Abstract:
The present invention provides a test tape unit suitable for testing blood sugar. The test tape unit comprises an analytical test tape, a feed spool for unwinding unused test tape, a take-up spool for winding used test tape, and a tape guide to expose a section of test tape at a measuring site for receiving an application of body fluid. The tape guide has a flat support frame which stretches the test tape at the measuring site and forms the border of a measuring opening which is kept free from optical elements for producing an optical measurement.

Description:
RELATED APPLICATIONS 
     This application claims priority to EP 06 014 316.1, filed Jul. 11, 2006, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     In the past, diabetics have used individual test strips for self-diagnosis in which the strips were analyzed photometrically after applying a small amount of blood to the strip to determine the glucose content of the fluid sample as accurately and reliably as possible. In order to improve the user-friendliness of this test system, it has been proposed that such testing be performed on a test tape in the form of a tape cassette. It is possible to insert tape cassettes as a disposable component into compact hand-held devices to automatically and rapidly carry out all required analytical steps. In these tape cassette testing systems, the disposable components are mass produced and high demand occurs due to the reliability. 
     Accordingly, document WO 2005/006985 discloses a test tape guide curved in an arch that exposes a section of test tape to receive an application of liquid on the front side and to perform an optical measurement on the rear side by means of a reflection-photometric measuring unit focusing on this area. However, with this arrangement having parallel arched rails, there is a risk that in the case of a thin flexible test tape the central tape area will arch inwards under tension in the free space between the rails and thereby making an accurate optical focus more difficult. Such tape deformation has already proven to be problematic in the case of small radii of curvature, especially with regard to measuring optics having a short focal distance. 
     In order to overcome this problem, it has been proposed that optical elements in the form of cylinder lens be used as an application tip, wherein the lens bundles the measuring light in the optical path of the photometer. However, just as in the case of simple optical windows, care must be taken that high quality requirements are achieved for the required measuring accuracy especially with regard to transmission, scratch resistance, temperature resistance, coefficient of expansion, optical quality, and other material parameters or faults such as those listed in International Standard ISO 10110. 
     SUMMARY OF INVENTION 
     Embodiments incorporating the present invention address the described disadvantages of the prior art and further improve test tape systems while being simple to manufacture, provide special application advantages and high measurement accuracy with a low strain on the test tape. In particular, these embodiments are arranged without an optical component or material window in the area of the tape guide and thus optical elements which interact or interfere with the passage of light are avoided. 
     One embodiment of the tape guide has a planar support frame which holds the test tape section flat at the measuring site, wherein the frame has legs that circumscribe or border a clear measuring opening which is kept free from optical elements for an optical measurement to be taken on the rear side of the tape. This provides good targeting accuracy and adequate support for the application of liquid on the front side of the tape, while the test tape is held in a narrowly defined measuring plane without significant or noticeable bending. The “clear” measuring opening is provided as a simple optical entrance that allows light to be emitted into the opening and permits the passage of reflected radiation under constant conditions. According to this embodiment, it is unnecessary to manufacture special optical components such as lens, filters, or material windows. Also, by avoiding tape constriction, this embodiment provides an energy efficient and gentle tape transport. 
     In a similar embodiment, the frame legs of the support frame advantageously border the measuring opening in a rectangular shape and also provide sufficient space for several light beams oriented towards the test tape. 
     In another exemplary embodiment, the support frame has two parallel frame legs extending in the longitudinal direction of the test tape and the distance between the outer edges of these two legs is less than the width of the test tape. The portion of the test tape border that extends past the frame legs can thus provide a screen against contamination of the device by a sample of body fluid. 
     In another embodiment, the support frame has two parallel frame legs at right angles, or transverse, to the direction the test tape is transported, the length of which corresponds to at least the width of the test tape. This avoids tape constriction in the deflection area and supports planar frame stretching. These frame legs are referred to as “the transverse frame legs.” 
     In order to further improve the tape guide, it is advantageous when the frame legs of the support frame, which support the test tape in its longitudinal direction, are flattened into a strip shape. It is also advantageous when the transverse frame legs are rounded at a deflecting edge for the test tape. 
     In another advantageous embodiment, the support frame is formed by a flat top surface of a truncated, pyramid-shaped projection of the tape guide. This projection is also referred to as being tapered at its top surface. This tapered projection improves handling and hygiene when applying liquid to the test tape. 
     For the application of body fluid to the test tape, it is advantageous when the tape guide has deflecting bevels adjoining the support frame in the longitudinal direction of the tape, wherein the deflecting bevels are positioned at an acute angle with the plane defined by the support frame. 
     In order to secure the test tape against lateral deflection, the tape guide can advantageously have side boundaries or walls which are arranged adjacently outside of the support frame so that the test tape can be precisely centered on the support frame. 
     In addition, it is advantageous when the test tape is unwound from the feed spool by driving the take-up spool. Also, to keep the test tape flat at the measuring site, the test tape should be held in tension by return forces of more than 1 N. 
     It is advantageous for mass production to occur when the support frame is molded as one piece onto a molded part. The molded part can be an injection-molded part consisting of polypropylene, whereby the optical area is screened against the entry of scattered external light by a black coloring. 
     If the body fluid sample application and measurement take place at the same site, transporting the test tape section to a distant measuring site is not necessary. In an exemplary embodiment, it is advantageous when the body fluid is applied to the front side of the test tape section, which is supported by the support frame, and a reflectometric measurement is taken from the rear side of the tape, which rests on the support frame, with free radiation through the measurement opening. 
     In order to simplify the use of the device, it is advantageous when a measuring chamber delimited by the tape guide is used with a measuring unit, wherein a light source and a light receiver of the measuring unit are focused above the measuring opening onto the test tape section that is located above it. 
     The tape guide is advantageously covered from the outside by a cover part or housing, wherein the support frame protrudes from an opening in the cover part or housing. A test tape unit is designed as a tape cassette for being inserted into a test device. 
     Embodiments incorporating the present invention also provide a test system comprising a reflectometric measuring unit, a tape drive, and a test tape unit which are inserted into a hand-held device. 
    
    
     
       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 tape cassette for blood testing in which an outer cover or housing is removed to illustrate the interior components of the cassette; 
         FIG. 2  is an enlarged perspective view of a head portion of the tape cassette of  FIG. 1 ; 
         FIG. 3  is a top view of the head portion of  FIG. 2 ; and 
         FIG. 4  is a partial schematic view of a test system with a tape cassette inserted therein. 
     
    
    
     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. 
     The tape cassette  10  shown in  FIG. 1  enables large quantities of glucose analyses to be carried out on blood samples taken by a patient. In this exemplary embodiment, the tape cassette  10  comprises an analytical test tape  12  which is pulled from a feed spool  14  and wound over a tape guide  16  onto a take-up spool  18 . A section of test tape  20  is stretched flat over a planar support frame  24  at a measuring site  22  in order to apply body fluid to the front side of the test tape  20  and take a precise reflectometric measurement on the rear side. 
     The test tape  12  consists of a light-permeable carrier tape  26  on the front side in which test fields or elements  28  are applied in sections as labels. These test fields or elements contain dry chemicals which respond to the analyte, such as glucose, in the body fluid and lead to a measurable change in the light that is reflected back when the rear side is illuminated. The carrier tape  26 , for example, consists of a 5 mm wide and approximately 10 μm thick foil on the front side of which a detection film of 50 μm in thickness is applied in sections. 
     As the measurement is being taken, the measuring light is irradiated and reflected back through a measuring opening  32  bordered by the support frame  24  without optical elements such as lens, filters, or windows filled with material being present within the area of the opening, although the measuring opening can, optionally, be bordered by a diaphragm. This provides a defined rear-side focusing or alignment of the optical measuring unit on the test tape section  20  which is exposed flat over the measuring opening  32 . 
     In order to transport the test fields or elements  28  successively to the measuring site  22 , a tape drive engaging in the hub  34  of the take-up spool  18  enables the test tape  12  to be wound forward. In this embodiment, return forces of about 2 N are generated by friction on the feed spool  14  and in the area of the tape guide  16  (and especially at a passage seal  36 ) such that the test tape  12  is adequately placed under tension to ensure it lies flat on the support frame  24 . 
     The tape guide  16  is formed by an injection molded part made of polypropylene and provides support for the spools  14 ,  18 . A cover part or housing  38  is provided to cover the tape guide  16  from the outside and has an opening in a tapered narrow side wall for an easily accessible exposure of the support frame  24 . 
     According to the embodiment shown in  FIG. 2 , the support frame  24  is formed on a head portion  40  of the tape guide  16 . In this embodiment, the support frame  24  is formed at the flat top surface of a tapered projection  42  which has a truncated, pyramid-shape to facilitate a hygienic application of body fluid samples. Thus, in the longitudinal direction of the tape, deflecting bevels  44 ,  46  adjoin the support frame  24  to guide the test tape  12  along the opposing longitudinal sidewalls of the cassette  10 . Side boundaries or walls  48 ,  50  are provided in this area which secure the test tape  12  from lateral deflection and prevent the test tape  12  from slipping sideways and off the support frame  24 . 
     According to the exemplary embodiment shown in  FIG. 3 , the support frame  24  has two frame legs  52 ,  54  extending longitudinally in the same direction as the test tape moves (left-to-right in  FIG. 3 ) and two frame legs  56 ,  58  which are at right angles or transverse to frame legs  52 ,  54 . The longitudinal frame legs  52 ,  54  lay flat and the distance between the outer edges of the legs  52 ,  54  is less than the width of the test tape  12 . In this embodiment, the width of the test tape  12  extends past the sides of the legs  52 ,  54  and body fluid is prevented from reaching the projection  42  during application. The transverse frame legs  56 ,  58  are rounded off with a radius of approximately 0.3 mm at the deflecting edges  43  and their length is such that the entire width of the test tape  12  is supported thereon. With the test tape having a width of approximately 5 mm, the frame legs  56 ,  58  also have a length of 5 mm whereas the measuring opening  32  has a shorter length of 3 mm and width of 2 mm. This design of the support frame  24 , in addition to allowing hygienic handling, also prevents the stretched portion of test tape  20  at the measuring site from arching or bending. 
     In order to simplify handling the cassette  10 , the cassette  10  is inserted into a hand-held device  60  as illustrated in  FIG. 4 . The device  60  has a control and evaluation unit  62 , a tape drive  64  acting on the hub  34  of the take-up spool  18 , and an optical measuring head  66  positioned in the measuring chamber  30  on the cassette side. 
     The measuring head  66  and the head portion  40  of the cassette  10  are shown in  FIG. 4  in the transverse direction (i.e. to the right) from the test tape. The measuring head  66  comprises a light source  68  and a light receiver  70  on a printed circuit board  72 . A pair of lens  74 ,  76  in the measuring head  66  focus the light source  68  and the light receiver  70  through the transparent carrier tape  26  onto the test field or element  28 . In this embodiment, light beams  78 ,  80  on the transmission and receiving side pass through the measuring chamber  30  and, in particular, through the measuring opening  32  without any interaction or interference from optical components. This provides reflection-photometric detection in a defined measuring plane where the optical path is not adversely affected by components of the cassette  10 . 
     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.