Abstract:
The present invention provides a system for analyzing a sample liquid comprising a test tape having a plurality of test elements, a tape transport device which successively transports the test elements to a sample application site while advancing the tape, and a measuring device which scans the test elements loaded with sample liquid at a measuring site. The measuring site is located at a distance from the sample application site in the direction of tape movement. The tape transport is interrupted in order to exactly position a wetted area of the test elements carrying a sample liquid at the measuring site by means of a positioning device that responds to the presence of sample liquid on the test element.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority to EP 05 024 897.0, filed Nov. 15, 2005.  
       BACKGROUND  
       [0002]     The present invention relates to a system for analyzing a sample liquid, in particular, for blood glucose determinations, comprising a test tape having a plurality of test elements that is preferably stored in a tape cassette, a tape transport device which successively transports the test elements to a sample application site while advancing the tape, and a measuring device which scans the test elements loaded with sample liquid at a measuring site, wherein the measuring site is located at a distance from the sample application site in the direction of tape movement. The invention also relates to a method of using a device of the type having a tape cassette including a tape carrying a plurality of test elements.  
         [0003]     WO 2004/056269 describes a test system for body fluids comprising a test tape for providing a plurality of test units that are applied to sections of a support tape in a compact hand-held device. In the case of blood sugar self-monitoring that usually has to be carried out several times daily this should impose the fewest possible handling steps on the affected person. A deflection of the test elements over a deflecting tip which at the same time constitutes the measuring site is provided in order to be able to meter the smallest possible amount of blood. In addition it is also mentioned that a measuring position at a distance from the collecting position allows reading optics or an electrochemical analytical unit to be separately positioned in the instrument.  
         [0004]     U.S. Pat. No. 6,707,554 B1 describes a photometric analytical system for test elements in the form of test strips which are positioned by means of instrument stops. Several point light sources are provided to illuminate different areas of the detection zone on the test strip in order to compensate for tolerances wherein it is then intended to make a selection on the basis of the signals that are obtained.  
       SUMMARY OF THE INVENTION  
       [0005]     Embodiments of the present invention further improve the systems known in the prior art and in particular enable optimization of instrument design and enable a reliable measurement with the smallest possible amounts of sample.  
         [0006]     The present invention is based on the idea of enabling a directed measurement of test elements without the need for mechanical positioning elements. Accordingly, embodiments of the invention provide a positioning device which responds to the presence of sample liquid on the test element that is active at the time and controls the tape transport device in order to interrupt tape transport to position a wetted area of the test elements carrying sample liquid at the measuring site. In this manner, it is possible to provide a larger test area for sample application without requiring the whole area to be covered. Hence, especially for blood sugar measurements, microscopic amounts of blood are sufficient which can be collected in a painless manner while creating additional comfort due to an integrated lancing unit because the site of collection is not displaced by a measuring unit. The construction of the system is simplified and the constructional space is better utilized by the transport positioning and it can be ensured that an accurately targeted detection takes place even with a variable amount of applied sample.  
         [0007]     The positioning device advantageously comprises a control unit coupled to a tape drive for a targeted stop of the tape at the measuring site and is in particular realized by a program routine of a microprocessor. Another improvement is achieved by means of the positioning device having at least one optical detection unit which responds when the wetted area passes through.  
         [0008]     In order to ensure the sample is accurately centered, it is advantageous when the positioning device has two light sources aligned with (directed to) tape passage positions or spots located before and after a zone of the measuring device that detects the useful signal. This can be achieved simply by the positioning device having several light emitting diodes that are imaged or directed consecutively along a path the test tape travels. The diodes produce consecutive light spots on the tape in the direction of tape movement by common collection optics.  
         [0009]     The positioning device advantageously has at least one photosensor for scanning the test elements preferably by reflectometry. In this connection, it is advantageous when the photosensor detects a blank value in an unwetted area of the test field and a target value that is different therefrom in the wetted area.  
         [0010]     In order to meet the high requirements made on the quality of signal detection, it is advantageous when the measuring device has a detector that is separate from the positioning device for detecting the useful signals for the detection of an analyte in the sample liquid.  
         [0011]     The test elements are advantageously formed as flat test fields on the test tape that are preferably in the form of a reagent layer. The test fields can have a reference area for a blank value measurement that is kept free from the sample liquid by a liquid barrier.  
         [0012]     The fine positioning can also be accomplished by the test tape being provided with a tape marking, in particular, with a line scale, marking holes or color marks at least on sections of the tape and by the positioning device having a scanning means, in particular, a light barrier to scan the tape marking while the tape is advanced. The line scale or the marking holes can be introduced by a laser during tape manufacture.  
         [0013]     In order to reduce the required amount of sample, the wetted area of the test elements preferably has a diameter of less than 5 mm, more preferably, of 1 to 2 mm.  
         [0014]     In order to create sufficient free space for the measuring device, it is advantageous when the measuring site is positioned at a distance of 5 mm to 5 cm from the sample application site.  
         [0015]     In another embodiment of the system design, especially for blood sugar measurements, a lancing device is positioned at the sample application site for piercing a body part, preferably through the test tape.  
         [0016]     The tape transport is controlled by a positioning device that responds to the presence of sample liquid on the test element in order to position a wetted area of the test element carrying a sample liquid at the measuring site.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above-mentioned aspects of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0018]      FIG. 1  is a schematic plan view illustrating a test tape system for blood glucose determination;  
         [0019]      FIG. 2  is a diagrammatic view in partial perspective illustrating a positioning device for positioning the test tape at the site of measurement;  
         [0020]      FIG. 3  is a top view illustrating a section of test tape provided with test element;  
         [0021]      FIGS. 4   a  and  4   b  illustrate two diagrammatic side views of the positioning device aligned with the test tape;  
         [0022]      FIGS. 5   a  thru  5   e  illustrate different wettings of a test field with the corresponding reflectance signals; and  
         [0023]      FIGS. 6   a  thru  6   e  illustrate another embodiment of a positioning device illustrating a section of test tape in various positions in its advancement. 
     
    
       [0024]     Corresponding reference characters indicate corresponding parts throughout the several Figures.  
       DETAILED DESCRIPTION  
       [0025]     The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.  
         [0026]     The test system shown in the drawings includes a test tape  12  having a plurality of test elements  14  located thereon which is inserted into a hand-held device  10  as a cassette, a transport device  16  for tape transport, a measuring device  18  for optically analysing the test elements  14  and a positioning device  20  to position the test fields  14  in the detection area of the measuring device  18 .  
         [0027]     As illustrated in  FIGS. 1 and 2 , the test tape  12  can be pulled from a supply spool  22 , pulled over various deflector rollers  24  and a deflector head  26 , and advanced along a path indicated by arrow  28 , i.e., in the direction of tape movement (arrow  28 ), and then wound onto a take-up reel  30 . The tape is advanced (along path  28 ) by a motorized tape drive  32  which engages the take-up reel  30 . Appropriate tape stops can be used to apply body fluid (blood) selectively to the test elements  14  in the area of the deflector head  26  at a sample application site and subsequently to optically scan them inside the instrument at the measuring site  36  by means of the measuring device  18 .  
         [0028]     As shown in  FIG. 3 , the test elements  14  are provided in the form of flat test fields composed of a reagent layer  38  which is applied to a transparent thin support tape  40 . When a drop of blood is applied, the reagent layer  38  reacts to an analyte such as glucose in the sample fluid by producing a change in color, thus enabling an optical detection using the measuring device  18 .  
         [0029]     It is desirable for the user to be required to apply as little blood as possible, yet at the same time have available a large application zone  38 . As a result, the area  42  that is wetted with blood or sample liquid can vary from measurement to measurement, and a positioning device  20  comprising a microprocessor ensures that the wetted area  42  is accurately detected at the measuring site  36  that is distant from the application site  34 . For this purpose, the tape drive  32  is appropriately actuated such that positioning is achieved by interrupting the transport without requiring additional mechanical elements. In addition to the application zone  38 , the test field  14  has a reference area  46  for a blank value measurement that is separated by a hydrophobic liquid barrier  44 .  
         [0030]      FIG. 4  illustrates the fine positioning of the wetted area  42  at the measuring site  36  by means of a photometric positioning device  20 . The side view of  FIG. 4   a  shows three light-emitting diodes  48  that are arranged in succession in the direction of tape movement and are imaged or directed consecutively on the passing tape  12  as corresponding light spots  52  by a collecting lens  50 . In other words, the three diodes  48  are directed to three successive and adjacent spots on the path that the test tape travels. The spacing of the outer LEDs  48  is of the order of magnitude of the usual dimensions of the wetted zone  42 , i.e., in a range of a few millimeters. The view of  FIG. 4   b  in the direction of tape movement shows that the light  54  that is irradiated by the light-emitting diodes  48  and that is diffusely reflected by the test elements  14  on the test tape  12 , is detected laterally outside of the direct reflection by a detector or photosensor  56  of the positioning device  20 . In order to allow an assignment of the signals obtained using only one sensor  56 , the LEDs  48  can be actuated separately from one another. In principle, it is possible that the sensor  56  is also used to detect the useful signal in addition to the presence of the wetted area. However, in order to meet the various requirements it is expedient to use a separate detector for this purpose.  
         [0031]      FIG. 5  shows the spatial correlation of the various output signals of the sensor  56  to the respective wetted states of the test field  14  which are each shown above. When the test field  14  is completely dry, i.e., sample liquid has not been applied to the reaction area  32  and reference area  46 , a blank value L is detected in both areas ( FIG. 5   a ). In the case of the central wetting of the area  38  shown in  FIG. 5   b  a lower reflectance value B is measured there corresponding to a color change in the reaction layer.  FIGS. 5   c  and  5   d  show the situation of a wetting of the margin at the start and end of the reaction area  38 , whereas a wetting of the whole area is shown in  FIG. 5   e.    
         [0032]     It should also be noted that the test tape  12  can be provided with a puncture opening  58  located before the test element  14  for a lancing unit arranged in the area of the sample application site  34 . Thus, with a standardized instrument it is possible by means of the lancing unit to collect capillary blood, for example, from a finger, to pick up blood at the sample application site  34  with a test element  14  by advancing the tapes and subsequently to position the respective test element at the measuring site  36  by advancing the tape further.  
         [0033]     In this connection, the fine positioning can be achieved by means of the described row of light-emitting diodes  48  according to  FIG. 4 . When the reference area  46  passes through the first light spot  52  positioned along path  28  (generated by the right light-emitting diode  48  in  FIG. 4   a ) the blank value L is detected and stored for comparison. When the wetted area  42  arrives at spot  52 , the applied blood is detected by a lowered plateau or target value B of the reflectance which is less than L but larger than zero. When this value rises again, a control unit of the positioning device  20  interrupts the tape drive  32  such that the area  42  wetted with blood is located in the spot of the beam area of the middle LED  48 , which can then also be used to carry out the actual test measurement. In order to further increase the reliability, a third light-emitting diode  48  can be provided (the left LED in  FIG. 4   a ) which, if there is an additional response to blood, ensures that the entire detection area for useful signals illuminated by the middle LED is located in the test field area  42  wetted with blood.  
         [0034]     In the embodiment shown in  FIG. 6  the same parts are labelled with the same reference numerals as described above. A line scale  60  is additionally applied to the test tape  12  at a defined distance from a respective test element  14 . In this case the positioning unit  20  comprises two light barriers  62 ,  64  to scan the test tape  12  as it passes over a housing edge  66  or seal  68 . Blood is collected at the sample application site by lancing unit  70  ( FIG. 6   a ) and subsequently applied to the test field  14  after appropriate tape advancement ( FIG. 6   b ). In the course of further tape advancement, the start of the wetted area  42  is detected by a first light barrier  62  ( FIG. 6   c ). At the same time the respective tape position is determined at the second light barrier  64  the line scale  60 . Optionally, the end position of the wetted area can be determined according to  FIG. 6   d . The required forward movement for an exact positioning of the measuring device  18  is then calculated in the control unit of the positioning device  20  on the basis of the determined tape positions and executed by corresponding further scanning of the scale  60  and control of the tape drive  32  such that an accurate point measurement is possible in the position to which the wetted area has been moved according to  FIG. 6   e.    
         [0035]     In addition to blood, it is also possible to analyze other sample or body fluids, in particular, interstitial fluid, in the manner described above.  
         [0036]     While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.