Process for the production of porous membranes, the membranes produced thereby and their use as supporting matrices in test strips

The present invention relates to a process for the production of porous, and particularly macroporous, membranes. The membranes produced by the process are highly absorbent and can therefore be employed, as supporting matrices for test strips. These test strips can be used for the detection of substances to be analyzed in a liquid.

The present invention relates to a process for the production of porous, 
and particularly macroporous, membranes. The membranes produced by means 
of the process are highly absorbent and can therefore be employed, in 
particular, as supporting matrices for test strips. These test strips can 
be used for the detection of substances to be analysed in a liquid, in 
particular urine. 
The determination of a component of a liquid by means of dry chemical 
detection units, also known as test strips, is one of the established 
methods in clinical diagnostics. Thus, the detection of certain components 
of urine or blood, such as glucose, protein, bilirubin, ketones, 
cholesterol or enzymes, is carried out by means of test strips to an 
increasing extent. Diagnosis test strips are also used to an increasing 
extent by nonprofessional persons, so that it is of great importance that 
handling should be as reliable and simple as possible. 
A frequent source of error in the handling of diagnosis test strips is 
nonuniform wetting with the test liquid after being dipped into the 
sample. Drops of liquid remaining on the test area result in a nonuniform 
colour change ("drop problem"). As explained in greater detail in EP-A 
64,710, increased or decreased concentrations of substance can be 
simulated by this means. In addition, in the case of multiple test strips, 
transfer of reagents of adjacent reagent zones can result between 
different test areas through the formation of liquid bridges ("run-over 
problem"). 
Admittedly, if absorbent paper is used as the matrix material, the problem 
of supernatent test liquid is largely solved owing to the great absorbency 
of the paper used. However, paper has other substantial disadvantages, 
such as, for example, inhomogeneous surface, varying composition and 
mechanical instability. 
Attempts to solve the drop problem are described in German 
Offenlegungsschrift (German Published Specification) 2,118,455 and in 
German Offenlegungsschrift (German Published Specification) 2,854,342. In 
these texts, paper which has been rendered water-repellent and which can 
absorb residues of liquid via the hydrophilic cut edge is used. The paper 
which has been rendered water-repellent is mounted below the reagent 
matrix, so that two-layer systems are involved. 
Owing to the problems relating to the mechanical stability and also the 
inhomogeneous surface in paper, thin polymer films are preferred to an 
increasing extent in recent times as reagent supports which do not have 
these disadvantages. Test strips having a uniform surface condition are 
very important, in particular for reflectrometric evaluations. Test strips 
of this kind have been described, for example, in German Patent 
Specification 1,598,153 and German Offenlegungsschrift (German Published 
Specification) 2,332,760. 
The test strips described in the patent specification first mentioned are 
so designed that an excess of sample is applied and is removed by wiping 
off after a definite time. In the second patent specification, the sample 
is fed in via a hydrophilic, microporous polymer layer and is passed on 
from there into the layer of reagent below. 
However, as explained in greater detail in EP-A 64,710, both systems are 
not suitable for analyses via the dip and read method. 
Other systems of test strips in which the polymer matrices consist of 
microporous polymer membranes having an asymmetric structural design are 
described in German Offenlegungsschrift (German Published Specification) 
3,407,359. The pores at the surface of the matrix are so constituted that, 
when whole blood is applied, the blood serum penetrates into the polymer 
matrix and initiates the detection reaction. The red blood cells, however, 
remain on the surface of the membrane and are removed by wiping off. 
If test strips produced on the basis of polymers, such as are described in 
German Patent Specification 1,598,153 or German Offenlegungsschrift 
(German Published Specification) 3,407,359 are dipped into test liquids, 
such as, for example, urine, this results, in contrast with paper test 
strips, in a nonuniform colour change of the surface of the test strip 
after the latter has been taken out of the test liquid. Nor can this 
disadvantage be eliminated by lightly tapping and wiping the test strip on 
the wall of the sample vessel. The cause of the inhomogeneous colour 
reaction is nonuniform wetting of the surface of the plastic and the very 
low absorbency of these matrices. Only by wiping off the excess of sample, 
as is prescribed, for example, when these test strips are used for the 
analysis of whole blood, can homogeneous colour reactions be produced. 
Handling in this manner is, however, disadvantageous and unusual in the 
case of urine test strips, for obvious reasons. 
The object of the present invention was, therefore, to develop a test strip 
which is based on plastics and which can be handled with similar 
simplicity to reagent strips made of paper, but which at the same time has 
the advantages of film strips made of synthetic plastic, that is to say 
exhibits small variations in respect of surface condition, chemical 
structure and layer thickness and better mechanical stability. 
Developments having a similar objective are described in EP-A 64,710. 
Multilayer test agents are suggested in that text for solving the problem, 
which consist of a support, a layer fastened thereto which absorbs the 
liquid sample in a delayed manner, a polymeric layer of reagent fastened 
on top of the latter and a network layer made of polymer fabric covering 
the latter. Excess amounts of liquid sample are transported by the 
covering network layer (fine-meshed polymer fabric) into the absorbent 
layer (paper which has been rendered water-repellent) located under the 
reagent layer and are there absorbed via the cut edges. 
A further function of the polymeric network is to compensate for the 
disadvantageous properties mentioned above of the polymeric layer of 
reagent in respect of uniform wetting and absorbency, by holding, as a 
result of the polymer network, a fine film of liquid on the surface of the 
reagent layer, which slowly diffuses in or evaporates. 
The test units described in EP-A 64,710 exhibit an advance compared with 
the conventional paper test strips in respect of surface condition, but 
disadvantageous effects occur in the test reaction which are due, in 
particular, to the complicated, multilayer construction. 
Thus the reaction colour changes after the test as a function of the time 
because initially a film of liquid remains adhering in the polymer network 
and this dries out slowly. As a result, more intensive colours can be 
observed immediately after the test reaction and these become paler as 
drying increases and are then affected by the reflection properties of the 
polymer network. 
A network structure of the polymer fabric can also lead to the formation of 
irregular colour zones, particularly at low analytical concentrations. The 
reason for this is that points in the reaction zone which are in direct 
contact with the polymer fabric exhibit more intense colour changes, since 
a different penetration or evaporation behaviour of the test liquid exists 
here than at points on the surface of the reagent, which is not subject to 
direct contact with the polymer fabric. 
Complications can also result in the systems described in EP-A 64,710 if 
two adjacent test zones, for example for a low and a high range of glucose 
(for example Diabur test 5000.RTM.), is fixed to a test strip by means of 
a common polymer network. Thus, particularly in the case of samples having 
low concentrations of glucose, which in themselves ought only to initiate 
a colour reaction with the low range test area, colour changes are 
sometimes also observed, particularly in the boundary region of the high 
range field. The reason for this is the formation of liquid bridges 
between the polymer fabric and the boundary region of the reaction zone. 
When the supernatent test liquid evaporates, the result is a concentration 
of the substance to be determined by analysis in this region and hence the 
formation of increased intensities of colour. 
The present invention therefore relates to a new process for the production 
of porous, and particularly macroporous, polymer membranes. 
These membranes consist essentially of at least two polymers which are 
incompatible in solution, that is to say result in phase separation in a 
common solution. Further details on segregating, incompatible polymer 
systems can be obtained from the literature (see Paul J. Flory, Principles 
of Polymer Chemistry, Ithaca, N.Y. 1953). By dispersing insoluble fillers 
into this unstable solution, the latter is converted into a stable, 
homogeneous dispersion. This dispersion is then applied to a substrate as 
a casting solution. A membrane is produced from this casting solution by 
precipitation coagulation, also known as phase inversion. 
Information on the fundamental principles of this technology are given by, 
for example, H. Strathmann, "Trennungen von molekularen Mischungen mit 
Hilfe synthetischer Membranen" (the Separation of Molecular Mixtures by 
means of Synthetic Membranes), Steinkopfverlag, Darmstadt (1979) and D. R. 
Lloyd "Materials Science of Synthetic Membranes", ACS Symp. Ser. 269, 
Washington, D.C. (1985). 
The typical membrane structures which are obtained in precipitation 
coagulation are also described in these publications. These are always 
asymmetric membrane structures having an impervious polymer skin on the 
membrane surface and a fairly high porosity in the interior of the 
membrane. The pore structure can be finger-like or foam-like, depending on 
the formulation of the casting solution. As a result of the impervious 
polymer skin at the surface of the membrane, the pore diameters of 
conventional membranes are limited and do not, as a rule, exceed values of 
approximately 8-10 .mu.m. Membranes of this type show no absorbency 
comparable with that of paper, such as the membranes of the present 
invention have. 
Furthermore, it is known that polymer casting solutions used for the 
production of precipitation coagulation membranes must be homogeneous, 
since otherwise unstable membranes are obtained. For this reason, typical 
membrane casting solutions consist of a polymer and a solvent or mixture 
of solvents (for example polyamide in dimethylacetamide or cellulose 
acetate in acetone/formamide). 
Attempts have already been made to produce membranes of increased 
permeability by means of special formulations of the polymer casting 
solutions. Thus membranes are described in Chem. Pro. Res. Dev. 22 (1983) 
pages 320-326 or in German Offenlegungsschrift (German Published 
Specification) 3,149,976 for the production of which polymer casting 
solutions have been employed containing water-soluble polymers, for 
example polyvinylpyrolidone, which are dissolved out in the course of the 
coagulation in water and thus result in enlarged pores. 
Membranes composed of mixtures of polymers are also described. The 
formulations of the corresponding casting solutions are, however, composed 
in such a way that, by virtue of the solubility parameters, homogeneous 
polymer solutions are obtained. For example, membranes composed of a 
mixture of cellulose acetate and polymethyl methacrylate are described 
EP-A 66,408, which have an increased permeability compared with the 
conventional membranes composed of one polymer. In this case, however, one 
is dependent on polymer combinations having similar solubility parameters 
and on specific, very narrow mixing ratios. Although membranes of this 
type have increased porosity, they still do not have the powerful 
absorbency peculiar to the membranes according to the invention or uniform 
wetting with the test liquid. 
It has now been found, entirely surprisingly, that membrane matrices 
composed of synthetic polymers having a powerful absorbency and a uniform 
wettability with liquids can be produced by using, for the production of 
the membrane, casting solutions composed of mixtures of polymers in 
combination with certain fillers. 
This is because it has been found, surprisingly, that polymers which in 
themselves are incompatible and immiscible in any mixing ratio whatever 
can be converted into homogeneous casting solutions if certain insoluble 
fillers are dispersed into them. 
If, for example, a 20% strength by weight solution of polyurethane in 
dimethylformamide (PU/DMF solution) and a 20% strength by weight solution 
of polyacrylonitrile in dimethylformamide (PAN/DMF solution) are mixed 
with stirring, phase separation takes place after standing for a short 
time. Mixtures of this type are unstable and are unsuitable as casting 
solutions for the production of membranes. 
If, on the other hand, the same polymer/DMF solutions are combined with the 
simultaneous or subsequent dispersions of fillers, for example talc, into 
them, homogeneous, stable casting solutions are obtained which are 
suitable for the production of membranes by the method of precipitation 
coagulation. 
Surprisingly, the membranes produced from casting solutions of this type 
have, in comparison with the known membranes, markedly larger pores on the 
surface, a very much higher overall porosity and a markedly increased 
absorbency, which is comparable with that of chromatography paper. 
As shown by the electron microscope photographs of the cross-section of 
these polymer membranes according to the invention, the latter are novel 
structures having a felt-like construction, while the asymmetric 
structural construction with the impervious polymer skin on the membrane 
surface is almost completely repressed. In the case of a membrane of the 
above formulation, pore diameters of up to 30 .mu.m can be discerned on 
the surface of the membrane. 
The polymer casting solutions required for the production of macroporous 
membrane matrices of this type must fulfill the following conditions: 
the solutions of the individual polymer components must not be miscible 
with one another. In the case of miscible systems, microporous membrane 
structures having a pronounced asymmetric structure are obtained 
analogously to conventional casting solutions 
the solvents of the individual polymer components must be miscible with one 
another 
in order to convert the immiscible polymer components into homogeneous 
casting solutions, suitable insoluble fillers, for example inorganic 
fillers, must be dispersed into them. 
The nature of the filler can in some cases be important for the stability 
and homogeneity of the casting solution. Whereas, for example, casting 
solutions composed of polyurethane/polyacrylonitrile mixtures with 
titanium dioxide (TiO.sub.2 RKB.sub.2 .RTM., Bayer AG) or barium sulphate 
(Blanc fixe micronized.RTM., Sachtleben) having specific surface areas of 
approximately 3 m.sup.2 /g (particle sizes approximately 0.5 to 1.0 .mu.m) 
are unstable and inhomogeneous, solutions of the same mixture of polymers 
containing talc (AT 1 talc, Norwegian Talc) have a good homogeneity and 
stability of dispersion. 
It was also possible to obtain similarly good results with very finely 
grained fillers having a large specific surface area, for example Degussa 
P25 titanium dioxide (approximately 40 m.sup.2 /g) or Degussa Aerosil 200 
silicon dioxide (200 m.sup.2 /g). Mixtures of talc with barium sulphate or 
talc with RKB2TiO.sub.2 or Degussa P25 titanium dioxide with barium 
sulphate also result in suitable casting solutions. It was also possible 
to prepare suitable casting solutions by dispersing in microcrystalline 
cellulose (for example Arbocel BE 600/30, J. Rettenmaier & Sohne). Other 
suitable fillers are CaCO.sub.3, MgCO.sub.3, ZnO and iron oxides. 
The nature of the filler employed can also be used to change the colour of 
the reagent matrix, for example by means of coloured iron oxide pigments, 
and to influence the reflection properties of the reagent matrix. 
The function and action of the filler is the conversion of the unstable, 
inhomogeneous polymer solution into stable and homogeneous casting 
solutions. The mechanism of this "solubilization" is not known. 
The pore size can be controlled via the selection of the polymers and the 
amounts of each of them. The fillers have virtually no affect on the pore 
size. The particle diameter of the fillers are within a much smaller order 
of magnitude than the pore diameters of the polymer membrane. A process of 
precipitation coagulation in combination with the type of casting 
solutions described here is responsible for the formation of the pores of 
the membranes according to the invention. 
For example, "binary polymer mixtures" consisting of the following classes 
of polymers with talc as filler were prepared in order to produce the 
macroporous membrane matrices according to the invention: 
Cellulose esters/polyvinyl esters 
Polyurethane/polyacrylic derivatives or acrylic copolymers 
Polycarbonate copolymers/polyurethane 
Polyvinyl derivatives/polysulphones 
Polyamides or polyimides/polystyrene or styrene copolymers 
Polyparadimethylphenylene oxide/polyvinylidene fluoride. 
Other combinations within these binary polymer systems and ternary polymer 
mixtures were also employed to produce the membranes according to the 
invention. 
Preferred polymer combinations are described in the following examples 
(also containing talc as the filler): 
Cellulose acetate (Cellidor CP.RTM.)/polyvinyl acetate (Mowilith.RTM.) 
Poyurethane (Desmoderm KBH.RTM.)/polyacrylonitrile (Dralon T.RTM.) 
Desmoderm KBH.RTM./amine-modified Dralon (Dralon A.RTM.) 
Desmoderm KBH.RTM./anionically modified Dralon (Dralon U.RTM.) 
Polysulphone (Udel P 1700.RTM.)/polyvinylidene fluoride 
Polyether-polycarbonate/Desmoderm KBH.RTM. 
Dralon U.RTM./Mowilith.RTM. 
Cellidor CP/Dralon U.RTM. 
Cellidor CP.RTM./Dralon U.RTM./polystyrene 
Mowilith.RTM./Desmoderm KBH.RTM./polyvinyl chloride 
The ratio of the polymers in each particular combination required for the 
phase separation can be determined by suitable tests. 
The following ternary polymer system is very particularly preferred for the 
production of the macroporous membrane matrices according to the 
invention: 
Desmoderm KBH.RTM./Mowilith.RTM./Dralon T.RTM., it being also possible for 
Dralon T.RTM. to be replaced by Dralon A.RTM. or Dralon U.RTM.. 
The chemical structures of the polymers employed preferentially are 
described in the appendix. 
Dimethylformamide (DMF) is very suitable as a solvent for the preparation 
of the particularly preferred polymer casting solutions. Other suitable 
solvents which should be mentioned, depending on the polymers used, are 
N-methylpyrrolidone (NMP), dimethyl sulphoxide (DMSO), dimethylacetamide, 
dioxolane, dioxane, acetone, methyl ethyl ketone or Cellosolve.RTM.. 
The whole process of producing membranes can be described in terms of the 
particularly preferred example as follows: the polymer solutions, in each 
case approximately 20% strength by weight in DMF, of Desmoderm KBH.RTM., 
Mowilith.RTM. and Dralon.RTM. were mixed to give a homogeneous polymer 
casting solution by means of a high-speed stirrer (Dissolver), while talc 
was dispersed into the mixture. After it had been degassed in vacuo, the 
casting solution was applied to a supporting substrate in a layer 
thickness of 150 .mu.m by means of a doctor-blade, and was dipped into the 
coagulation bath, preferably pure water. After a dwell time of 
approximately 2 minutes, the polymer membrane thus formed was taken out of 
the coagulation bath and dried by means of hot air. 
As well as talc (Norwegian Talc AT 1), the following fillers have proved 
suitable in the particularly preferred ternary polymer mixture mentioned 
above: microcrystalline cellulose (Arobocel BE 600/30, J. Rettenmaier & 
Sohne), zeolites, bentonites and fillers having a specific surface area of 
more than 10 m.sup.2 /g (for example Degussa P 25 titanium dioxide or 
Degussa Aerosil 200 silicon oxide) and also mixtures of fillers such as, 
for example, titanium dioxide (Degussa P 25) and barium sulphate 
(Sachtleben Blanc fixe micronized), mixtures of talc and titanium dioxide 
(Bayer AG RKB2), a mixture of titanium dioxide having a greater and 
smaller specific surface area (for example Bayer AG RKB2 TiO.sub.2 
/Degussa P25 TiO.sub.2) or talc and barium sulphate (Blanc fixe 
micronized), which has proved very particularly suitable. 
Other components which can also be employed concomitantly in the casting 
solution for the production of the macroporous membranes are surfactants, 
for example dioctyl sodium sulfosuccinate or dodecylbenzenesulphonate. 
Surfactants of this type act primarily to stabilize the reaction colours 
which are formed during the detection reaction. Water-soluble polymers, 
such as cellulose ethers, polyethylene glycols, polyvinyl alcohol or 
polyvinylpyrrolidone can also be a constituent of the polymer casting 
solution. Other suitable additives are so-called coagulation auxiliaries, 
such as, for example, cationic polyurethane dispersions (Desmoderm 
Koagulant KPK.RTM.). 
The support substrates used for coating can differ, depending on the 
desired end use. In the production of support-free membranes it is 
possible to employ, for example, glass or silicone-treated support 
materials. If the objective is use as a flat membrane, support materials 
which are permeable to liquids, such as polymer fabrics or polymer 
non-wovens on which the polymer membrane exhibits a good adhesion, are 
employed. 
If porous polymer matrices (membranes) having precisely defined porosities 
(precise layer thicknesses having a constant liquid absorption) are to be 
produced, such as are required by the polymer matrices according to the 
invention for diagnosis test strips, it is preferable to employ smooth 
films, impermeable to liquids, as the support substrate. Polymer films 
consisting of, for example, polyethylene terephthalate, polycarbonate, 
cellulose esters, polyethylene, polyamide or other thermoplastic polymers 
or polymer blends are preferred. Particularly preferred polymer films are 
composed of polyethylene terephthalate, for example Hostaphan.RTM. films 
made by Hoechst. The polymer films can, if appropriate, be provided with 
adhesive layers or antistatic materials. 
The process according to the invention makes it possible to produce 
membranes having a very good porosity which can be adapted to suit a 
particular use. The process is particularly suitable for the production of 
macroporous membranes. In this context, macroporous denotes an average 
pore diameter greater than 10 .mu.m at the membrane surface. Average pore 
diameters of 10 to 50 .mu.m are preferred, and those of 10 to 30 .mu.m are 
very particularly preferred. 
Owing to the good absorption properties, one of the main fields of use for 
the membranes of the present invention is their use in the production of 
test strips which can be used in diagnostics. The good absorption 
properties have a particularly advantageous effect in the case of urine 
test strips. 
After such test strips have been dipped into the test liquid and wiped on 
the wall of the test vessel, a uniform colour reaction and a test strip 
surface which, within a short time (usually less than 15-20 seconds) 
appears dry are obtained. In addition, substantially more intense 
colourations result, as well as a better distinguishability over a wider 
range of concentrations, particularly when compared with the test strips 
hitherto known. 
The incorporation of the reagents required for the detection reaction can 
be carried out in various ways, for example by stirring them into the 
casting solution, by subsequently impregnating the porous films or by 
combining these two processes. 
In preferred variants for the incorporation of the reagents, reagents which 
are soluble in organic solvents or insoluble in water are incorporated 
into the polymer casting solution, whereas water-soluble reagents are 
introduced into the dried, porous reagent matrix in a separate 
impregnation stage. 
For example, the preferred incorporation of reagents for the detection of 
glucose is carried out by dissolving in the polymer casting solution 
chromogens of the benzidine type, such as, for example, 
3,3'-5,5'-tetramethylbenzidene (TMB). The casting solution is applied to a 
supporting material (layer thickness approximately 100 to 500 .mu.m) by 
means of a doctor blade, an extrusion caster or another suitable coating 
method, and is coagulated in water. After coagulation, 
chromogen-containing, porous polymer matrices which adhere to the 
supporting material are obtained, and, after drying, these are impregnated 
with the aqueous, buffered enzyme system (glucose oxidase or peroxidase). 
The impregnation is preferably carried out by the extrusion method 
described in EP-A 246,505. 
If appropriate, it is also possible to incorporate in the polymer casting 
solution inert, water-insoluble, organic or inorganic dyestuffs which 
produce coloured membranes after coagulation, so that the corresponding 
mixed colours are formed in the glucose reaction. 
For example, a yellow-coloured membrane matrix which resulted in green 
reaction colours in the glucose reaction using TMB as the chromogen was 
obtained by incorporating the yellow dyestuff Telon Echt Gelb (Bayer AG). 
The macroporous reagent matrices according to the invention can, if 
desired, be combined with other absorbent materials which absorb residues 
of liquid remaining on the lower edge of the test strip after the 
immersion process, so that it is even possible to dispense with tapping 
lightly on the test vessel after immersion. Materials of this type should 
be so constituted that their absorptive capacity is not exhausted or not 
completely exhausted during the immersion process (approximately 1 
second). After the test strip has been taken out of the test liquid, 
excess residues of liquid should, however, be removed completely by 
suction from the reagent area within a short time (approximately 5-10 
seconds). Examples of suitable materials are absorbent paper, the surface 
of which has been modified with layers permeable to water, for example 
layers composed of polyethylene or silicone. As described in German 
Auslegeschrift (German Published Specification) 2,118,455 and German 
Offenlegungsschrift (German Published Specification) 2,854,342, materials 
of this type can absorb residues of liquid via the hydrophilic cut edges. 
These "liquid absorbers" are fixed, in the patent specifications 
mentioned, below the reagent matrix and thus form an element of a 
multi-layer test strip system. 
It has now been found, surprisingly, that, in order to solve the drop 
problem, in the macroporous reagent test strips according to the 
invention, the drop absorbers can be advantageously fixed immediately next 
to the reagent test area, so that, in contrast with the systems known 
hitherto, a single-layer test strip assembly is possible. As shown in FIG. 
1, several test areas (2) can also be combined on one support (1) with, if 
desired, several drop absorbers (3). Since, in the preferred single-layer 
assembly, the surface of the drop absorber is also available, in contrast 
with the two-layer assembly, it has furthermore been found that additional 
advantages can be achieved if the surface of the drop absorber is also 
permeable to liquids. In this regard, as already described, the absorption 
of liquid must take place in such a way that the absorptive capacity is 
not yet exhausted during the immersion process, but develops its 
absorptive action only after the test strip has been taken out of the test 
liquid. It has now been found, surprisingly, that certain polymer 
nonwovens such as are employed, for example, in filtration in the milk 
industry, display properties of this type. Examples of suitable "drop 
absorbers" are cellulose nonwovens for the filtration of milk, for example 
of the FFM 2687 type made by Freudenberg. The delayed absorption behaviour 
can be observed in nonwoven materials of this type when they are fed with 
water, aqueous solutions or urine. 
As has been found further, it is also possible to establish a delayed 
absorption behaviour with materials which absorb strongly and fast, by 
coating the surface of these materials with certain polymer solutions or, 
preferably, with aqueous polymer dispersions. For example, it is possible 
to prepare materials having the required properties of delayed absorption 
via the coated surface from strongly absorbent paper, nonwovens or polymer 
fabrics which in themselves are not immediately suitable as drop 
absorbers, by coating these with aqueous polymer dispersions, preferably 
ionic polyurethane dispersions. Similar effects can be achieved if 
strongly absorbent materials are provided, on the surface, with fine-mesh 
polymer fabrics (for example Nybolt PA 15/10.RTM. polyamide fabric, 
Schweizer Seidengazefabrik AG, Zurich). 
If the porous reagent materials corresponding to FIG. 1 are fixed, together 
with the drop absorbers described, on a test strip mounting and are 
immersed in aqueous test solutions, test strips are obtained a few seconds 
after withdrawal in which the reagent area no longer exhibits any 
supernatant film of liquid on its surface and in which the drop absorber 
also appears dry on the surface a few seconds (approximately 10 seconds) 
later. 
The absorption property of the drop absorber can, as already mentioned, be 
established by coating it with, preferably, aqueous polymer dispersions. 
If appropriate, it is possible to add to the polymer dispersions fillers, 
such as SiO.sub.2 (Degussa Aerosil 200) or titanium dioxide (Degussa P 25 
or Bayer AG RKB2), the ratio by weight of aqueous dispersion to filler 
being within the range of 0.01-0.5. 
Another suitable possible means of arranging the drop absorber and the 
reagent area arises by combining the techniques described in the two 
Offenlegungsschriften (German Published Specification) German 
Offenlegungsschrift 3,520,847 and German Offenlegungsschrift 2,854,342. 
The test strips were produced by cutting the macroporous reagent matrices 
or the "drop absorber of delayed absorbency of liquid" according to the 
invention into pieces about 5.times.5 mm in size and glueing them, in 
accordance with FIG. 1, onto polystyrene test strip mountings 
(Tricyte.RTM. 5 mm.times.80 mm) by means of double-sided adhesive tape. It 
is also possible for the macroporous reagent matrices according to the 
invention to be applied, as though as "zones", to an adhesive mounting 
directly by means of the coagulation process and for the drop absorber 
then to be fastened in the interspaces between these "zones". Other 
arrangements for the reagent matrix and the drop absorber are also 
conceivable, however.

The production of the macroporous reagent matrices, various detection 
reactions by means of these matrices, the production of drop absorbers and 
the combination of the latter with the test strips according to the 
invention are described in the following examples. 
EXAMPLE 1 
The Production of a Urine-Glucose Test Strip 
a) Production of the macroporous membrane matrix 
21.6 g of a 17 per cent strength Dralon U/DMF solution, 
65.2 g of a 20 per cent strength polyurethane (KBH)/DMF solution, 
86.6 g of a 25 per cent strength Mowilith 50/DMF solution, 
22.5 g of sodium dioctyl sulphosuccinate, 
14.8 g of AT 1 talc, 
59.4 g of barium sulphate (Blanc fixe micronized), 
17.3 g of a cationic polyurethane dispersion (Bayer AG KPK) and 
140.0 g of dimethylformamide 
are processed by means of a high-speed stirrer (Dissolver) to give a 
homogeneous dispersion. After being degassed in vacuo, this casting 
solution was applied, by means of a doctor knife, as a coating of layer 
thickness 150 .mu.m to a polyethylene terephthalate film (PET, 
Hostaphan.RTM.) 200 .mu.m thick, and was coagulated in water at 45.degree. 
C. for 3 minutes. The polymer matrix thus formed, which adhered to the 
supporting film, was dried by means of hot air. 
b) Impregnation with reagent solution 
______________________________________ 
Impregnation solution 
______________________________________ 
4-Aminoantipyrine 1 mmol/l 
Na salt of 3,5-dichloro-2-hydroxy- 
10 mmol/l 
benzenesulphonic acid 
Triton X 100 100 mg/l 
Glucose oxidase 40 Ku/l 
Peroxidase in a phosphate buffer 
5 kU/l 
(0.2 m, pH 5.5) 
______________________________________ 
The impregnation of the supporting membrane produced in a) was carried out 
in preliminary tests by immersion for a short time and subsequently drying 
by means of a hot air dryer. 
Impregnation under production conditions was carried out by means of an 
extrusion caster. 
For testing, test strips which were immersed in aqueous glucose solution of 
increasing glucose concentrations (0, 100, 250, 500, 1,000, 2,000 and 
3,000 mg/dl) and then tapped lightly on the wall of the test vessel were 
produced. For an extended test, the aqueous solutions were replaced by 
urine. 
Results: 
The surface of the test strips was free from excess residues of liquid 
after approximately 5 seconds. Homogeneous red colourations were formed, 
which exhibited an increasing intensity, corresponding to the increasing 
glucose concentrations, a colour gradation being recognizable up to 1,000 
mg/dl of glucose. 
EXAMPLE 2 
Production of a Urine-Glucose Test Strip (Chromogen in the Casting 
Solution) 
a) Production of a macroporous, chromogen-containing membrane matrix 
12.0 g of 3,3'-5,5'-tetramethylenebenzidine (TMB) were additionally added 
to the formulation listed in Example 1a. The chromogen-containing casting 
solution was processed further as in Example 1, and a colourless, 
TMB-containing membrane, adhering to a PET film, was obtained. This 
membrane was impregnated analogously to Example 1b, using the following 
impregnation formulation. 
b) impregnation with the enzyme solution: 
43 KU of GOD, 
100 KU of POD, and 
0.2 g of Triton X 100 
in 100 ml of citrate buffer (0.2 mM, pH 5.5) 
Results of test: 
After the test strips had been immersed in the test solutions and briefly 
tapped lightly on the test vessel, reagent areas which were free from 
liquid were obtained after approximately 5 seconds, and these exhibited 
blue colourations of increasing intensity, corresponding to the increasing 
glucose concentrations. In this regard, a distinct colour gradation could 
be observed up to 2,000 mg/dl of glucose. 
EXAMPLE 3 
Production of a Urine-Glucose Test Strip with a Yellow Background Dyestuff 
12.0 g of TMB and also 0.2 g of a yellow, water-insoluble dyestuff (Bayer 
AG Telon Echt Gelb.RTM.) were additionally added, to the casting solution 
described in Example 1. Further processing and impregnation is carried out 
as in Example 2. Yellow reagent matrices which resulted in green reaction 
colours in the detection of glucose were obtained. As in Example 2, colour 
gradations up to 2,000 mg/dl of glucose could be differentiated. 
EXAMPLE 4 
Production of a Urine-Glucose Test Strip Having a Drop Absorber 
A nonwoven made by Freudenberg under the name FFM 2687 was used as the 
material for the "drop absorber". This is a cellulose nonwoven having a 
synthetic resin polymer as binder. When fed with a drop of water, this 
nonwoven exhibits a delayed absorption behaviour. The drop stands on the 
surface for approximately 5 seconds and later penetrates into the nonwoven 
material. A diagnosis test strip corresponding to FIG. 1 was prepared, the 
drop absorber being fixed on the lower edge of the test strip mounting by 
means of a double-sided adhesive tape. 
The test strip was immersed in urine standard solutions containing glucose 
and, without being tapped slightly on the wall of the test vessel, was 
laid horizontally on the laboratory table. A few seconds later the surface 
of the reagent matrix was free from liquid and that of the drop absorber 
was in turn also free from liquid a few seconds later. A homogeneous 
colouration had been formed on the reagent area. 
EXAMPLE 5 
Production of Drop Absorbers 
A Freudenberg nonwoven (FFM 2695) which absorbed very strongly and rapidly 
was employed as the drop absorber analogously to Example 4. After being 
tested in urine, supernatant test liquid was detected both on the reagent 
area and on the drop absorber, and this could only be removed by tapping 
slightly on the test vessel. The abovementioned nonwoven was accordingly 
unsuitable for use as a drop absorber. 
The required properties of delayed absorption could, however, be 
established by coating this rapidly absorbing nonwoven with an aqueous 
polymer dispersion, followed by drying. The aqueous dispersion was an 
anionic polyurethane dispersion (Bayer AG DLN.RTM.). The wet coating 
amounted to 50 .mu.m and the subsequent drying was carried out in a 
circulating air drying cabinet at 70.degree. C. 
The diagnosis test strips produced in accordance with FIG. 1 were free from 
supernatant test liquid approximately 10-15 seconds after being immersed 
in urine. 
EXAMPLE 6 
Production of Test Strips for the Detection of Protein 
a) Preparation of the macroporous membrane matrix 
The casting solution of the following formulation: 
21.6 g of a 17 percent strength Dralon U/DMF solution, 
65.2 g of a 20 percent strength polyurethane (KBH)/DMF solution, 
86.6 g of a 25 percent strength Mowilith 50/DMF solution, 
22.5 g of sodium dioctyl sulphosuccinate, 
140.0 g of dimethylformamide, 
14.8 g of titanium dioxide (Degussa P25), 
59.4 g of titanium dioxide (Bayer AG RKB2), 
12.0 g of 3,3'-5,5'-tetramethylbenzidine and 
17.3 g of a cationic polyurethane dispersion (Bayer AG KPK) 
was processed further analogously to Example 1 to give a support-based 
macroporous polymer membrane. 
b) Preparation of the impregnation solution 
0.24 g of Tetrabromophenol Blue is dissolved in 
40 ml of ethanol and 
50 ml citrate buffer (0.5 m, pH 3.3). 
This solution is made up to 100 ml with distilled water. 
After the membrane matrix had been impregnated and dried, test strips were 
produced and were tested with urine containing albumin. 
The concentrations of albumin were 0, 30, 50, 100 and 300 mg/dl. Increasing 
blue-green colour intensities could be detected, corresponding to the 
increasing concentrations of albumin. 
EXAMPLE 7 
Production of Test Strips for the Detection of Ketone 
The membrane matrix described in Example 1 was impregnated with the 
following impregnation solution: 
1.7 g of sodium nitroprusside and 
16.4 g of magnesium sulphate are dissolved in 20 ml of distilled water. 
The pH is adjusted to 9.4 with sodium hydroxide solution. 
Tests were carried out in solutions containing 0, 15, 40, 80 and 120 mg/dl 
of acetoacetic acid. A violet colouration could be observed in the 
presence of ketone, and the colour intensity increased as the content of 
acetoacetic acid increased. 
EXAMPLE 8 
Production of Test Strips for the Detection of Glucose Oxidase 
The membrane matrix containing TMB, described in Example 2, was impregnated 
with the following drink solution: 
100 KU of peroxidase and 
1.0 g of D(+) glucose in 
100 ml of citrate buffer (pH 5.5). 
After it had been dried, it was tested with the following test solutions: 
2, 10, 20, 40 and 80 U of glucose oxidase/ml in citrate buffer (pH 5.5). 
Blue-green colourations which exhibited an increasing intensity of colour 
corresponding to the increasing enzyme concentrations were observed 
immediately. 
APPENDIX 
The chemical structures of the polymers employed preferentially: 
Polyurethane (Bayer AG KBH.RTM.) 
A thermoplastic poly adduct obtained by reacting 75 parts of a polyester 
formed from adipic acid, 70 mol % of ethylene glycol and 30 mol % of 
1,4-butanediol (MW=2,000), 25 parts of a polyester formed from adipic acid 
and 1,4-butanediol (MW=2,250), 25 parts of 1,4-butanediol and 85 parts of 
diphenylmethane diisocyanate. 
##STR1## 
Cationic Polyurethane Dispersion (Bayer AG KPK.RTM.) 
The polyurethane dispersion acts as a coagulation auxiliary and is a 
cationic, emulsifier-free dispersion of a reaction product formed from 
200 parts of a polyester formed from adipic acid, phthalic acid and 
ethylene glycol (MW=1,700), 
50 parts of toluylene diisocyanate, 
20 parts of N-methyldiethanolamine and 
6 parts of p-xylylene dichloride. 
Anionic Polyurethane Dispersion (Bayer AG DLN.RTM.) 
The polyurethane dispersion is a 40% strength aqueous dispersion of a 
reaction product formed from 82 parts of a polyester formed from adipic 
acid, hexanediol and neopentyl glycol (MW=1,700), 
15 parts of hexamethylene diisocyante, 
2 parts of Na ethylenediamine-ethanolsulphonate and 
1 part of ethylenediamine.