TEST STRIPS WITH A SAMPLE ABSORPTION CAPACITY WHICH CAN BE SPECIFIED

Abstract: The invention relates to a test strip with a sample absorption capacity which can be specified and a process for its production. In this test strip, the reagent strip is fixed in a depression on the carrier. The size of this depression determines the volume of sample which can be absorbed. The excess of sample liquid is taken up by an absorbent material on the edge of the depression.

Description: The invention relates to a test strip with a sample absorption capacity which can be specified and a process for its production. In this test strip, the re­ agent strip (3) is fixed in a depression on the carrier (1). The size of this depression determines the volume of sample which can be absorbed. The excess of sample liquid is taken up by an absorbent material (6) on the edge of the depression. The importance of test strips as analytical agents, especially in the field of clinical chemistry, has increased more and more in the last few years. One field of use is, for example, monitoring of the blood sugar level by diabetics themselves. A similarly impor­ tant field of application is the use of such test strips by primary care physicians as a rapid diagnostic aid. Metering of the sample is a great problem. If the test strips are used for qualitative investigations, the volume of sample is of no significance. However, if the test strips are used for quantitative analyses, exact metering of the sample is necessary. By their nature, however, reagent strips themselves are not suitable for absorbing an exact and reproducible amount of sample liquid. The sample is therefore usually metered with the aid of pipettes. This can be carried out reproducibly and with the required accuracy only by specialized per­ sonnel in laboratories, but not in applications in, for example, self-diagnosis. It is also frequently necessary to wipe the re­ agent strips in order to remove constituents in the sample liquid which interfere with the measurement, such as, for example, red blood corpuscles in the analysis of whole blood. As a result of this wiping process, there is the possibility that sample liquid will be pressed or sucked out of the reagent strip. The present invention was based on the object of providing a test strip which has a sample absorption capacity which can be specified, that is to say a test strip in which a precisely predetermined amount of sample liquid gets into the reagent strip. An excess of sample is automatically removed. The invention relates to a test strip with a sample absorption capacity which can be specified, in which the reagent strip (3) is fixed in a depression on the carrier (1), the size of the depression determining the volume of sample which can be absorbed and the depres­ sion having on its edge an absorbent material (6), which serves to take up excess sample liquid. In this arrange­ ment the carrier (1) has the shape of a profile with one or more depressions for accommodating the reagent strips (3). Suitable carriers are all the materials known for this purpose, such as, for example, hard papers or plas­ tics. Particularly suitable materials are thermoplastics, such as, for example, poylethylene, polypropylene, poly­ amides or polyesters, which extruders can be employed with such plastics to produce the carrier profiles. The carrier profiles can, however, also be produced by com­ bining several components, which are then bonded to one another, for example, by glueing. The reagent strips (3) can consist of the mater­ ial customary and known for each particular purpose, such as, for example, paper, gelatine, cellulose or plastic. Reagent strip (3) is understood here as a carrier matrix which contains the particular reaction substances necessary for the analysis, such as, for example, enzymes, substrates, coenzymes and indicators. The reagent strip can consist of one (single layer) or several (muLtilayer) layers. The absorbent material (6) on the edge of the depression which serves to take up the excess sample can be, for example, paper or fabric. However, plastics which are capable of absorbing liquids, in particular water, are also suitable. The ability to absorb liquid can be con­ siderably influenced by pretreating the absorbent mat­ erial, for example by wetting agents or introduction of functional groups. Test strips can furthermore be provided with a cover (2) in which there is an opening for application oi the sample. Between this application point for the sample (5) and the reagent strip is preferably an inter­ mediate layer which serves to remove undesired constitu­ ents from the sample (5). This intermediate layer can have, for example, filtration properties for removing blood cells. The undesired constituents of the sample can, however, also be bonded to this intermediate layer by ad- or absorption. This can be effected, for ex­ ample, by functional groups (ion exchangers) or also antibodies. Undesired constituents of the samples are to be understood as substances which are capable of influencing the desired detection reaction or the measurement of this reaction. The intermediate layer (4) can also improve the distribution of the sample on the reagent strip (spreading layer). An essential feature in the production of the test strip according to the invention is the carrier (1), which must have the shape of a profile with one or more depressions. Such a profile can be produced, for example, with the aid of extruders or by combining and subsequently bonding several components. The reagent strip (3) is laid and fixed in this depression. The absorbent mater­ ial (6) is applied and likewise fixed on the edge of the depression. Fixing can be effected either with the aid of adhesives or adhesives by shaping the carrier. Shaping is effected by heat and/or pressure. By shaping the carrier, a type of "press fit" is produced, which holds the reagent strip (3) and/or the absorbent material (6) firmly on the carrier (1). Introduction of the reagent strip by pouring is also suitable. If the carrier matrix for the reagent strip consists, for example, of plastic, this can be introduced into the depression in the form of a solution, in the molten state or as mono­ mers. Hardening is then effected by drying, cooling or polymerization. In the use of, for example, gelatine as the carrier matrix, it is thus to be regarded as advan­ tageous to introduce this into the depression in the molten state. The reagents necessary for the analysis can be added to the carrier matrix before pouring into the depressions, or can be introduced by an impregnation operation after hardening of the carrier matrix. A test strip according to the invention is shown and a process for its production is described below by way of example in Figures 1 to 5. Figure 1 shows a longitudinal section of a test strip. A reagent strip (3) is laid and fixed in the carrier profile (1). Above the reagent strip is an intermediate layer (4), which can be used for holding back undesired constituents of the sample. It also ensures uniform distribution of the sample (5). In this example, this intermediate layer (4) is bonded firmly to the cover (2) via the connecting point (8), as shown in Figure 2. After the sample has been applied to the test strip and has become distributed, the cover with the attached intermediate layer can be removed, together with the undesired constituents of the sample. The test strip can then be subjected to measurement. Figure 2 shows a cross-section of the test strip. Figure 3 Shows a plan view of the test strip with the cover (2) in which there is the opening for application of the sample. The depres­ sion (9) around the opening facilitates the guiding of the sample towards this opening. Figure 4 shows a section from Figure 1 in which the arrangement of reagent strip (3), intermediate layer (4) and absorbent material (6) in relation to one another is shown again. Figure 5 shows a greatly enlarged view, by way of example, of the fixing of the pressed-in reagent strip, which is effected by means of heated pressure rolls by plastic shaping (left) or, preferably, by ultrasonic shaping (right), the ultrasonic booster effecting shaping of the carrier (1) in the region of the web (7) without contact, and thus producing a firm connection. In this figure (as also in Figure 1, Figure 2 and Figure 4), the carrier has an opening below the reagent strip. Measurement can be effected through this opening (for example reflection, emission of light or fluores­ cence). If transparent reagent strips are used, measure­ ment can also be effected with an absorption photometer. Such an opening can be dispensed with, however, with transparent carriers. As already mentioned above, the test strip can, however, be introduced into the depres­ sion by pouring, which makes separate fixing of the reagent strip to the carrier unnecessary.

Claims: 1. Test strip with a sample absorption capacity which can be specified, characterized in that the reagent strip (3) is fixed in a depression on the carrier (1), the size of the depression determining the volume of sample which can be absorbed and the depression having on its edge an absorbent material (6), which serves to take up excess sample liquid. 2. Test strip according to Claim 1, which is addi­ tionally provided with a cover (2) in which there is an opening for application of the sample. 3. Test strip according to Claims 1 and 2, charac­ terized in that between the reagent strips and the appli­ cation point for the sample is an intermediate layer (4), which is permeable to the sample, for removing undesired constituents of the sample. 4. Test strip according to Claim 3, characterized in that the intermediate layer (4) has filtration proper­ ties for removing blood cells. 5. Test strip according to Claims 3 and 4, charac­ terized in that the intermediate layer (4) consists of a material which bonds the undesired constituents of the sample by ad- or absorption. 6. Test strip according to Claims 2 to 5, charac­ terized in that the intermediate layer (4) and the cover (2) are firmly bonded to one another and can be removed together from the test strip. 7. Test strip according to Claims 1 to 6, charac­ terized in that the absorbent material (6) used to absorb the excess sample can be paper, fabric or a plastic which absorbs liquid. 8. Process for the production of test strips with a sample absorption capacity which can be specified, characterized in that a) a carrier (1) is produced in the shape of a profile with one or more depressions for accommodating one or more reagent strips (3), the size of the depressions determin­ ing the volume of sample which can be absorbed, b) the reagent strips (3) are introduced into the depressions by pouring or laying in and, if necessary, are fixed by glueing or shaping the carrier and c) an absorbent material (6) is applied to the edge of the depression(s) for taking up excess sample liquid. 9. Use of test strips according to Claims 1 to 7 for the detection of one or more analytical substances in a liquid.

Inventors: ENGELMANN, HELMUT, DIPL.-ING.
Applicants: MILES INC.
Application year: 1986
Main classification: G01N33
IPC codes: G01N33, G01N31