc. -at different locations- the magnetic beads will be moved through the liquid (or any fluid) surrounding those beads. By this movement of the beads through the liquid the liquid around the beads will be refreshed continuously, meeting the aims of this invention.
The assembly for generating mutually alternating magnetic fields having gradients in mutually different directions, provided in the vicinity of the processing chamber comprises a yoke 3a at one location relative to the processing chamber 1 and at least one yoke 3b at another location relative to the processing chamber 1. Each of the yokes 3 comprises at least two yoke legs 4a, 4b, connected to an alternatable magnetic field source between them, as well as an open end area including a small gap area 5, e.g. having a width of 1 to 5 millimetres, between both open yoke leg ends. The small gap areas 5 of the yokes involved being located at different locations relative to the processing chamber 1. The alternatable magnetic field sources involved are arranged that, alternately, in one period a magnetic field is generated in the small gap area at one location of the processing chamber, and in another period a magnetic field is generated in the small gap area at another location of the processing chamber, thus enabling that the beads will be attracted by the maximum field strength area, always generated by one of the alternately energized modules 2a, 2b, etc.
As explicitly shown in figure 1, the switchable magnetic field source includes a permanent magnet 6, the magnetic north pole N and south pole S being magnetically connected with the yoke legs 4a, 4b. The yoke legs 4a, 4b, moreover, are magnetically connected with an alternatable magnet, i.e. a rotatable magnet 7, which is arranged (i.e. rotatably driven) so that, alternately, its north pole N is magnetically connected with a first one of the yoke legs 4a and its south pole S is magnetically connected with a second one of the yoke legs 4b, causing that both magnets have the same polarity and thus cause a strong magnetic field in the gap area 5. On rotation of the rotatable magnet the resulting magnetic field of each module 2a, 2b, etc. present in the neighbourhood of their gaps 5 thus will fluctuate between the sum of the values generated by each permanent magnet 6 and 7, illustrated in figure 1b, and zero (supposed that both permanent magnets 6 and 7 have equal magnetic force), illustrated in figure 1d. One complete turn of the rotatable magnet 7 has been illustrated in the figures 1b - 1f.
Figure 1a shows an embodiment comprising two switchable (alternatable) magnet modules 2a and 2b, each comprising a yoke 3 including yoke legs 4a and 4b, as well as a fixedly connected magnet 6 and a rotatable magnet 7. Both magnets 7 are rotated during operation, however having their magnet directions mutually shifted over 180°. Due to this, when both magnets 7 are rotated (always having a mutual "phase shift" of 180°) an alternating magnetic field will occur which alternates between (in figure 1a) the upper and the lower magnetic modules 2a, 2b.
In another embodiment, shown in figure 2, four magnetic modules 2a - 2d are provided, each comprising a yoke 3, including a gap 5, a fixedly connected magnet 6 and a rotatable magnet 7. The rotation means (not shown) which are arranged for rotating the magnets 7 may have a mutual "phase shift" of 90°, instead of -as in figure 1a- 180°. The phase distribution, enabled by the magnets rotation (drive) means, may be represented by the sequence 2a - 2b - 2c -2d, indicating that subsequently modules 2a, 2b, 2c, and 2d will have their maximum magnetic force (occurring in their gaps 5) in that sequence 2a - 2b - 2c -2d. However, it may be preferred to chose another sequence, e.g. 2a - 2c - 2b - 2d, which might improve the bead/fluid mixing process within the processing chamber.
Figure 3 shows an alternative embodiment for the modules for generating a variable magnetic field. Similar to the earlier embodiment the switchable magnetic field source includes a permanent magnet 6, the magnetic north (N) and south (S) poles are magnetically connected with the yoke legs 4a and 4b, which are magnetically connected with a switch member 8 which is arranged to, alternately, shortcut both poles of the permanent magnet 6 in one period (left) and to remove said shortcut in another period (right). The rotatable switch member 8 is formed by a body 9 made of a magnetically non-conducting material, e.g. a ceramic or synthetic material, holding a magnetically conducting connection member 10 which magnetically interconnects both yokes 4a and 4b and thus shortcuts the permanent magnet 6 (left) in one period and, in another period (right) removes that magnetic shortcut thus causing an alternating magnetic field in the air gap 5.
Figure 4 shows another alternative embodiment for the modules for generating a variable magnetic field. The switchable magnetic field source includes a permanent magnet 6, the magnetic north (N) and south (S) poles or which are magnetically connected with the yoke legs via a switch member 8 between a magnet pole and yoke leg 4b. The switch member 8, constituted again by magnetic non-conducting body 9 and magnetically conducting connection member 10, is arranged to, alternately, connect the pole of the permanent magnet 6 to yoke leg 4b in one period and to disconnect that pole of the permanent magnet 6 from the yoke leg 4b in another period, thus causing an alternating magnetic field in the air gap 5.

Claims

Microfluidic system comprising a processing chamber (1) and an assembly (2a-b, 2a-d) for generating mutually alternating magnetic fields, provided in the vicinity of the processing chamber.
System according to claim 1, said assembly comprising a yoke (3) at one location relative to the processing chamber and at least one yoke (3) at another location relative to the processing chamber, each of said yokes comprising at least two yoke legs (3a, 3b), connected to an alternatable magnetic field source between them, as well as an open end area including a small gap area (5) between both open yoke leg ends, the small gap areas of the yokes involved being located at different locations relative to the processing chamber, the alternatable magnetic field sources involved being arranged that, alternately, in one period a magnetic field is generated in the small gap area at one location of the processing chamber, and in another period a magnetic field is generated in the small gap area at another location of the processing chamber.
System according to claim 2, wherein the switchable magnetic field source includes a permanent magnet (6), the magnetic north (N) and south (S) poles being magnetically connected with the yoke legs, which yoke legs, moreover, are magnetically connected with an alternatable magnet (7), i.e. a magnet which is arranged so that, alternately, in one period its north pole is magnetically connected with a first one of said yoke legs and its south pole is magnetically connected with a second one of said yoke legs, and in another period its north pole is magnetically connected with the second one of said yoke legs and its south pole is magnetically connected with the first one of said yoke legs.
System according to claim 3, wherein said alternatable magnet is constituted by an alternately energizable electromagnet.
System according to claim 3, wherein said alternatable magnet is constituted by a movable, e.g. rotatable, permanent magnet.
System according to claim 2, wherein the switchable magnetic field source includes a permanent magnet (6), the magnetic north (N) and south (S) poles being magnetically connected with the yoke legs, which yoke legs, moreover, are magnetically connected with a switch member (8) which is arranged to, alternately, shortcut both poles of the permanent magnet (6) in one period and to remove said shortcut in another period.
System according to claim 2, wherein the switchable magnetic field source includes a permanent magnet (6), the magnetic north (N) and south (S) poles being magnetically connected with the yoke legs via a switch member (8) between either magnet pole and yoke leg, which switch member (8) is arranged to, alternately, connect the relevant pole of the permanent magnet (6) to the relevant yoke leg in one period and to disconnect the pole of the permanent magnet (6) from the yoke leg in another period.
System according to any of claims 3 or 5 - 7, wherein either of said magnets is made of neodymium.