Test carrier for the determination of an analyte from whole blood and a process for the production thereof

~ 132~7~2 --1- The present invention is concerned with a test carrier for the determination oE an analyte Erom whole blood with the help of reagents contained in the test carrier, said test carrier having a blood application side, to which blood is applied, an evaluation side, on which, as a result oE the reaction of the reagents with the analyte, an optically detectable change takes place, and an erythrocyte separation means between the blood application side and the evaluation side. The present invention is also concerned with a process for the production of such a test carrler.

For the qualitative or quantitative analytical determination of components of blood, in recent times so-called carrier-bound tests have increasingly been lS used. In the case of these carrier-bound tests, reagents are embedded in appropriate layers of a solid test carrier which is brought into contact with the sample. The reaction oE sample and reagents leads to an optically detectable change, especially to a colour change, which can be evaluated visually or with the help of a de~ice, usually reflection-photometrically. Instead of a colour change, the reaction can also give rise to ~he formation of or to the change of another optically detectable signal, for example a fluorescence or a luminescence.

Test carriers are frequently formed as test strips which consist essentially of a longitudinal support layer ~. , - , , , ~ ~ .

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~ ~32~2 --2-oE synthetic resin material with test fields applied thereto. ~lowever, test carriers are also known which are formed as quadratic or rectangular platelets.

Carrier bound tests are characterised especially by the simplicity of the handling. It is all the more regretable that, with most of the previously known carrier bound tests, the blood cannot be used directly as so-called whole blood. On the contrary, it is necessary to separate oEf the red blood corpuscles (erythrocytes) in order to obtain colourless plasma or serum. This usually takes place by centrifuging, i.e.

an additional handling step ls necessary. Furthermore, a device for centrifuging is not available everywhere since carrier bound tests are, to an increasing extent~ also made available to lay persons. Centrifuging requires a relatively large amount of sample, whereas, on the other hand 9 the endeavour in clinical diagnosis is to suffice with a small blood droplet such as can be obtained by a prick in the finger.

Therefore, attempts have not been lacking to make available test carriers which make possible analytical determinations directly from blood.

Thus, from DE-B 1 5g8 153 and corresponding to US-patent 3 630 957 a test carrier is known with a film layer produced from an aqueous dispersion of natural or synthetic polymers in which are present the reagents necessary for the detection.

With this test carrier, certain analytical determinations, especially _3_ 1 3 2 ~ 7 ~ 2 the determination of glucose, can be carried out directly from the blood. However, in the case oE other analytical determinations, good results are no~ obtained with such test carriers 9 which may be due to the Eact that the component materials of the sample cannot penetrate into the film in sufficient amount.

From EP-A-16 387 and corresponding us-patent 4 312 834 is known a test carrier layer also based upon the use of a dispersion film former which avoids this probler,l in that it con-tains relatively large amounts oE (es pecially inorganic) small par-ticles.

With this there is obtained a universally usuable-test layer which, however, does not penmit a determination from whole blood because no-t only comparatively large sample colnponents to be analysed but lS also erythrocytes can penetrate into this layer unhindered.

From EP-A-45 476 and corresponding US-patent 4 477 575 it is known to use glass Eibres for obtaining serum or plasma on a test carrier.

This solution of the problem is universally us~ble but it is necessary to apply -the glass fibre layers to the test carxier in an appropriate way.

A comparatively complicated tes-t carrier construction thereby results and the production process is expensive.

Also, insofar as hitherto test carriers of the initially described type have been suggested, in which, on one side, blood can be applied without previous erythrocyte separation and the evaluation takes place : . . . . .

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, ,. - ~ ~ 132~7~2 --4-on the other side, an erythrocyte separation means thereby being present between the blood application side and the evaluation side, these attempts have not proved to be satis~actory.

In US-A-36 63 374 and in US-A-42 56 693~ a membrane Eilter is used in order to prevent the passage of the erythrocytes from the blood application side to the evaluation side.

In principle, mernbrane filters are admittedly suitable for filtering off erythrocytes.

However, the use thereo~ in test carriers has not been successful. The same applies ~o the combination of the membrane filter with a pre-positioned glass fibre layer, also mentioned in these US Patents, which is to prevent the blockage of the membrane filter with coarser particles. The production of such test carriers would be very expensive without a satisfactory function being achieved.

In US-A-4 ~69 817 and several other US Patents of the same Applicant, there is also discussed the possibility of providing in a test carrier an intermediate layer for preventing the passage of erythrocytes which, at the same time, contains light-blocking components in order to ensure that the light beams of the evaluation device cannot penetrate into the erythrocytecontaining layer. However, this Patent Speci~icationdoes not describe how the filtering of the ery~hrocytes could be achieved.

~ 132~7~2 -5 Therefore, the present invention seeks to provide a test carrier with which the carrying out of medicaldiagnostic determinations is possible directly from whole blood, the test carrier thereby being easy to handle and simple and economic to produce.

Thus, according to the present invention, there is provided a test carrier for the determination of an analyte from whole blood with the help of reagents contained in the test carrier, said test carrier having a blood applica tion means, to which blood is applied, an evaluation means,in which, as a result of the reaction of the reagents with the analyte, an optically detectable change takes place, and an erythrocyte separation means in the fluid path between the blood application means and the evaluation means, wherein the erythrocyte separating means includes a laminated composite structure having a first zone, which contains a polymeric film former, kieselguhr and a pigment, and thereupon, with formation of a transition region, a second zone, containing a polymeric film former, formed by liquid coating the first zone. With respect to the fluid path of the sample in the test carrier the first zone is directed towards the blood application means and the second zone is directed towards the evaluation means and each of such zones is - at least in use of the test carrier - in fluid communication with the corresponding means.

By means of the present invention, a test carrier is provided for whole blood analysis, which comprises an erythrocyte retention means which is formed by a process which : .

~ ~325~2 is easy to carry out. The passage of -the plasma from the first zone into the evalua-tion zone takes place in a few seconds so that a rapid evaluation is possible. Handling is simple, especially since the applied blood does not have to be wiped off or washed off, as was frequentl~ necessary in the case of previously known test strips.

The process according to the present invention for producing such a test carrier requires two dif~erent coating masses which9 in separate coating steps 9 are each formed to give a thin layer. Besides a polymeric film former dispersed or dissolved in the carrier liquid, the first coating mass contains kieselguhr, a pigment and known adjuvan~ materials, for example buffers, wetting agents, thickening agents, defoamers and the like. l'he second coating liquid also contains a dispersed or dissolved polymeric film former.

For the production of a composite laminate consisting of a first zone and a second zone, the first coating mass is first formed on a substrate into a thin layer and dried. Thereafter, on this layer, the second coating mass is formed to give a thin layer and dried, components of the second coating liquid thereby penetrating into the first formed layer. Therefore, the first zone and the second zone are not separated from one another by a sharp boundary but rather ~here is formed a transition region in which they progressively pass over into one another.

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_7_ ~ 13~7~ Thus, broadly stated, in one aspect the present invention provides a test carrier for supporting test reagents for the determination of an analyte from whole blood, comprising a blood reception side for receiving whole blood, the analyte of which is to be determined, an evaluation side on which, as a result of a reaction of the reagents, supported by the carrier, with the analyte, an optically detectable change takes place, and an erythrocyte separation means between the blood reception side and the evaluation side, said erythrocyte separation means comprising a laminated composite having a first zone containing a polymeric film former, kieselguhr and a pigment in opposed relationship with a second zone containing a polymeric film former, and a transition region between said first and second zones, said first zone facing the blood reception side, and said second zone facing the evaluation side of the laminated composite.

It will be understood that the test carrier of the invention includes as a component tes-t reagents for the determination of an analyte from whole blood supported thereby.

~` ~L32~7~2 --8- In a particular embodiment the laminated composite may be mounted on part of a liquid transport layer supported on a base film such that the blood reception side is in liquid flow communication with the liquid transport layer. The liquid transport layer has an exposed blood application zone and the transport layer is adapted to permit or effect flow of whole blood applied to the blood application zone to the blood reception side of the composite.

The kieselguhr is believed to act in conjunction with the transition region to achieve efficient separation and holding of erythrocytes in the first zone.

The pigment may also contribute to this separation and holding of erythrocytes in the first zone.

The pigment functions to scatter light entering the first zone from the second zone during optical determination at the evaluation side, whereby interference by red blood coloured matter retained in the first zone is avoided.

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t ~32~7~ g Preferred polymeric film formers include organic synthetic resins, s~ch as polyvinyl esters, polyvinyl acetates, pol-yacrylic esters~ polymethacrylic acid, polyacrylamides, polyamides and polystyrene. Apart Erom homopolymers, there are e~specially also ~reEerred co-polyrners, for example of butadiene and styrene or of maleic acid esters and vinyl acetate, as well as terpolymers. ~lowever, further film-forming, natural or synthetic organic polymers, as well as mixtures thereof, can also be used. Gelatine is not suitable.

The film formers can be dissolved in appropriate organic solvents. It is oEten advantageous to use a dispersion of an appropriate film Eormer, in which case the preferred carrier liquid is water.

Dispersion film fo~mers contain submicroscopic polymer particles insoluble in the carrier liquid which are dispersed in ve~y fine distribution in the carrier liquid. If, during ~ilm Eormation, the liquid is removed by evaporation or volatilisation, then the particles approach one another and finally touch. Due to the thereby occurring large forces and an increase of surface energy involved with the film formation, the particles grow together to give a ~ubstantially unbroken film layer. Further details in this regard are to be found, for example, in the article "Latex Film Formation", by J.W.

Vanderhoff in Polymer News, 1977, pages 194 - 203.

... . . .. . . i. . .. .

~ 132~7~2 -10 Kieselguhr is also called diatomaceous earth.

This is a deposit, resulting from the silicic acid structures of types of diatoms, which is mined in various places. The kieselgu~lr preEerably used has an average particle diameter of 5 - 15 ~m., these values being determined with a laser granulometer Type 715 which is marketed by the firm Pabisch, ~unchen, FP~G.

The pigment pre~erably consists of particles with an average diameter of from about 0.2 -to 0.7 ym.

Titanium dioxide is, for example, especially preferred.

~owever, other pigments can also be used, the particle sizes oE which usually lie substantially in the given range, which correspond approximately to the wavelength spectrum of visible light. A maximum light scattering and thus a highly covering pigment is thereby achieved.

The reaction time in the laminated composite is shortened when this preferably has a maximum thickness oE 0.6 mm. and especially preferably a maximum thickness of 0.2 mm.

As substrate for the forming of the first coating mass, there can be used, for example, a plate of glass or of another material from which the film layer can easily be removed.

It is thereby possible to remove the finished laminated composite and, for example, to mount it on a transparent support film, the evaluation side thereby facing the support film so that the blood application side of the larninated composite is freely accessible.

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32~7~2 Substantially simpler in the production and, therefore, preferred is the fixing of the laminated composite on to a porous support layer, ~he blood application side thereby facing the support layer.

This is preEerably achieved by the direct use of the porous support layer as substrate for the forming of the Eirst coating mass. In ~he case of such a larninated composite~ a free entry of air to the detection zone is possible, the reaction time in this zone thereby being considerably shortened in many cases. End point determinations are thereby possible.

As porous support layer, there can, in principle, be used any open, planar composite structure, i.e. any structure which extends flatly and is sufficiently open to enable blood to penetrate sufficiently quickly. A sieve-like structure of a synthetic resin material with very many holes arranged close to one another could, Eor exarnple, be used. Preferably, howeverl the porous support consists of a textile material and especially of a woven or knitted f~bric, which can be produced, for example, frorn polyamide, polyester or silk. A fleece or paper can possibly also be used. Appropriate materials are described in EP-A-113 896.

The present invention will now be described ln more detail in the following on the basis of embodimental examples illustrated schematically in the ~igures~ wherein:

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-12- ~ 1 3 ~ ~ 7 g 2 Fig. 1 is a perspective illustration of a test carrier according to the present invention;

Fig. 2 is a section through the test carrier according to Fig. 1 along the line StS;

Fig. 3 is a section corresponding to Fig. 2 but with an alternative layer construction; and Fig. 4 is a perspective illustration of an alternative embodiment of a test carrier according to the present invention.

The test carrier 1 illustrated in Fig. 1 consists essentially of a frame 2 produced, for example, Erom a synthetic resin and a multi-layer test field 2a enclosed in this frame.

The multi-layer test field 2a consists, in the illustrated case, in cross-section, of a laminated composite 3 acting as erythrocyte separation means and a porous support layer 4. The laminated composite 3 includes a first zone 5 arld a second zone 6, as well as a transition region 7 indicated by a broken line, between the zones 5 and 6. The porous support layer 4 faces the blood application side 8 oE the laminated composite 3, whereas the second zone 6 faces the evaluation side 9.

The multi-layer test field 2a can, of course, contain further layers. The illustrated example is especially simply constructed insofar as the first zone 5 and the second zone 6 simultaneously contain the ` -13- ~ ~32~7G2 reagents for the detection reactîon. However, it can also be desirable to separate the functions of ~erythrocyte separation and ~detection reaction and to provide additional layers for the latter, especially on the detection side but possibly also on the blood application side.

For carrying out an analytical determination, a possibly pre-measured amount of blood is applied to the blood application side 8, the test carrier thereby usually being held with this side upwardly. The blood penetrates through the porous carrier layer 4 into the first zo~e 5. Because of the construction according to the present invention of the laminated composite 3, upon further penetration, the erythrocytes remain behind so that no red blood coloured matter enters the second zone 6 which forms the detection æone~ The optical evaluation takes place from the evaluation side 9. Pigment in first 70ne 5 blocks the illumination to such an extent -that it cannot penetrate into the region of the laminated composite 3 in which red blood coloured ; matter is present.

Consequently, the analysis is not falsified by this.

The laminated composite 3 according to the i` present invention thus achieves, in its totality, what is required, for example, in the above-mentioned US-A4 069 817, without appropriate means being stated, namely, filtering off the erythrocytes from the penetrating blood sample and, at the same time, so blocking the ~` - - ~ 132~7~ light illum:ination necessary for the optical evaluation that it does not penetrate into the region of the laminated composite in which red blood coloured matter i9 present.

Details of how the filter action is achi.eved have not been completely elucidated.

On the one hand~ it can be ascertained that a layer having the composition of the first zone 5 (for example applied to a porous support layer) does not have sufficient erythrocyte separating properties. On the other hand, it can be ascertained that a considerable part of the second coating mass, in the case of the forming on the underlying layer, penetrates into thiso Thus, it is to be assumed that the particles of the dispersed or dissolved polymer from the second coatin~ mass penetrate into the previously produced layer, a gradient of the polymer thereby being adjusted in the transition region 7 between the second zone 6 and the first zone 5. It is to be assumed that the comparatively open structure of the first zone 5 is thereby just closed to a sufficient extent that, on the one hand, the erythrocytes are held back but that, on the other hand, even comparatively large components of the sample to be analysed can penetrate into the second zone 6.

Details of the chemical course of the analytical determination are not important for the present invention.

To this extent, it is only important that " ~ 132~7~2 the optically detectable change characteristic for the concentration to be determined takes place in the second zone 6 or in a Eurther layer of the test carrier arranged ~n the same side of the transition region 7 and not in the first zone 5. In the case of numerous test processes usual in clinical chemistry, as concluding step there is formed, for example, a coloured substance ~for example from a chromogenic substrate of an enzyme participating in the reaction) or a coloured substance is so reacted that it changes its colour. Such a reaction co~ponent can be designated "an optically detectable signal-producing component" or briefly also a signal-producing component (SPC).

Such a component is preferably present in the second zone 6 of the laminated composite 3. It is preferably contained in the second coating mass. However, it is also possible subsequently to impregnate or spray the second zone 6 ~ith an SPC, this being especially preferred when the second coating mass is produced from a dissolved organic film former.

However, the SPC must not necessarily be present initially in the second zone 6. On the contrary, it is known to carry out tests in which such components are formed or are present in another layer of a multi-layer test carrier and, in the course of the reaction, pass into the actual detection region. The present inven~ion is also applicable to such processes, in which the - i ~ ~ 132~7~ -16 components can initially be contained in the first zone 5, in the porous support layer ~ or in a further layer arranged in front.

In detail, the laminated composite according to the present invention is preferably produced in such a manner that the first coating mass is Eirst applied to a slowly moving strip oE a material appropriate as porous support layer 4 over the full breadth of the strip. The coating mass thereby has a somewhat honeylike viscosity so that it remains preponderantly on oneside of the textile support layer material but sinks into the intermediate spaces between its preferably multifilar threads. In the case of the finished product 9 from the direction of the blood application side, the material o~ the first zone is to be recognised in the intermediate spaces of the textile struc~ure but it should not completely envelop the threads thereof.

The connection between the support layer and the coating forming the first zone is so firm that it cannot be separated without destruction.

The greater is the proportion of pigment in the first coating mass, the better are the erythrocytes retained but also the more slowly the plasma penetrates into ~he evaluation zone. In the first coating mass, the kieselguhr and the pigment are preferably in a weight ratio of 1:0.5 to 1:2 and especially preferably in a weight ratio of 1:0.8 to 1:1. A corresponding .. . . ...

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-17-~` ~32~7~2 weight ratio is then, of course, also obtained in the first zone 5. In this regard, it is to be noted that all concentration stateMents of the zones 5 and 6 refer to the parts thereoE lying outside of the transition region 7.

The kieselguhr and the polymeric Eilm former in the first coating mass and consequently also in the first zone 5 are preferably in a weight ratio of 1:0.2 to 1:0.9 to one another.

lU After the application of the first coating mass, this is formed to give a thin layer Preferably a socalled "rake", i.e. a doctor blade, is arranged over the transported strip of porous support layer in order to adjust the desired layer thickness.

Correspondingly, in a second working step, which is preferably completely separate frorn the first one because of the necessarily comparatively long drying times, on to the composite of porous support layer and the layer arranged thereon from the first coating mass, there is applied the second coating mass in corresponding manner. This second layer should be applied very thinly. The more polymer is applied, the more strongly .

are the erythrocytes held back. At the same time, however, a slower formation of the optical signal is to be observed. The polymeric film former in the second coating mass is preferably applied with a maximum weight per unit surface area of 200 g./m~, preferably 100 g./m2.

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~18- ~ 3 ~ ~ 7 ~ 2 As mentioned above, in practice it has been shown that the second coating mass penetrates to a considerable extent into the underlying layer.

Thus, for example, in the case of an adjusted height o~ the coating gap of 5 10 ~, a consumption of second coating mass was found which corresponds to a layer of 50 ~ thickness.

As men~ioned above, the laminated composite 3 can also be produced, for example, on a glass plat~ from which it can easily be removed after the production.

10 Since, however, it is not mechanically stable, it is preferable to apply it to a support material.

Fig.3 shows an alternative embodiment of a test carrier according to the present invention in which, as support material, a transparent film 10 is used which is stuck 15 to the second zone 6.

Such an embodiment can be prefer able in cases in which the porous support layer 4 would disturb.

The laminated composite according to the present invention can be used in test carriers of greatly 20 differing external construction.

All that is important is that the blood is supplied to the first zone 5 and that the evaluation takes place on the side of the second zone 6.

Otherwise, however, numerous further constructional features, 25 layers or reagents can be used. 0 Fig. 4 shows, for example, a test carrier 11 formed similarly to a conventional test strip with a ` . ' : `,. ~-,, `~ " ' . ` ` ' ;

.

` - ~ 132~7~2 --19- narrow, longitudinally extending base filM 12 wllich serves for handling.

On the base EilM 12 is to be seen a test zone 13 in which a liquid transport layer 1~ is stuck, for example, with a melt adhesive strip 15 to the base film 12. The liquid transport layer 14 lS partly covered over by a test field 16 which, in cross-section, is constructed corresponding to test field 2a in Fig.2.

With the porous support layer 4 downwardly, it is so fixed by means of the melt adhesive strip 15 to the base film 12 that it is in liquid contact with the liquid transport layer 14.

In the case of the test carrier illustrated in Fig. 4, the blood sample is applied to the partial region 13a of the liquid transport layer not overlapped by the laminated composite 16 and penetrates from there into the liquid transport layer (by the ac~ion of capillary force) in the region under the composite laminate 16 so that the blood can penetrate into the first zone of this laminated composite 16.

The construction illustrated in Fig. 4 has the advantage that the blood application and the evaluation take place from the sarne test carrier side.

The invention is used especially advantageously in coMbination with the test carrier construction described in ~.S.

Patent 5,104,811.

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~ 3 2 ~ 7 ~ 2 -2n The following Examples are given for the purpose of illustrating the present invention:

Example 1.

P oduction of a test fielcl for a test carrier for the detec~7on of glucose in blood.

198 g. acrylic acid ester co-polymer dispersion (Acronal*14D of BASF, Ludwigshafen, Federal ~epublic of Germany, 55% in water) 174 g. swollen, highly viscous methylhydroxyethylcellulose (0.5% in water) 336 g. kieselguhr 336 g. titanium dioxide 0.~5 g. tetraethylammonium perfluorooctanesulphonate 40 g. 0.5M phosphate buffer, pH 5.5 23 g. methanol 46 g. l-hexanol 6~ g. acetone 65 g. water - are worked up to give a homogeneous first coating mass and coated on to a 0.20 mm. thick polyester filter fabric (2 F 777, Schweizer Seidengazefabrik Thal, Switzerland) with 0.18 mm. gap height and dried.

On to the so obtained coated carrier is applied a second coating mass consisting of 102 g. acrylic acid ester co-polymer dispersion (Acronal 14D of BASF, 55% in water) 38 g. swollen, highly viscous methylhydroxyethyl cellulose (0.5% in water) *-trade mark -21- 1 ~2 ~ ~ ~ 2 3 g. sodium dodecylbenzenesulphonate 36 KU glucose oxidase 1050 KU peroxidase 1.48 g. 3,3',5,5'-tetramethylbenzidine 0.53 g. l-phenylsemicarbazide 28 g. 1-methoxy-2-propanol 40 g. l-hexanol 38 g. water which had been worked up to a homogeneous mass, with 0.02 mm. gap height and dried.

The so obtained laminated composite is used in a test strip according to Fig. 4 and gives a good gradation in the concentration range of 20 - 250 mg.

glucose/dl. in the case oE the use of whole blood.

Example 2.

Production of a test field for a test carrier for the detection of triglycerides in blood.

37 g. polyvinyl propionate dispersion ~50% in water) 29 g. swollen, highly viscous methylhydroxyethyl cellulose (0.5% in water) 56 g. kieselguhr 56 g. titanium dioxide 3.2 g. sodium dodecylbenzenesulphonate 40 g. 0.5M phosphate buffer, pH 5.5 3.8 g. methanol 7.7 g. l-hexanol 11.5 g. acetone 22 g. water .

- .

` -22- '~" 132~7~ are worked up to give a homogeneous first coating mass and coated with 0.15 mm. gap height on to a 0.09 mm.

thick pure silk Eabric (Type 541 oE the Spinnhutte Seidentechnik9 Celle, Federal Republic oE Germany) and dried.

To the so obtained carrier is applied a second coating mass, consisting of 20 g. polyvinyl propionate dispersion (50% in water) 0.28 g~ sodium alginate 70 g. 0.2M phosphate buffer, pH 7.5 0.58 g. adenosine-5'-triphosphate, disodium salt 0.59 g. magnesium sulphate heptahydrate 1.0 g. dioctyl sodium sulphosuccinate 0.45 g. 3,3',5,5'-tetramethylbenzidine 15 mg. 1-(4-methylphenyl)-semicarbazide 16.4 g. l-hexanol 30 g. acetone 2.0 g.

Triton*X-100 27 KIJ cholesterol esterase 20 8.0 KU glycerol phosphate oxidase ~t 27 KU glycerokinase 73 KU peroxidase 50 g. water, which had been worked up to a homogeneous mass and the pH of which had been adjusted to 7.5, with 0.01 mm.

gap height and dried.

A~ter dropping blood on to the fabric side, the *trade mark ~ ' ' " , ~ , '' - ' ' ' .

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~ ~3257~2 -23 test ields so obtained give a good gradation in the concentratiotl range oE 100 - 300 mg. tri~lyceride/dl.

Exatl1ple 3.

Production of a test field for a test carrier Eor .. _ . . . ..

the detection oE glucose in blood.

To 46.3 g. of a 20% by weight solution of polyvinyl acetate (Mowilith*70 of the Eirm Hochst AG) in acetone/ l-hexanolJmethanol ~3:Z:l, v/v/v) is added a solut:ion of 1.30 g. dioctyl sodium sulphosuccinate in 29.4 g.

acetone. 28 g. kieselguhr and 28 g. titanium dioxide are dispersed in tllis mlxture. With this homogeneous first coating Mass, a 0.20 mm. thick polyester filter fabric (2 F 777, Schweizer Seidengazefabrik Thal, Switzerland) is coated with a gap height of 0.2 mm.

and dried.

On to the so obtained coated carrier is applied a second coating mass consisting of 64 g. of a 20% weight solu~ion of polyvinyl acetate tMowilith 70) in acetone/l-hexanol/methanol (3:2:1 v/v/v) 1.3 g. dioctyl sodium sulphosuccinate 36 g. acetone 264mg. l-phenyl semicarbazide 740 mg. 3,3',5,5'-tetramethylbenzidine 13.8 g. 1-methoxy-2-propanol which had been worked up to give a clear, viscous solution, with a gap height of 0.04 mm. and dried.

~trade mark ... :

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-24- ~ ~32~7~2 On to the so obtained test field can be applied the reagents a) by a further coating or the reagents b) by spraying:

a) The coating mass for the coating consists of 20 g. swollen, highly viscous methylhydroxyethyl cellulose (0.5% in water) 36 kU glucose oxidase 1050 kU peroxidase and is applied with a gap height oE 0.02 mm. and dried.

b) The spray solution consists of 72 kU glucose oxidase 2.1 MU peroxidase 40 Ml. water and is sprayed on in an a~nount of 20 - 30 ml./m2 and dried.

Upon dropping blood on to the fabric side, the so obtained test fields give a good gradation in the ,~ concentration range of 150 - 600 mg. glucose/dl.

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~ 132~7~2 -25 Suitably the first coating mass, when applied to the porous substrate, has a v;scosity of 300 to 3,000 mPas (millipascal seconds) with a shear gradient of 492 s 1 according to DIN 53019; and the second coating mass, when applied to the dry layer formed from the first mass, has a viscosity of 100 to 1,000 mPas with a shear gradient of 492 saccording to DIN 53019.