WO2009047714A1

WO2009047714A1 - Magnetic manipulation device for magnetic beads

Info

Publication number: WO2009047714A1
Application number: PCT/IB2008/054119
Authority: WO
Inventors: Albert H. J. Immink; Jeroen H. Nieuwenhuis
Original assignee: Koninklijke Philips Electronics N. V.
Priority date: 2007-10-11
Filing date: 2008-10-08
Publication date: 2009-04-16

Abstract

The invention relates to a magnetic manipulation device (110) that can for example be integrated into a magnetic biosensor (100). The magnetic manipulation device (110) comprises at least one core structure (111) with an array of fingers (113) carrying coils (114) which can selectively be supplied with excitation currents by a controller (115). The core structure (111) has preferably a comb-like form and may for example extend along channels (12) of an exchangeable microfluidic device (10) in which a sample with magnetic target particles can be provided. The controller (115) is preferably adapted to generate moving activity patterns.

Description

Magnetic manipulation device for magnetic beads

The invention relates to a magnetic manipulation device and an examination device comprising the former for generating magnetic fields in a manipulation region. Moreover, it relates to the use of such devices.

The US 7 217 561 B2 discloses a device for generating magnetic fields with which magnetic beads can be moved in a sample. The device comprises two conductive structures running parallel to each other, wherein the current density and thus the induced magnetic field varies periodically along the structures. Moreover, a two- dimensional matrix of individual coils for generating magnetic field gradients was disclosed in literature (R. Heer et al., "Acceleration of incubation processes in DNA bio chips by magnetic particles", Journal of Magnetism and Magnetic Materials 311, 244- 248 (2007)).

Based on this situation it was an object of the present invention to provide alternative means for generating magnetic fields inside a sample, particularly magnetic gradient fields that can be used to move magnetic particles, wherein it is desirable that these means are cost-effective and can readily be combined with biosensors.

This object is achieved by a magnetic manipulation device according to claim 1, by an examination device according to claim 2, and by a use according to claim 13. Preferred embodiments are disclosed in the dependent claims.

According to its first aspect, the invention relates to a magnetic manipulation device for generating magnetic fields, particularly magnetic fields that comprise nonzero gradients, in a spatial region that will be called "manipulation region" the following. The generated magnetic fields may serve for different purposes, for example for the active movement of target particles like biological molecules labeled with magnetic beads. The manipulation device comprises the following components: a) At least one (geometrically connected) "core structure" or "core body" that comprises a magnetizable material and an array of pin- like structures that will be called "fingers" in the following and that extend towards the manipulation region. Typical numbers of fingers range from three to 50, preferably from 5 to 20. The term "array" shall denote here in the most general sense any one-, two- or three-dimensional arrangement of objects. In most cases, the array will be a one- or two-dimensional arrangement. b) A plurality of coils (i.e. electrical conductor lines wound to a helix with at least one turn) which are arranged at the fingers of the core structure.

Typically, just one such coil is disposed around each finger of the core structure. c) A controller for selectively supplying excitation currents to the aforementioned coils. The controller may comprise dedicated electronic hardware, e.g. driver circuits with current sources for generating the excitation currents, and/or digital data processing hardware with associated software for executing a higher-level control of the current supply to the coils.

It should be noted that the selectivity of the current supply to the coils shall mean that at least two coils get different currents, e.g. some basic current with different phases. Preferably, the controller is able to supply each coil with an individual excitation current.

The magnetic manipulation device has the advantage to provide strong magnetic fields in a large region in space with a comparatively compact structure and with coils of moderate size. This is achieved by arranging a plurality of selectively controllable coils at the fingers of a connected core structure, wherein said core structure spreads the generated magnetic fields beyond the immediate vicinity of the individual coils.

The invention further relates to an examination device for manipulating a sample in a sample chamber, wherein the term "manipulation" shall denote any interaction with said sample, for example measuring characteristic quantities of the sample, investigating its properties, processing it mechanically or chemically or the like. The examination device is characterized in that it comprises a magnetic manipulation device of the kind described above, i.e. a device for generating magnetic fields in a manipulation region with at least one core structure comprising a magnetizable material and an array of fingers with coils, and with a controller for selectively supplying the coils with excitation currents. The examination device may optionally comprise a seat (i.e. a void space or reservoir) for taking up an exchangeable microfluidic device. The microfluidic device that comes into contact with a sample to be manipulated can thus be handled separately from the examination device and can be designed as a disposable part. In biosensor applications, the microfluidic device may for example be a cartridge or a well-plate to which a biological specimen (e.g. blood, saliva) is applied and which can be inserted into a reader for the execution of the desired biosensor operations.

In many applications, the examination device will comprise at least one sensor element for sensing a characteristic property of a sample and/or a temperature- regulator for controlling the temperature of a sample (i.e. for heating and/or cooling). In a sensor device, the magnetic manipulation device can favorably be applied to affect the distribution of magnetic target particles in a sample, e.g. by attracting them towards a sensitive surface and/or by washing away unbound target particles from a binding surface. The mentioned sensor element may preferably be an optical, magnetic, mechanical, acoustic, thermal and/or electrical sensor element. A magnetic sensor element may particularly comprise a coil, Hall sensor, planar Hall sensor, flux gate sensor, SQUID (Superconducting Quantum Interference Device), magnetic resonance sensor, magneto -restrictive sensor, or magneto -resistive sensor of the kind described in the WO 2005/010543 Al or WO 2005/010542 A2, especially a GMR (Giant Magneto Resistance), a TMR (Tunnel Magneto Resistance), or an AMR (Anisotropic Magneto Resistance). An optical sensor element may particularly be adapted to detect variations in an output light beam that arise from a frustrated total internal reflection due to target particles at a sensing surface. Other optical, mechanical, acoustic, and thermal sensor concepts are described in the WO 93/22678, which is incorporated into the present text by reference. In the following, various further developments of the invention will be described that relate both to the magnetic manipulation device and the examination device.

Thus the magnetizable material of the core structure may optionally comprise a soft magnetic material, particularly iron alloys (e.g. CoFe) and/or ferrites. In general, preferred characteristics of the core material are: high permeability, high saturation magnetization, and a low remanence.

The core structure may preferably have a comb-like form with fingers extending from a stem or backbone. Thus two neighboring coils will be disposed on an U-shaped piece of the core structure, which allows an optimal concentration of magnetic field lines. It was already mentioned that the array of fingers of the core structure may particularly be two-dimensional. In another embodiment of the invention, the array of fingers of the core structure comprises at least one linear section. Such a linear section can then be used to move magnetic particles in an adjacent sample along a line, e.g. along the extension of a microfluidic channel. The controller of the magnetic manipulation device is preferably adapted for generating activity patterns that move wave-like along the array of coils, wherein the "activity pattern" at a point in time is defined by the excitation currents momentarily applied to the individual coils. In a one-dimensional array of fingers/coils, the moving activity pattern may for example comprise the sequential application of a given excitation current to one coil after the other along the line of coils/fingers. The moving activity pattern can particularly be used to move magnetically attracted material, e.g. magnetic beads, through the manipulation region.

In another embodiment of the invention, two core structures may be disposed on opposite sides of the manipulation region. Thus the manipulation region can be reached by magnetic fields from two sides, allowing the control of larger volumes and reducing the risk that magnetic particles may escape from the reach of a single manipulation device.

In a further development of the aforementioned embodiment, the fingers of the two core structures are interlaced. Thus an optimal coverage of the manipulation region with magnetic fields can be achieved. Moreover, magnetically attracted material can be moved in a desired direction by activating the two core structures in an alternating way.

In general, the manipulation region may lie anywhere in space where the generated magnetic fields are required. Thus the manipulation region may extend freely into the ambience if for example environmental measurements in the ambient atmosphere or in water are intended. In a preferred embodiment, a microfluidic device is arranged in the manipulation region, wherein said device can provide a sample to be manipulated in a definite way.

The aforementioned microfluidic device may optionally comprise different regions where different environmental conditions can be established. It may for example comprise several chambers containing different chemicals (e.g. for lysis, amplification, etc.) and/or with different temperatures.

The invention further relates to the use of the magnetic manipulation device and/or the examination device described above for molecular diagnostics, biological sample analysis, or chemical sample analysis, food analysis, and/or forensic analysis. Molecular diagnostics may for example be accomplished with the help of magnetic beads or fluorescent particles or magnetizable fluorescent particles that are directly or indirectly attached to target molecules.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. These embodiments will be described by way of example with the help of the accompanying drawings in which:

Figure 1 shows schematically a cross section through a sensor device with a magnetic manipulation device having a comb-like core structure;

Figure 2 shows in a similar cross section a modified sensor device with a second comb-like core structure;

Figure 3 shows schematically a top view onto a microfluidic device with a magnetic manipulation device according to the present invention below it.

Like reference numbers or numbers differing by integer multiples of 100 refer in the Figures to identical or similar components.

The invention will in the following (without loss of generality) be described with respect to biological assays that rely on the detection of magnetic particles or beads serving as labels for biomolecules of interest. Suited detectors for such magnetic particles are magneto -resistive biochips or biosensors which have promising properties for bio-molecular diagnostics, in terms of sensitivity, specificity, integration, ease of use, and costs. Examples of such biochips are described in the WO 2003/054566, WO 2003/054523, WO 2005/010542 A2, WO 2005/010543 Al, and WO 2005/038911 Al, which are incorporated into the present application by reference. Magnetic labels in biological assays offer several advantages for use in point-of-care diagnostics tests, as they are:

Fast: The magnetic beads can be homogeneously dispersed in a sample. This shortens the incubation time (not dependant on diffusion kinetics anymore). By actuating the beads and attracting them to the sensor surface an upconcentration of target molecules (bound to magnetic labels) takes place. This speeds up the binding to the detector surface.

Reliable: Once beads are attracted towards the sensor surface a bound-free separation needs to take place. Conventionally this is done by fluidic washing which is generally cause of variations in the outcome of the assay. By applying accurate forces via magnetic field gradients a reliable result can be obtained.

Easy to use: The use of magnetic beads allows manipulation with the magnetic labels (by applying proper actuation fields) in order to eliminate conventional steps in the assay procedure, e.g. fluidic washing. This significantly simplifies the fluid cartridge that is used in a bioassay for providing a sample.

Another example in which magnetic manipulation is favorable is bead transport between reaction chambers. For example in a point-of-care DNA-testing cartridge several steps are needed in the complete protocol. Typically these steps are:

Lysis: To break the cells and to access the DNA. - Amplification: To increase the DNA concentration in the sample

(e.g. PCR (Polymerase Chain Reaction) or NASBA (Nucleic Acid Sequence Base Amplification)).

Detection: The final detection step to determine the DNA concentration of a certain type that matches with the complementary oligo that is immobilized on the sensor surface. All these steps may need a different buffer fluid (e.g. a lysis buffer with chemicals to break the cell- wall, an amplification buffer with specific enzymes for the PCR or NASBA protocol, and a detection buffer to optimize hybridization at the sensor surface). One option is to apply pumps and valves and other microfluidic elements to provide a different buffer at different moments during the complete assay protocol. Another solution is to transport the biological molecules of interest by binding them to magnetic beads and move the beads by proper actuation fields from a first buffer solution in a first chamber or region to a second buffer solution in a second chamber or region. Also biological molecules can be moved from a region or chamber with a certain temperature Tl to a region or chamber with another temperature T2 and after a pre- defined time to yet another region or chamber with temperature T3. Such manipulations can for example be needed to perform PCR cycles.

In the scenarios described above, a large actuation structure is needed for moving the beads from one chamber of a microfluidic cartridge to another. Generally, magnetic fields and magnetic field gradients decrease rapidly at larger distances from the core material of an electromagnet. This makes single magnets not suitable for actuation over large distances. An alternative are magnetic actuation structures integrated in a fluidics cartridge; however, these structures add cost to the cartridge and typically require many electrical connections. Additionally, integrated structures tend to create large peaks in field gradient, due to their rather small dimensions. This could lead to unwanted non-specific binding events taking place.

To solve the above problems, it is proposed here to apply comb-like structures with a magnetizable material and with coils for generating magnetic fields inside a manipulation region where the fields are desired. Figure 1 shows a first embodiment of a sensor device 100 according to this approach. The sensor device 100 may for example be a biosensor with sensor elements (e.g. GMR sensors, not shown) for detecting magnetic particles in a sample that is provided in a disposable cartridge 10. It comprises a substrate 120 in which a magnetic manipulation device 110 according to the present invention is embedded. Above the substrate 120, the micro fluidic cartridge 10 is disposed in a seat of the sensor device 100. This cartridge 10 has a cover 11 with microfluidic channels and chambers 12 (in which a sample to be investigated can be provided) and a substrate 13 as a bottom. The substrate can be made of any material that does not cause flux guiding of the magnetic fields lines through its material, i.e. it can be an optical substrate made of injection molded polymer, or it can be some interconnect material that allows the integration of GMR chips in the integrated cartridge. The microfluidic cartridge 10 is typically a disposable made from plastics and thus a component separate from the sensor device 100.

The magnetic manipulation device 100 that is embedded into the substrate 120 comprises the following components:

A soft magnetic core structure 111 with a comb-like form having a stem or backbone 112 and a plurality of fingers 113 extending from it towards the microfluidic cartridge 10.

Coils 114 that are wound around the fingers 113. A controller 115 that is connected to the coils 114 for selectively supplying them with excitation currents.

By applying currents to the electro -magnets 114 fringe magnetic fields will be generated between the poles (tips of the fingers) of the comb-structure. In this way a magnetic field gradient is generated from one pole to the other causing beads in the sample chambers 12 above the poles to move over the comb-structure.

In a more generic embodiment an array of magnetic poles can be present with an array of coils (either one-dimensional or two-dimensional). By driving the coils in a predetermined order bead transport in different directions is possible. This allows more freedom in designing different fluidic cartridges (i.e. different chamber and channel geometries) for a generic reader device. Depending on the fluidic cartridge that is used, particular sub-groups of the coils may be activated in this case (typically those below microfluidic channels). In contrast to the embodiment shown in Figure 1, the magnetic manipulation device might also be disposed above the microfluidic cartridge 10. Figure 2 shows a further embodiment of a microelectronic sensor device 200 in which a first core structure 211a with coils is disposed below the microfluidic cartridge 10 in a substrate 220a, and a second core structure 211b with coils is disposed above the microfluidic cartridge 10 in a substrate 220b, wherein the coils of both core structures are coupled to a controller 215. Thus a magnetic manipulation device 210 with two core structures is realized. Moreover, the coils/fingers of the top core structure 211b are shown to fall in between the coils/fingers of the bottom core structure 211a, i.e. the coils/fingers of the devices are interlaced. This helps to increase the efficiency of the transport.

Figure 3 shows a top view onto a typical microfluidic cartridge 10 comprising an inlet 12a and two fluidic chambers 12c, 12e connected via fluidic channels 12b, 12d. Underneath the fluidic channel 12d a comb-like magnetic manipulation device 310 (like that shown in Figures 1 and 2) is present at the moment the fluidic cartridge 10 is inserted into the reader.

By using magnetic manipulation devices of the kind described above two main problems can be solved:

1. The small interaction range of single magnets is overcome by using a comb-like actuation structure where multiple poles are present under channels or measurement chambers. By applying subsequent current pulses with different phases to the electromagnets it is possible to generate a large magnetic force over a long distance.

2. The high cost of integrated actuation structures in a microfluidic cartridge are avoided as the microfluidic device can be substantially non- magnetic, i.e. it can be made of plastic material made in an injection moulding process. Therefore, the cartridge can be simple and cheap. The comb-like actuation structure is present in the reader and will add cost to the reader only. The described mechanisms particularly allow to move magnetic samples along a flow-channel, which can be used to automate a series of pre-treatment steps. Further advantages of this solution are: a large lateral distance can be covered, so transport from one chamber to the other becomes feasible; the magnetic field of the external magnets extends over the full height of the channels; no moving parts; - no large peak-gradients are generated that could lead to nonspecific binding.

While the invention was described above with reference to particular embodiments, various modifications and extensions are possible, for example:

The microelectronic sensor device can comprise any suitable sensor element to detect the presence of particles on or near to a sensor surface, based on any property of the particles, e.g. it can detect via magnetic methods, optical methods (e.g. imaging, fluorescence, chemiluminescence, absorption, scattering, surface plasmon resonance, Raman, etc.), sonic detection (e.g. surface acoustic wave, bulk acoustic wave, cantilever, quartz crystal etc), electrical detection (e.g. conduction, impedance, amperometric, redox cycling), etc.

A magnetic sensor can comprise any suitable sensor element based on the detection of the magnetic properties of the particle on or near to a sensor surface, e.g. a coil, magneto -resistive sensor, magneto -restrictive sensor, Hall sensor, planar Hall sensor, flux gate sensor, SQUID, magnetic resonance sensor, etc.

In addition to molecular assays, also larger moieties can be detected with sensor devices according to the invention, e.g. cells, viruses, or fractions of cells or viruses, tissue extract, etc.

The detection can occur with or without scanning of the sensor element with respect to the sensor surface.

Measurement data can be derived as an end-point measurement, as well as by recording signals kinetically or intermittently.

The particles serving as labels can be detected directly by the sensing method. As well, the particles can be further processed prior to detection. An example of further processing is that materials are added or that the

(bio)chemical or physical properties of the label are modified to facilitate detection.

The device and method can be used with several biochemical assay types, e.g. binding/unbinding assay, sandwich assay, competition assay, displacement assay, enzymatic assay, etc. It is especially suitable for DNA detection because large scale multiplexing is easily possible and different oligos can be spotted via ink-jet printing on the (e.g. optical) substrate.

The device and method are suited for sensor multiplexing (i.e. the parallel use of different sensors and sensor surfaces), label multiplexing (i.e. the parallel use of different types of labels) and chamber multiplexing (i.e. the parallel use of different reaction chambers).

The device and method can be used as rapid, robust, and easy to use point-of-care biosensors for small sample volumes. The reaction chamber can be a disposable item to be used with a compact reader, containing the one or more field generating means and one or more detection means. Also, the device, methods and systems of the present invention can be used in automated high- throughput testing. In this case, the reaction chamber is e.g. a well-plate or cuvette, fitting into an automated instrument.

Finally it is pointed out that in the present application the term

"comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope.

Claims

CLAIMS:

1. A magnetic manipulation device (110-310) for generating magnetic fields in a manipulation region, comprising a) at least one core structure (111, 211a, 211 b) comprising a magnetizable material and an array of fingers (113) directed towards the manipulation region; b) a plurality of coils (114) that are arranged at the fingers of the core structure; c) a controller (115, 215) for selectively supplying excitation currents to the coils.

2. An examination device (100, 200) for manipulating a sample in a sample chamber (12), comprising a magnetic manipulation device (110-310) according to claim 1.

3. The examination device (100, 200) according to claim 2, characterized in that it comprises a seat for an exchangeable micro fluidic device (10).

4. The examination device (100, 200) according to claim 2, characterized in that it comprises at least one optical, magnetic, mechanical, acoustic, thermal or electrical sensor element, particularly a coil, a Hall sensor, a planar Hall sensor, a flux gate sensor, a SQUID, a magnetic resonance sensor, a magneto -restrictive sensor, or magneto -resistive sensor like a GMR, a TMR, or an AMR element, and/or that it comprises a temperature-regulator for controlling the temperature of a sample.

5. The magnetic manipulation device (110-310) according to claim 1 or the examination device (100, 200) according to claim 2, characterized in that the magnetizable material of the core structure comprises a soft magnetic material, particularly iron alloys like CoFe and/or ferrites.

6. The magnetic manipulation device (110-310) according to claim 1 or the examination device (100, 200) according to claim 2, characterized in that the core structure (111, 211a, 21 Ib) has a comb-like form with the fingers (113) extending from a common stem (112).

7. The magnetic manipulation device (110-310) according to claim 1 or the examination device (100, 200) according to claim 2, characterized in that the array of fingers (113) is two-dimensional and/or that it comprises at least one linear section.

8. The magnetic manipulation device (110-310) according to claim 1 or the examination device (100, 200) according to claim 2, characterized in that the controller (115, 215) is adapted to generate an activity pattern that moves along the array of fingers (113).

9. The magnetic manipulation device (210) according to claim 1 or the examination device (200) according to claim 2, characterized in that two core structures (21 Ia, 21 Ib) are disposed on opposite sides of the manipulation region.

10. The magnetic manipulation device (210) or the examination device (200) according to claim 9, characterized in that at least some fingers of the two core structures (21 Ia, 21 Ib) are interlaced.

11. The magnetic manipulation device (110-310) according to claim 1 or the examination device (100, 200) according to claim 2, characterized in that a microfluidic device (10) is arranged in the manipulation region.

12. The magnetic manipulation device (110-310) or the examination device (100, 200) according to claim 11, characterized in that the micro fluidic device (10) comprises different regions where different environmental conditions can be established.

13. Use of the magnetic manipulation device (110-310) or the examination device (100, 200) according to any of the claims 1 to 12 for molecular diagnostics, biological sample analysis, or chemical sample analysis.