Patent Publication Number: US-7910375-B2

Title: Test system for analyzing body fluids

Description:
RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 11/468,049 now U.S. Pat. No. 7,708,948 filed Aug. 29, 2006, which claims priority to EP 05 018 973, filed Sep. 1, 2005. 
    
    
     BACKGROUND 
     The present invention relates to a test system for analyzing body fluids, in particular blood, of the type comprising a test element tape carrying a plurality of test elements that is preferably wound in a tape cassette, a tape deflector for the test element tape for the directed application of body fluid, and a light source as well as a detector to optically analyze test elements to which body fluid has been applied. 
     Portable devices operating as minilaboratories, which can also be used by laymen to carry out the required steps in a simple and rapid manner are known for self-monitoring blood glucose by diabetics. In order to replace conventional test strips, it is proposed in WO 2004/047642 that instead of individual test strips, a wound test tape should be used on which a plurality of test fields provided with a suitable test chemistry are arranged consecutively. The body fluid is applied to a test field that is moved into an active position by advancing the tape over a tip and analyzed. Details on blood collection as well as on the known test media and detection systems especially for blood glucose are disclosed in this document to which reference is herewith made and the contents of which are incorporated by reference into this application. This document also shows that a transparent tip can be used to directly couple the instrument optics. Constraints that have to be observed in this case are that the total height of the deflector tip and its opening angle should be as small as possible but it should still be possible to optically analyze the test field for example on the basis of a reflectance measurement or a fluorescence measurement. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above-noted disadvantages and provides an improved and simplified system of the type mentioned above, and in particular, also reduces strain on the test tape in order to achieve a reliable measurement process in a compact instrument. 
     Exemplary embodiments of the present invention provide a deflector for the test tape which is advantageous for tape transport as well as for optical analysis. In exemplary embodiments, the tape deflector has a rotatable optical element positioned in or along the optical path between the light source and the detector. The optical element rotates to transport the test tape. The optical element, which rotates during tape transport, considerably reduces frictional losses in the tape deflection, thus considerably reducing the risk of tape deformation or of a tear in the tape. This also allows the use of thinner carrier tapes, which in turn, allows a greater quantity of tests to be provided within a given cassette volume. Moreover, the tape can be transported with less motor output and at the same time with less power consumption. The transparent optical element also creates a simple optical access to the test element without the test element having to be transported further to a distant measuring position. 
     The light permeable optical element preferably has a deflector surface that rests against the test element tape and can be rotated in the direction of tape transport to ensure a direct optical coupling in the measuring position and a rotation of the deflector as the tape advances. 
     Another advantageous embodiment provides that the optical element consists of a lens which focuses the light of the light source onto the respective test element to be analyzed on the test element tape. This allows imaging effects to be utilized for a miniaturization of the measuring field. 
     Another constructional improvement is achieved by designing the optical element as a cylindrical lens which is mounted so that it can rotate freely about its longitudinal axis and guides the test element tape on its outer surface. 
     For tape transport, it is favorable when the optical element has a circular, elliptical or polygonal rotationally symmetric cross-section. 
     The optical element can be rotatably mounted in a sleeve bearing, a pivot bearing or conical bearing to provide a simple bearing with sufficiently low friction. 
     Another advantageous embodiment of the optical coupling provides that the optical element in combination with a lens located downstream of the light source and/or upstream of the detector forms the imaging optics. 
     In order to screen the detector from ambient light, it is advantageous when a diaphragm is located in the area of an intermediate image between the test element tape and the detector. 
     According to a further exemplary embodiment, the detector is arranged outside of the area of incidence or of the optical axis of the light specularly (directly) reflected from the test element or of the light beam of the light source. In this manner it is possible to differentiate purely geometrically between the diffusely (in all directions) reflected light which provides the information on the analyte from the reagent layer of the test field, whereas the specular reflection does not reach the entry cross-section of the detector, at least not to a significant extent. 
     Such a geometric separation can be achieved by aligning the light source at an angle of incidence to the test element tape and aligning the detector at a larger detection angle in comparison thereto in a common plane on one side of the axis of incidence. 
     Another advantageous arrangement provides that the light source and the detector are arranged in a common half-space at a lateral distance from a boundary plane spanning the center line of the test element tape in the region of the tape deflector. The light that is reflected normally is essentially radiated into the other half-space without reaching the detector. 
     From a constructional point of view it is particularly advantageous when the light receiver and the detector are arranged on a support in an instrument which receives the tape cassette and are aligned with the tape deflector by means of an optical deflection means and in particular by a mirror integrated in the tape cassette. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a perspective view of a blood sugar measuring instrument with a tape deflector for use of a test element tape; 
         FIG. 2  is a simplified cross-sectional view illustrating the tape deflector provided as a rotatable cylindrical lens in conjunction with a reflectometric measuring device; 
         FIG. 3  shows a longitudinal section through the arrangement of  FIG. 2 ; 
         FIG. 4  shows another embodiment of an optical deflection roller in a view corresponding to  FIG. 3 ; 
         FIG. 5  shows a polygonal deflection roller in profile; 
         FIG. 6  is a perspective view of a cassette part containing the deflection roller for the test element tape; 
         FIG. 7  is a sectional perspective view showing a measuring arrangement of the blood sugar measuring instrument; and 
         FIG. 8  shows a partial sectional side-view of the arrangement of  FIG. 7 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. 
     DETAILED DESCRIPTION 
     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. 
       FIG. 1  shows a test system for body fluids and in particular a blood sugar measuring instrument  10  in the form of a portable hand-held instrument. It includes an instrument housing  12  with a display  14  in which a tape cassette  16  can be inserted as a consumable part. The cassette contains a test element tape  18  which is expediently provided with test elements or test elements  20  spaced apart on sections thereof. Body fluid (blood) can be applied to the test elements  20  in order to quantitatively detect an analyte (glucose) contained therein by means of a reflectometric measurement. 
     The individual test elements  20  are moved successively into a receiving position or testing position in the deflection area in which their front faces are accessible for a selected application of a small amount of body fluid by winding the test tape  18  forwards over a tape deflector  22  that has a basic V-shaped form. The optical measurement takes place from the rear side of the tape through the tape deflector  22  wherein the test element tape can have a transparent carrier foil or a tape cut-out in the area of the test elements  20 . After measurement, the used test element  20  is wound onto a take-up spool of the tape cassette  16  during which an unused test field on the adjoining section of tape is drawn off from a supply spool. In this manner the user can carry out a plurality of tests in an automated measuring process without requiring complicated handling steps. 
     As shown in  FIG. 2 , the tape deflector  22  has a transparent rotatable lens element  24  positioned in the optical path  26  of the optical measuring device  28 . The outer wall  30  of the circularly cylindrical lens element  24  composed of glass or transparent plastic forms a deflection surface which rotates with the test element tape  18  during tape transport so that only slight frictional losses occur. At the same time, the lens element  24  focuses the measuring light generated by the light source  32  of the measuring device  28  onto the test element  20  that is present at that time in the receiving position. In order to improve the light yield, a converging lens can be arranged in front of it. 
       FIG. 3  shows a possible sleeve bearing of the cylindrical lens  24  in the form of front-facing pivot bearings  36  in the side walls  38  of the cassette  16 .  FIG. 3  also shows a possible arrangement of the light source  32  and detector  40  of the measuring device  28  for the detection of the measuring light that is diffusely reflected from the test element  20 . For this purpose, the detector  40  is arranged outside of the optical axis of the light from the light source  32  that is specularly reflected from the facing rearside of the test element  20 . In the embodiment illustrated in  FIG. 3 , the light source  32  and the detector  40  are aligned in one plane which extends through the axis of rotation  42  of the cylindrical lens  24  and the zenithal line  44  of the tape deflector wherein the detector  40  is arranged at a larger receiving angle β compared to the beaming angle α of the light source  32 . 
       FIG. 4  shows another alternative for the simple pivoting of the cylindrical lens  24 . In this example front-facing conical bearings  46  are provided for a low friction point contact. A low positioning tolerance is employed, especially perpendicular to the axis of rotation  42 , as well as low friction and ability to be manufactured economically. 
     As shown in  FIG. 5 , the lens or deflection roller  24  can also have a polygonal geometry instead of a circular cross-section. In the embodiment shown, the basic shape is that of a pentagon in order to thus achieve better defined transport paths for the tape transport. In this case, the side surfaces  48  are rounded or chamfered in order to advantageously design the optical paths. 
     According to  FIG. 6 , the tape cassette  16  can have a cassette tip  50  with V-shaped converging tape guide surfaces  52  where the cylindrical lens  24  is positioned in the apex region. Form-locking structures (not shown) can be provided within the cassette tip  50  for exact alignment when the measuring device  28  is attached where openings in the walls  54 ,  56  allow the light source and detector to be engaged from below. 
     As shown in  FIGS. 7 and 8 , the light source  32 —in the form of three LEDs  58 —and the detector  40  are arranged on an instrument mainboard  60 , whereas the optical light path is determined by elements on the cassette. In detail, these elements are a deflecting mirror  62 , a converging lens  34  and the cylindrical lens  24  as a deflection roller for the test tape  18 . The lens  34  arranged in front has a simple convex lens surface  64  facing the deflection roller and a double convex lens surface  66  facing the measuring device  28  where a central diaphragm  68  between the lens segments separates the light source  32  from the detector  40 . 
     Also in this case the geometric arrangement of the optical elements ensures that only light that is diffusely reflected from the rear side  70  of the test element  20  is detected. For this purpose the light source  32  and the detector  40  are arranged in the half-space below the plane extending through the centre line  74  of the test tape such that the specularly reflected light is essentially radiated into the half-space above it. Calculations made on this configuration show that the proportion of specularly reflected light detected in the detector relative to the total emitted light of the light source is less than 0.001 ppm whereas the ratio of detected to emitted light is about 0.13%. Hence, this ensures that mainly only diffusely reflected light from the reagent layer of the test element  20  is detected. 
     In summary, it may be ascertained that the embodiments disclosed herein concern a test system for analyzing body fluids and in particular blood comprising a test element tape  18  carrying a plurality of test elements  20 , a tape deflector  22  for the test element tape for the selective application of body fluid and a light source  32  as well as a detector  40  for optically analyzing test elements to which body fluid has been applied. The tape deflector  22  has a rotatable optical element  24  as a deflection roller to transport the test element tape  18  in the optical path between the light source  32  and detector  40 . 
     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. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               10  Blood sugar measuring instrument 
               12  Instrument housing 
               14  Display 
               16  Tape cassette 
               18  Test element tape 
               20  Test element 
               22  Tape deflector 
               24  Lens element 
               26  Optical path 
               28  Optical measuring device 
               30  Outer wall 
               32  Light source 
               34  Converging lens 
               36  Front-facing pivot bearing 
               38  Side wall 
               40  Detector 
               42  Axis of rotation 
               44  Zenithal line 
               46  Front-facing conical bearing 
               48  Side surface 
               50  Cassette tip 
               52  Tape guide surface 
               54  Opening in the wall 
               56  Opening in the wall 
               58  LED 
               60  Instrument mainboard 
               62  Deflecting mirror 
               64  Convex lens surface 
               66  Double convex lens surface 
               68  Central diaphragm 
               70  Rear side 
               74  Centre line