Abstract:
Magnetically labeled cells in a flow chamber cytometer are detected by a GMR sensor. The flow chamber includes a cell guiding device having at least one first and one second magnetic or magnetizable flow strip. The flow strips, which serve to guide the flowing cells across the sensor in a target-oriented manner, are mounted at a distance from each other such that a magnetic field B F  is produced between them. The GMR sensor is arranged in the region of the magnetic field B F  between the flow strips such that the magnetic field B F  can be used as the operating magnetic field B GMR  of the GMR sensor. In this way, the need for additional magnets for operating the GMR sensor is eliminated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application No. PCT/EP2010/061944, filed Aug. 17, 2010 and claims the benefit thereof. The International Application claims the benefit of German Application No. 102009047793.4 filed on Sep. 30, 2009. Both applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    Described below is a flow chamber with a cell guiding device and a GMR sensor for detecting magnetically-labeled cells. 
         [0003]    In a magnetic flow cytometer, labeled cells can be detected with the help of special sensors. For this purpose, a medium which has both unlabeled and also labeled cells is fed through a micro-fluid duct in a flow chamber, on the inner surface of which is positioned the sensor. The labeled cells, in particular, ideally pass very close to the surface of the sensor and are detected by the latter. 
         [0004]    For this purpose use is made, for example, of GMR (giant magneto-resistance) sensors. As is known, the way in which a GMR sensor functions is based on the GMR effect, in which variations in an external magnetic field produce comparatively large changes in the electrical resistance of the sensor or the GMR structure which it contains. In other words, from a measurement of the electrical resistance of the GMR sensor it is possible to reach conclusions about the magnetic field in whose region of influence the GMR is located. 
         [0005]    In typical applications of GMR sensors, an external operational magnet field B GMR  is first created selectively. As soon as a magnetic body comes within range of the GMR sensor in this operational magnetic field B GMR , or moves through the field, the magnetic field changes at the site of the sensor with the consequence that the electrical resistance of the sensor also changes measurably. I.e. with the help of the GMR sensor it is possible to detect or register the presence of the magnetic body. 
         [0006]    In the situation where such a GMR sensor is used in a flow chamber of a flow cytometer, magnetically labeled cells can be detected using the sensor, whereby the measurement principle is based on the effect described above: a magnetically-labeled cell which is passing the GMR sensor affects the operational magnetic field B GMR  at the site of the sensor, so that the presence of the cell can be demonstrated via a measurement of the electrical resistance of the sensor. However, a basic prerequisite which is necessary for the functioning of the GMR sensor is the presence of the external operational magnetic field B GMR . Associated with this is the need to provide an appropriate magnet, for example a permanent magnet or a current-carrying coil. However, this is disadvantageous due to the limited space available, for example, and in the case of a current-carrying coil due to the required circuitry and power supply for the coil. 
       SUMMARY 
       [0007]    It is therefore desirable to make possible low cost cell detection using a GMR sensor. 
         [0008]    A flow chamber, through which a medium having magnetically-labeled cells can flow, has at least one GMR sensor, positioned on an inner surface of the flow chamber, for the detection of cells, together with a cell guiding device with at least one first and one second magnetic or magnetizable flow strip. The flow strips are arranged at such a distance apart that a magnetic field B F  is created between them. The GMR sensor is arranged in the region of the magnetic field B F  between the flow strips in such a way that the magnetic field B F  from the flow strips can be used as the operational magnetic field B GMR  of the GMR sensor. 
         [0009]    It is accordingly possible in an advantageous way to dispense with any additional magnet for operating the GMR sensor. 
         [0010]    In an advantageous embodiment of the flow chamber, the first flow strip is positioned upstream of the sensor, when looking in the forward direction of flow, and is arranged and constructed in such a way that it guides over the GMR sensor the magnetically-labeled cells which are flowing in the forward flow direction. 
         [0011]    In another advantageous embodiment of the flow chamber, the second flow strip is positioned downstream of the GMR sensor, when looking in the forward direction of flow, and is arranged and constructed in such a way that it guides over the GMR sensor the magnetically-labeled cells which are flowing in the backflow direction. 
         [0012]    These embodiments ensure that the majority of the magnetically-labeled cells can actually be detected by the GMR sensor. 
         [0013]    In the method described below for operating a GMR sensor for cell detection in a flow chamber of a flow cytometer, through which flows a medium with magnetically-labeled cells and which has a cell guiding device with at least one first and one second magnetic or magnetizable flow strip, the flow strips are arranged at such a distance apart that a magnetic field B F  is created between them. The GMR sensor is arranged in the region of the magnetic field B F  between the flow strips. The magnetic field B F  between the flow strips can then be used as the operational magnetic field B GMR  of the GMR sensor. 
         [0014]    In a development of the method, the first flow strip guides over the GMR sensor magnetically-labeled cells which are flowing in the forward flow direction. 
         [0015]    In another development of the method, the second flow strip guides over the GMR sensor magnetically-labeled cells which are flowing in the backflow direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiment, taken in conjunction with the accompanying drawings of which: 
           [0017]      FIG. 1  is a cross-sectional view of flow chamber, 
           [0018]      FIG. 2  is a plan view of a micro-fluid duct in the flow chamber, 
           [0019]      FIG. 3  is a side view of a cell guiding device in a GMR sensor, 
           [0020]      FIG. 4  is a plan view of a micro-fluid duct in another embodiment of the flow chamber. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    In these figures, areas, components, assemblies, etc. which are respectively identical or correspond to each other are labeled with the same reference numbers. 
         [0022]      FIG. 1  shows a cross-sectional view of a flow chamber  10  of a flow cytometer. A medium  70 , which contains the magnetically-labeled cells  20  which are to be detected together with unlabeled cells  30 , passes in the direction of forward flow  130  through an opening  40  into the flow chamber  10 . The medium  70  flows through a micro-fluid duct  11  in the chamber  10  and, after the detection, leaves this again through another opening  50 . The magnetically-labeled cells  20  are detected with the help of a GMR sensor  60 . When the magnetic cells  20  pass the GMR sensor  60 , they influence the operational magnetic field B GMR  prevailing at the site of the sensor. This is registered by the GMR sensor  60  and used for the purpose of detection. 
         [0023]    The flow chamber  10  has a cell guiding device  120 . The purpose of this device  120  is to enable the magnetically-labeled cells  20 , which at the entrance  40  to the flow chamber  10  are still randomly distributed in the medium  70 , to be guided selectively over the sensor  60 , i.e. at least within its range, ideally centrally and immediately above the surface of the sensor  60 . A consequence of this is that a significantly greater number of cells  20  can be detected, because significantly fewer cells flow, for example, past the side of the sensor  60 . It is then no longer a matter of chance whether a labeled cell  20  comes within range of the sensor  60  and can be detected. Various forms of embodiment of such a cell guiding device are described in the parallel German patent application “Durchflusskammer mit Zellleiteinrichtung” [Flow chamber with cell guiding device]. 
         [0024]      FIG. 2  shows a plan view of the interior of a flow chamber  10 , where for the sake of clarity the unlabeled cells  30  are not shown. For the same reason, only a few of the cells  20  have, by way of example, been given reference marks. In this exemplary embodiment, the cell guiding device  120  has two flow strips  121 ,  122  where, looking in the direction of forward flow  130 , the first flow strip  121  is arranged in front of the GMR sensor  60  and the second flow strip  122  behind the sensor  60 , so that the first flow strip  121 , the GMR sensor  60  and the second flow strip  122  lie on a line. Thus, after detection, the cells  20  which pass the sensor  60  are also guided on intended paths. The flow strips  121 ,  122  are aligned in the direction of forward flow  130  of the medium. 
         [0025]    The interaction between the magnetic cells  20  and the magnetic flow strips  121  has the effect that, as they flow past the strip  121  in the medium  70 , the cells  20  lose their random distribution and in time arrange themselves over the strip  121 . At its entry end, the first flow strip  121  has a wider region  121 / 1 , with the help of which the labeled cells  121  are guided towards the narrower region  121 / 2  (the term “wide” here refers to the direction perpendicular to the direction of flow  130 , i.e. to the y-direction). In the extreme case, the width of the strip  121  in the region  121 / 1  can correspond to the width of the micro-fluid duct  11 . The width of the flow strip  121  in the narrower region  121 / 2 , at its rear when looking in the forward direction of flow  130 , can essentially be determined by the diameter of the cells  20 , but in general is less than the width of the sensor  60 . The shape of the flow strip shown here is to be understood as merely an example. Other shapes are of course also conceivable, depending on the desired effect. 
         [0026]    With the help of the cell guiding device  120 , the labeled cells  20  which are ordered on the first flow strip  121  are guided selectively over the GMR sensor  60 . Apart from a few exceptions, which have not been captured by the magnetic flow strips  121  and hence are not guided to the sensors  60 , it may be assumed that a majority of the labeled cells  20  in the medium  70  come within range of the GMR sensors  60 , so that with the arrangement shown a high yield can be achieved which manifests itself, for example, in a shorter measurement time for constant statistics, or in improved statistics for a constant measurement time. 
         [0027]    The flow strips  121 ,  122  may be formed of a magnetic or magnetizable material, for example of nickel. As already noted for the first flow strip  121 , the width of the second flow strip  122  can also essentially be determined by the diameter of the cells  20 , but as a rule is less than the width of the sensor  60 . Typically, the strips  121 ,  122  are up to 10 μm wide and 100-500 nm high (z-direction). Heights of the order of magnitude of 1 μm are also conceivable. The micro-fluid duct  11  is typically 100-400 μm wide, 100 μm high and about 1 mm long (x-direction). The GMR sensors  60  are about 25-30 μm wide. 
         [0028]    As a result, it is possible to dispense with any additional magnet for creating the operational magnetic field B GMR  which is necessary for operating the GMR sensors  60 , because the arrangement of the flow strips relative to the GMR sensor  60  results in a magnetic field B F , which can be used as the operational magnetic field B GMR , being created by the magnetic flow strips  121 ,  122 . This is shown in  FIG. 3 . 
         [0029]      FIG. 3  shows a side view or cross-section through the first flow strip  121 , the GMR sensor  60  and the second flow strip  122 . 
         [0030]      FIG. 3A  shows the situation at a first point in time t 1 , at which the magnetically-labeled cell  20  is still so far away from the GMR sensor  60  that the magnetic field B F  created by the two flow strips  121 ,  122  which surround the sensor  60 , the field lines of which point in the example from the first flow strip  121  to the second  122 , is not affected by the cell  20 . 
         [0031]    At a point in time t 2 , which is shown in  FIG. 3B , the magnetically-labeled cell  20  has reached the GMR sensor  60 . The magnetic field B F , which is created by the flow strips  121 ,  122  in the region of the sensor  60 , is altered by the cell  20 , so that the GMR sensor  60  can detect the cell  20  due to the GMR effect described in the introduction. At the site of the GMR sensor  60 , a high field difference is produced between the ends of the magnetic strips  121 ,  122  and due to the magnetically-labeled cell  20  quasi short-circuiting the flow strips  121 ,  122 . The consequence is a large usable step signal, even though no additional magnet is being used for the creation of the external magnetic field B. 
         [0032]    Finally,  FIG. 3C  shows a third point in time t 3 , at which the cells  20  have now left the GMR sensor  60  again. The magnetic field B F  between the flow strips  121 ,  122  has readjusted itself to how it was shown in  FIG. 3A . 
         [0033]    Hence, the magnetic field B F , which is in any case present at the gap between the first and second flow strips  121 ,  122  of the cell guiding device  120 , is used to provide the operational magnetic field B GMR  required for the operation of the GMR sensor  60 , i.e. B GMR =B F . This magnetic field is distorted during the presence of a magnetically-labeled cell  20 , with the effect that the electrical resistance of the GMR sensor  60  changes measurably. 
         [0034]    It is of course conceivable in principle to provide not merely one single track, as shown in  FIG. 2 , formed by the first and second flow strips  121 ,  122  and the sensor  60 , but rather a plurality of such tracks together with an appropriate number of sensors, which will then ideally be arranged parallel to each other. For each track, a magnetic field B F  forms in each case between the first and second flow strips which are arranged respectively before and after the GMR sensor concerned, and this can be used as described above as the operational magnetic field B GMR  of the associated GMR sensor. A corresponding flow chamber is shown in  FIG. 4 . 
         [0035]    In the method of operating the flow chamber, for the purpose of detecting the magnetically-labeled cells  20  in the medium  70  which is flowing through the flow chamber  10  of the flow cytometer, using the GMR sensor  60 , the labeled cells  20  in the flow are, as already indicated above, guided over the GMR sensor  60  by the first magnetic or magnetizable flow strip  121  of the cell guiding device  120 . The second flow strip  122  is advantageously used, for example, when the medium  70  and with it the magnetically-labeled cells  20  are guided over the sensor  60  not only in the forward flow direction  130  (positive x-direction), but alternately in the forward flow direction  130  and in the backflow direction  130 ′ (negative x-direction, cf.  FIG. 2 ). The cells  20  accordingly brush repeatedly over the sensors  60 . This can be used, for example, to improve the statistics. 
         [0036]    The cells  20  passing the sensor  60  are in general already ordered, i.e. no longer randomly distributed. The second flow strip  122  thus serves essentially to guide the cells  20  over the sensor  60 , whereas the first flow strip  121 , in particular its wider region  121 / 1  has in addition the function of collecting the cells  20 , which are initially randomly distributed, and guiding them onto the narrower region  121 / 2 . 
         [0037]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).