System and method for analyzing a sample liquid

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.

Claims

1. A method of using a test system of the type having a tape cassette including a test tape carrying a plurality of test elements for analyzing body fluids, the method comprising: applying sample fluid to a test element of the test tape that is positioned at a sample application site, thereby creating a wetted area on the test element; irradiating the test tape with a light source while advancing the test element from the sample application site toward a sample measuring site; detecting light that is reflected from the wetted area of the test element; and using the detected light from the wetted area of the test element to determine when the wetted area on the test element is positioned at the measuring site.

2. The method of claim 1, further comprising interrupting the advancing of the test tape when the wetted area is determined to be positioned at the measuring site.

3. The method of claim 1, wherein the detecting step further comprises detecting a drop in reflectance followed by a rise in reflectance.

4. The method of claim 3, further comprising interrupting the advancing of the test tape upon detecting the rise in reflectance.

5. The method of claim 4, further comprising irradiating the wetted area with a second light source, detecting light from the second light source that is reflected from the wetted area, and correlating the detected light reflected from the wetted area to presence or concentration of an analyte in the sample fluid.

6. The method of claim 1, further comprising irradiating the wetted area with a second light source, detecting light from the second light source that is reflected from the wetted area, and correlating the detected light reflected from the wetted area to presence or concentration of an analyte in the sample fluid.

7. The method of claim 6, further comprising using a first detector for the step of detecting light from the light source that is reflected from the test tape and using a second detector to detect light from the second light source that is reflected from the wetted area.

8. The method of claim 7, further comprising interrupting the advancing of the test tape when the wetted area is determined to be positioned at the measuring site.

9. A method of using a test system of the type having a tape cassette including a test tape carrying a plurality of test elements for analyzing body fluids, the method comprising: applying sample fluid to a test element of the test tape that is positioned at a sample application site, thereby creating a wetted area on the test element; irradiating the test tape with a light source while advancing the test element with the wetted area from the sample application site toward a sample measuring site; detecting light from the light source that is reflected from the test tape as the test element with the wetted area is advanced; and using the light detection from the wetted area of the test element to position the test element.

10. The method of claim 9, wherein the step of using the wetted area of the test element to position the test element comprises measuring a change in reflectance of the detected light and associating the change in reflectance with the wetted area of the test element entering the measuring site.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 is a schematic plan view illustrating a test tape system for blood glucose determination;

(3) FIG. 2 is a diagrammatic view in partial perspective illustrating a positioning device for positioning the test tape at the site of measurement;

(4) FIG. 3 is a top view illustrating a section of test tape provided with test element;

(5) FIGS. 4a and 4b illustrate two diagrammatic side views of the positioning device aligned with the test tape;

(6) FIGS. 5a thru 5e illustrate different wettings of a test field with the corresponding reflectance signals; and

(7) FIGS. 6a thru 6e illustrate another embodiment of a positioning device illustrating a section of test tape in various positions in its advancement.

(8) Corresponding reference characters indicate corresponding parts throughout the several Figures.

DETAILED DESCRIPTION

(9) 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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 bather 44.

(14) 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. 4a 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. 4b 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.

(15) 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. 5a). In the case of the central wetting of the area 38 shown in FIG. 5b a lower reflectance value B is measured there corresponding to a color change in the reaction layer. FIGS. 5c and 5d 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. 5e.

(16) 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.

(17) 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. 4a) 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. 4a) 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.

(18) 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. 6a) and subsequently applied to the test field 14 after appropriate tape advancement (FIG. 6b). In the course of further tape advancement, the start of the wetted area 42 is detected by a first light barrier 62 (FIG. 6c). 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. 6d. 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. 6e.

(19) In addition to blood, it is also possible to analyze other sample or body fluids, in particular, interstitial fluid, in the manner described above.

(20) 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.