Abstract:
A test device for testing of analyte concentration in a fluid to be applied thereto, the device comprising a plurality of test members arranged in at least one stack and electrodes for engaging with electrode tracks on a test member. A pusher pushes a single test member from the stack so that it can engage with the electrodes. An actuation member is connected to the pusher, and moves it when operated by a user. The at least one stack of test members is enclosed in a magazine which is initially sealed by a moisture impermeable seal. A cutter is provided for slitting the seal and permitting a test member to be pushed from the magazine by the pusher when the first test member from the magazine is to be used.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a test device for measuring the concentration of an analyte in a fluid sample, notably to a test device for analysing blood glucose or other analytes in bodily fluids. 
     2. Description of the Prior Art 
     Diabetics regularly need to test samples of their blood to determine the level of blood glucose. The results of such tests may be used to determine levels of medication needed to treat the diabetes at the time. In one known type of system, disposable sensors are used to test the blood. The sensors typically take the form of test strips which are provided with a reagent material that will react with blood glucose to produce an electrical signal. Conductive tracks on the test strip relay the electrical signal to a meter which displays the result. After a sample of blood has been applied to the test strip and the measurement has been taken, the test strip is disposed of. In order to couple the conductive tracks on a test strip with the meter, the test strip needs to be inserted into a sensor holder prior to the start of testing. The sensor holder has corresponding electrodes which are brought into electrical contact with the conductive tracks of the test strip. Test devices are known in which a plurality of test strip are provided on a cartridge disc. Each strip is housed in its own sensor slot, and means are provided to eject a test strip from its slot when required, and to automatically locate it in a sensor holder. Examples of test devices with test strip dispensers are described in U.S. Pat. No. 5,660,791, European Patent Application No. 0 732 590, and European Patent Application No. 0 738 666. 
     A problem with test strips is that they have only a limited shelf life, and exposure of test strips to the atmosphere reduces the shelf life further. Test strips open to the atmosphere will typically have a shelf life of about two to three months, whereas test strips which are sealed from the atmosphere will have a shelf life of about six to 12 months. 
     It has been proposed in WO 94/10558 to provide a stack of disposable test elements in a cylindrical housing, the stack being urged towards a test station to form a liquid-proof seal. In DE 196 39 226 A1 it is proposed to provide a test device with a cartridge that may have a plurality of chambers containing test strips, each of which chambers may be individually sealed to preserve the shelf life of the strips therein. A user removes the seal for each chamber when required, and a timing circuit may be activated either by the user or when the cartridge is pushed into the device. After a set time period has elapsed, an alarm or other indication reminds the user that the time period for using the strips has elapsed. 
     It is an object of the present invention to provide an improved test device. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a test device for testing of analyte concentration in a fluid to be applied thereto, the device comprising:
     a) a plurality of test members arranged in at least one stack, each of said test members carrying reagent means for producing an electrical signal in response to the concentration of analyte in an applied fluid, each of said test members having a plurality of electrode tracks for transmitting said electrical signal;   b) a housing having electrodes disposed therein for engaging with the electrode tracks on a test member at an engagement location;   c) a meter connected to the said electrodes and disposed at least partly in the housing, having electronics means for producing a signal output which is dependent on the electrical signal from a test member when the test member is engaged with the said electrodes;   d) a pusher which is adapted to push a single test member from the stack and into the engagement location where it can engage with the said electrodes and where the test member can be accessed to apply a fluid thereto;   e) an actuation member operably connected to the pusher, the said actuation member being operable by a user to move the pusher;   f) the or each stack of test members being enclosed in a magazine which is initially sealed by a moisture impermeable seal; and   g) wherein means are provided for breaking the said seal and permitting a test member to be pushed from the magazine by the pusher when the first test member from the said magazine is to be used.   

     The device may be disposable and may be pre-loaded with all the test members. At the point of final assembly, test member and meter calibration constants, expiry date information and units of measurement may be downloaded into the meter by suitable means, for example via a bi-directional RS232 bus. This has the advantage that each meter may be uniquely matched to the specific batch of test members used within the device. The meter and associated test members can be quality controlled as a single unit and by removing the need for a user to input calibration data, as in a conventional meter, user error of this function may be eliminated. 
     The software may also prevent the device from being used outside the overall product expiry date and may be programmed to prevent test members from an opened magazine from being used beyond its specific expiry period. 
     Because the seal on a magazine is automatically broken only when the first test member is to be used, the shelf life of each stack is maximised, and the user is not required to take any action other than to operate the device. 
     The test members will typically be elongate test strips, and the invention will be described herein with reference to such test strips. However it will be understood that the test members may be of any desired shape and profile. 
     In a preferred embodiment, a plurality of magazines are provided in a movable cartridge. Each magazine is sealed until a test strip therein is required for use, whereupon the cartridge moves to bring the magazine into a position for use, and the seal is broken. This process is preferably automated and requires no user input. Any number of magazines may be employed, each containing any desired number of test strips. For example, each magazine may have 20 test strips and there may be 5 magazines, so that the device is usable for 100 readings before being discarded. 
     The actuation member may be mechanically linked to the pusher, directly or indirectly, or it may be linked electronically, for example by actuating an electric motor which drives the pusher. In a preferred embodiment the actuation member comprises a plunger which the user presses. The plunger may act on the pusher via another member, notably a sliding member which has a cam surface. It will be appreciated that many other suitable arrangements may also be employed. 
     The seal may be broken on one side by a blade past which the magazine is moved, to permit a test strip to be pushed out. The seal may be broken at the other side and along the top by one or more cutting surfaces at the leading edge of the pusher, so that the pusher initially both cuts the seal and pushes the top test strip to the engagement location. However, it would also be possible for the pusher to cause the test strip to break through the seal without the need for a separate blade. To facilitate this, the region of the seal through which the test strip will pass may be provided with a frangible line of weakness. 
     In a preferred embodiment, each test strip comprises a base member having a working area to which the fluid is to be applied, containing the reagent means, and a non-working area adjacent to the working area, wherein the total thickness of the test member in at least a portion of the non-working area is at least as great as the total thickness of the test member in the working area. 
     By making the non-working area at least as thick as the working area, scuffing or abrasion of the working area in a stack can be reduced. Moreover, if a compressive load is applied to a stack of the test members, this may be spread out over a greater area, thereby reducing the possibility of compressive damage to the working area. 
     In a preferred embodiment, at least a part of the non-working area is of greater total thickness than the thickness of the working area. This further reduces the likelihood of damage to the working area by scuffing or abrasion when in a stack. The difference in thickness is preferably from 1 to 20 μm, notably from 5 to 10 μm. 
     To build up the working area, a plurality of layers are sequentially applied to the base layer, for example by screen printing, typically with curing or drying steps between the application steps. The layers which are printed typically comprise electrode patterns, a reagent layer, and a mesh layer (for spreading out an applied fluid). As a result of the application of these layers, the working area of a conventional electrochemical test strip is typically about 100 μm thicker than the non-working area, which contains the electrode tracks and, typically, a dielectric layer. A stack of 100 test strips will therefore be about 10 mm thicker in the working area than in the non-working area. In a test strip in accordance with the present invention, at least a part of the non-working area may be made thicker by any suitable means. Suitable means include, for example: a printed relief ink; an applied pad or tape; embossing of the base layer or an intermediate layer; or an extension of the mesh layer from the working area. 
     Further objects and advantages of the invention will be apparent as the description proceeds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be further described by way of example with reference to the following drawings, in which: 
         FIG. 1  illustrates user actions in operating a test device in accordance with the present invention; 
         FIG. 2  shows the assembly of a cartridge for use in the device of  FIG. 1 ; 
         FIG. 3  illustrates the action of the pusher in opening the seal on a magazine; 
         FIG. 4  illustrates the action of the pusher on a test strip; 
         FIG. 5  shows a mechanism for operating the pusher; 
         FIG. 6  is an exploded view of part of the device of  FIG. 1 ; 
         FIG. 7  is an exploded schematic view illustrating the cartridge advance mechanism; 
         FIG. 8  shows steps in the advance of a cartridge; 
         FIG. 9  shows sectional views through part of the cartridge advance mechanism at different stages; 
         FIG. 10  illustrates an alternative embodiment in which magazines are releasably connected together; and 
         FIG. 11  is a top plan view of a test strip in a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The test device shown in  FIG. 1  comprises a housing  2  which houses a meter with a visible display  4 , in this example, an LCD. A plunger  6  is released for use by the user pressing a release button which operates a catch.  FIG. 1   a  shows the device after a user has depressed the release button with his right index finger. To take a reading of blood glucose concentration, the user partially depresses the plunger  6  to an intermediate position, causing a test strip to be presented for receiving a sample of blood ( FIG. 1   b ). After the blood has been applied to the test strip, a reading is displayed on the display  4  ( FIG. 1   c ). The user then fully depresses the plunger  6  so that it is again engaged by the catch, causing the test strip to be ejected. The device is then ready for another reading to be taken.  FIG. 1   d  illustrates the device after the test strip has been ejected and after the user has again pressed the release button to free the plunger  6 . The various mechanisms involved in this process will be described below. 
     As shown in  FIG. 2 , a stack of test strips  8  is loaded in a magazine  10 , which is in turn located in cavity  74  in a cartridge  12 . In this example there are five cavities  74 , each of which houses spring means  14 , in this example a helical spring. Each cavity has an opening  18  through which a test strip  8  will be pushed by a pusher  16 . The spring urges the stack of test strips  8  upwards so that the top strip is engageable by the pusher  16 . A foil seal  20  seals the cavities  74  containing the magazines  10 . The slitting of the foil seal  20  will be described below, with reference to  FIG. 3 , which shows progressive movement of the pusher  16 . 
     Advancement of the cartridge  12  moves it past a blade  22  which is mounted in the housing  2  of the test device. The blade  22  makes a slit in the foil seal  20  at one end, through which a test strip  8  is to be pushed. The pusher  16  is moved from one end of the cavity  74  to the other, as illustrated by positions ( 1 ) through ( 5 ) of  FIG. 3 . As the pusher  16  moves, cutting surfaces  24  on its leading edge cut the foil seal  20  and push the uppermost test strip  8  out through the opening  18  to the testing position ( 4 ) (corresponding to that shown in  FIG. 1   b ), where a test reading can be taken. Fully depressing the plunger  6  moves the pusher  16  further towards the opening  18  and ejects the test strip  8 . In subsequent drawings, the seal  20  is omitted for clarity. 
     Referring now to  FIG. 4 , a mechanism is illustrated whereby movement of the pusher  16  from the position in  FIG. 4   a  initially pushes the test strip  8  out of the housing and then the head  28  of the pusher  16  bears down on the electrodes  26  of the meter so as to bring them into engagement with electrode tracks on the test strip  8  ( FIG. 4   b ). After a reading has been taken, further advance of the pusher  16  ( FIG. 4   c ) takes the head  28  beyond the electrodes  26 , which disengage from the test strip  8  and permit the pusher  16  to eject the test strip. 
     The mechanism for advancing the pusher  16  is illustrated in  FIG. 5 . The assembly shown in  FIG. 5  comprises a slider  32  which is operatively connected to the plunger  6 . The slider  32  is slidably mounted on a chassis top  36  which receives a groove plate  34 . The groove plate  34  has a groove therein which receives a sprung detent member  52  of the slider  32 , the function of which will be described later. Also provided on the slider  32  is a ratchet driver  44  which engages with a ratchet wheel  40 , the operation of which will be described later. A ratchet driver guide  38  is provided on the housing base  42 . The back housing member  46  (and front housing member  64 — FIG. 6 ) have cartridge tracks therein, along which the cartridge  12  can move. In the start position shown in  FIG. 5   a , the user presses the release button (not shown) where indicated by the arrow  30 . This releases a catch  58  ( FIG. 6 ) on the slider  32 . A spring  60  ( FIG. 6 ) pushes the plunger  6  and the slider  32  in the direction of the large arrow in  FIG. 5   b . The slider  32  has a hockey stick-shaped slot  31  in which is received the pusher  16 . As the slider  32  travels, it moves the pusher  16  in the direction of the small arrow  50  shown in  FIG. 5   b . At 6 mm before the end of travel, the pusher  16  is removed from the cartridge  12 . In the final 6 mm of travel the ratchet driver  44  indexes the ratchet wheel by one position, and advances the cartridge  12  so that the foil  20  on the first magazine  10  is slit at one end. The user then pushes the slider  32  to an intermediate position ( FIG. 5   c ) and in so doing, causes the pusher  16  to move back, with its cutting surfaces cutting the foil as previously described, and pushing the uppermost test strip out of the housing  2 . The slider  32  is held in the intermediate position by engagement of the sprung detent member  52  in the groove of the groove plate  34 . The detent member  52  and groove plate  34  operate in the manner of a ballpoint pen advancing and retracting mechanism, with the detent member  52  cycling around the groove in the course of one test cycle. After a reading has been taken, the plunger  6  is then fully pushed in by the user ( FIG. 5   d ), causing the slider to return to the position shown in  FIG. 5   a  and causing the pusher to eject the used test strip  8 . The slider  32  is now held in place until the next test reading is required.  FIG. 6  shows some of the components more clearly, including the chassis cartridge end  70  which has a cartridge drive spring  68 . A pusher “parking slot” plug  56  is mounted in the back housing member  46 , where the pusher  16  is kept away from the cartridge  12  to permit movement of the cartridge. An optional sensor exit slot plug  66  is provided in the front housing member  64 . A PCB  54  provides the meter electronics. When the test device is first used, and when a magazine is first opened up, a microprocessor on the PCB starts a timer counting down whereby the display  4  indicates when a particular magazine has exceeded its recommended life, or in the event that all magazines have exceeded their shelf life. 
       FIG. 7  shows the cartridge advance mechanism as an exploded schematic, with the cartridge in half-section. The cartridge  12  is urged by the spring  68  in the direction of the arrow  72 . Underneath the cartridge  12  there is provided a plurality of cartridge location pegs  76 , which are spaced apart by the width of the magazines, ie the distance between the centre lines of the magazines  10 . There is a peg  76  for each cavity  74 , and an additional leading peg on a front lip of the cartridge  12 . The ratchet wheel  40  has a keyway  78  thereon for the cartridge location pegs  76  to pass through as the cartridge  12  advances. The ratchet wheel is driven by the ratchet driver  44  which, cooperating with a pawl  62 , drives the ratchet wheel  40  in a clockwise direction as viewed in  FIG. 7 . The ratchet driver  44  reciprocates in both directions ( 80 ), but is sprung only in the direction indicated by the arrow  82 . A cartridge final stop member  84  is provided at the proximal end of the housing base  42 . 
     After each advance of the cartridge  12 , it remains stationary until the test strips in a magazine have been used up. At this point the cartridge  12  advances by the width of a magazine. The mechanism for controlling advance of the cartridge  12  is described with reference to  FIGS. 8 and 9 . Starting from the position shown in  FIG. 8   a , the ratchet mechanism is in a rest position ready for use. The centre line  86  of the active magazine  12  is in the keyway of the ratchet wheel  40 . The user presses the release button and the ratchet driver  44  travels in the sprung direction (arrowed— FIG. 8   b ). The ratchet driver  44  engages the ratchet wheel ( FIG. 8   c ) and rotates or indexes the ratchet wheel by one place (arrowed— FIG. 8   d ).  FIGS. 8   d  through  8   h  shows the cartridge advancement sequence. As the ratchet wheel  40  advances from the position shown in  FIG. 8   e  to that of  FIG. 8   f , the two foremost location pegs  76  of cartridge  12  are freed to advance through the keyway  78 . The location peg  76  furthest to the left in  FIG. 8   f  acts against the inclined surface of the keyway  78  while exiting the keyway. This forces the ratchet wheel  40  to rotate one place ( FIG. 8   g ) while the second location peg  76  is moved to the centre of the ratchet wheel. The rotation of the ratchet wheel  40  presents a solid stop wall at the point  88  to the oncoming location peg. At the position shown in  FIG. 8   h,  the cartridge has advanced by one magazine width, and the location peg  76  of the magazine behind the new active magazine comes to rest against the ratchet wheel stop wall, aligning the next magazine ready for use. 
     When the cartridge  12  is loaded in the housing during manufacture, the front location peg  76  is located in the keyway  78  and the ratchet wheel  40  is located so that the first time the ratchet wheel is indexed, the foremost magazine  10  is advanced as describe above, and the seal is cut by the blade  22 . 
     Because there are 20 test strips per magazine, and 20teeth on the ratchet wheel, the ratchet wheel is constructed to permit cartridge advance only once during a complete (360°) rotation.  FIGS. 8   i  and  9   a  show how, with the ratchet wheel at position  10  (180° rotation), the cartridge  12  is prevented from premature advancement. The cartridge location peg  76  is prevented from entering the ratchet wheel keyway  78  through incorrect orientation and misalignment. The cartridge base  90  and location peg  76  are shown separated from the ratchet wheel in  FIGS. 9   a  and  9   b  for clarity. With the ratchet wheel at position  11  ( FIGS. 8   j  and  9   b ) the location peg  76  is also misaligned with the ratchet keyway  78  and the cartridge does not advance. 
     An alternative embodiment is illustrated with respect to  FIG. 10 . Here, the magazines are releasably connected together, in this example by a dovetail joint (FIG. 10 b ). Used magazines  10  project through an opening in the housing and can be removed by the user.  FIG. 10   a  shows plan views before (top) and after (bottom) a used magazine has been slid off from its neighbour. In this embodiment the housing can be made smaller because it need not accommodate used magazines. 
     The test strip  8  shown in  FIG. 11  comprises a planar base member  92 , in this example of poly(butylene terephthalate) (PBT) (Valox® FR-1 from GE Plastics). The strip is 30 mm×5.5 mm, and 0.5 mm thick. A working area  94  is of conventional construction, comprising a plurality of electrodes, a reagent layer in intimate contact with the electrodes, and a mesh layer for spreading out a drop of fluid to be received on the working area. Electrode tracks  102 , for example of carbon, in the non-working area  98  of the test strip are connected to the electrodes in the working area  94  in known manner. Also in known manner, a dielectric layer  96  is printed around the working area  94  so as to overlie a portion of the electrode tracks  102 , leaving just the ends of the tracks exposed for connection to corresponding  26  electrodes on the meter. The layers are applied to the base member as inks, by screen printing. Each ink layer is about 10 to 20 μm thick, and the mesh is about 59 to 67 μm thick. The working area  94  has a total thickness which is about 100 μm thicker than the non-working area  98  up to the dielectric layer  96 . 
     To increase the thickness of parts of the non-working area, a high relief ink  100  has been printed in four strips. The high relief ink has a dried thickness such that the total thickness of the non-working area to which the high relief ink  100  has been applied is slightly greater than the total thickness of the test strip in the working area  94 . Thus, when a stack of such test strips  8  is formed, and a compressive load is applied to the stack by the spring  14 , the working area  94  will not bear all the compressive load. Scuffing of the test area will be reduced compared to a conventional test strip in which the working area stands proud of the non-working area. 
     Although this embodiment has been illustrated with reference to the use of a high relief ink printed in strips, it will be understood that it is not limited to this embodiment. The ink could be printed as a continuous block, and it could entirely surround the working area if desired. Instead of, or in addition to, the high relief ink, other means could also be provided to increase the thickness of the non-working area, for example: an applied pad or tape; embossing of the base layer or an intermediate layer; or an extension of the mesh layer from the working area into the non-working area. 
     Although the invention has been described with reference to a test device for measuring blood glucose concentration, it is to be understood that the invention is not limited to this application. The invention may be used in the determination of any analyte in a fluid by the use of suitable reagents in the test strip. Such reagents are well known to those skilled in the art.