CA1317532C - Dry reagent delivery system - Google Patents

Abstract

ABSTRACT
A method for the preparation of a dry chemistry reagent system suitable for analysis of heterogenous fluid samples, the method comprising: providing a bibulous film having an essentially uniform composition, the film being characterized as having two planar surfaces and a porosity gradient from one planar surface to the other, the inherent porosity on at least one of the planar surfaces being essentially exclusive of particular matter on the order of magnitude of cells present in biological fluid samples; sequentially imbibing into said film (i) an indicator and (ii) a reagent cocktail specific for reaction with an analyte believed to be present in the fluid sample; and contacting the bibulous film with an absorption effective amount of conditioning agent, the conditioning agent enhancing the absorption characteristics of the film to fluid samples, the contact of the film with a conditioning agent occurring either independent o f and prior in time to contact of the film with an indicator or subsequent to contact of the film with the indicator.

Description

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Title: DRY lE~EAGENT DELIYEIRY 5YSTEM

10 ~ie d of the Invention - This invention is directed to articles of manufacture and to analytical methods. More speci~lcally, this invention resides in the provisioo of a highly effective deli~rery system for dry chemistIy reagents; and, in the incorporation of this delivery system illto a plurality of diverse test strips. I~ is 15 understood that the phrase "d}y chemistry reagents" is in~lusi~e of reagen~ systems for both clinical chemist~y .assays and ~ ~
immunoassays. This~ chemistry ~reagént system is useful in the rapid and efficient analysis of lbiolo,gical fluids. One of the unique ~eatures of thi~ system is its ability to accomplish such 20 analysis of samples containing cellular and particulate ~matter~or macrc~moLecules without prior separaticln of such - endogenous:
materials ~rom the sample. Such sep~ration is generally desirable, and can be essential in certain analysis to prevent such materials from masking detection of a relpor~er molecule which is :~ ; 25 indica~ive~ of the preseflce of the analyte of in~eres~.

Description~he Prior Art - The search for a simple and effective means for performance of analytical testing of 3 0 heterogenous fluid samples, notably biological samples, has spanned more than twenty-five years. Much of ehe early work in this area was directed to the development of a reagent format which would be compatible with a simple yet effective analytical protocol. Probably one of the simpler of these sys2ems was based 35 upon the provision of a "dry reagent chemistry system"; that is, a reagent system that was imbibed into an absorbent medium, 13~ 7~

dried and reconstituted by simple addition/absorption of the fluid sample by the absorbent medium.

The patent and ~echnical literature is voluminous regarding the development and refinement of such dry chemistry reagent systems. These systems have traditionally included the reagent coated tube technology, the reagent coated bead technology and the so-called "paper" or "bibulous" layered systems. A format of dry chemistry reagent system which continues to enjoy increasing popularity is based upon single and mul~i-layered bibulous media.

One of the earlier and more successful of adaptations of the bibulous media format for dry chemistry reagent systems involved the devslopment~of a series of assays for analysis o whole blood. Some of the earlier patents in this field described the adaptation of this format to analysis of heterogenous fluids (whole blood) for glucose and other cornmon analytes (i.e. urea, cholesterol) of interest. The following ]list is representative of the patent literature directed to simple ana]lytical devices (test strips) illustrating the adaptations of dry chemistry reagent system to analysis of heterogenous biological fluids: U.S. Patents 3,061,523 (to Free~; 3,552,925 (to Fetter); 3,607,093 (to Stone); 3,092,465 (to Adams) ;3,298,789 (to Mast); and 3,630,957 (to Rey).

IJ.S. Patent ~061.523 (to Fr~:e), describes the basic chemistry 3 0 reagent system which has become the standard for colorimetric determination of glucose in biological samples. The chemistry system described by Free is contemplated for use in conjunction with a "dip stick" test. In a typical configuration of the Free invention, a solid phase (i.e. sticks or test strips) is pre-treated 3 5 with his novel chemistry formulation. The reagent treated portion of this solid phase can thereaf~er be contacted with a sample suspected of containing glucose. The intetlsity of color which is developed as a result of such contact is compared to a control or standard and a semi-quantitative determination of glucose level in the sample thereby computed.
s In the specific embodiments of the Free device, the dry chemistry reagent system is prepared by first dissolving the reactive constituents in a gelatin base and thereafter impregnating strips 10 of filter paper wi~h this dry chemistry reagent system. This is achieved by simply immersing the filter paper in the gelatin base/reagent system for a sufficient interval to effect impregnation of the reagents into the filter paper. The filter paper trea~ed ln this fashion is thereafter dried. The gelatin 15 component of the impregnating solution is reportedly essential to the uniformity of color developnnent. Presumably, the presence of the gelatin controls or inhibits ~he migration of fluids within the filter paper, thereby minimizing chromatographic separation of reagents andJor sample.
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A drop of blood (preferably whole bloocl) is then applied to the portion of the filter paper containing the dry chemistry reagent system; allowed to react with the reagents contained therein (for 25 approxima~ely 60 seconds) and, thereafter the blood ~presumably the red cells) rinsed from the paper. The intensity of the color indicator which is developed as a result of the interaction of the glucose and the reagents within the paper, is thereafter observed or measured. The recommenda~ion (if not a requirement), of the 30 Free system, that the red cells be rinsed from the surface of the test strip, implies that ~heir removal is desira~le, if not essential, to observation/measurement of the colored indicator. The rinsing of the red cells from the test strip can be expected to introduce analytical error into such analysis, thus, impairing the accuracy of 3 S the tes~ results.

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Where the technician performiDg t}liS test is dealing witb a pa~ient sample that may contain infectious microorganisms or viruses, the requirement that the sample be rinsed of red blood S cells unnecessarily exposes the technician to potential infection.

U.~. Patent 3 $52~92$ (to Fetter), reprcsents an improvement to the glucose test element described in the Free patent. Fetter 10 discloses a method and device for ef~ectively separating the whole blood sample into its serum components and into its erythrocyte componen~s (red blood cells and other color forming constituents). Fetter achieves this separation by treatment of a defined area of his sample collection device on his test elemen~
15 with certain water soluble salts. The contact of the whole blood sample with these salts in the test element results in the localized reaction of the erythrocytes (and the other colored components of the whole blood) w;th t hese salts and the resultant separation of the serum component therefrom. The serum frac~ion is~ thus, free 20 to migrate or difi~se into the test element. The migration and/or diffusion of the serum component is generally via capillary action or some other passive transport mechanism. The manner in which the sarnple is applied and the nature of the test medium, e~fectively transports and distributes the serum to ano~her 25 defined chemically reactive area of the test element containing test reagents. The test reagents of the test element are specific for one or more analytes of interest in the serum fraction (i.e.
glucose, galactose, urea, uric acid, phenylalinine and/or various enzymes).

The various configura~ions of the Fetter test element contemplate a single laminae (Figures 1 and 8), having discrete areas of chemical treatments; or a multi-layered structure, wherein a 3 5 single chemical treatment is confined to each of the layers of the laminate (Figures 3 through 7).

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Fetter also indicates that the same matrix can be used to retain both the separating reagent and the reagent specific for the S analyte of interest. In this latter embodiment of his in~ention, the whole blood sample would be applied to one side of the strip held in the horizontal position. After adequate penetration of the sample into the matrix containing both the separating and test reagents, ~he test strip would be inverted and color development 10 observed (if any) on the site opposite the site of application of the whole blood sample. Fetter is not apparently concerned with potential interference of the colored blood components with the development and/or observa~ion of the indicator species. It is, however, apparent that at low concentrations of analyte, the 15 highly colored blood components could inter~ere and/or mask the presence of the indicator from visual observation/detection.

(~anadian Patent 659.0~9 represents one of the earlier attempts 20 at preparation of a unitary d~v chemis~ry reagent system in a single layer format. The dry chemis~ry reagent system of this patent is based upon the preparation of a common slurry containing the reactive components of the system along with the ingredients of the bibulous medium (i.e. cellulose acetate). The 25 resultant slulTy is then cast and dried. The reactive components of the system are physic~lly entrapped within the resultant film/coating. The~physical nature of the film/coating lends itself to absorption of a fluid sample without release (leachlng) of the reactive components.

W,S. P,atents 3~092.465 (to Adams) describes a diagnostic device for detection of glucose in a heterogenous biological fluid sample ~i.e. blood or urine). The device consists of a bibulous medium 3 5 containing a dry chemistry reagent system specific for reac~ion with a glucose; and, the manifestation of such reaction by 3) j~, production of a visible change in color. This bibulous rnedium is provided with a "protective coating" in the form of a semi-permeable membrane. This memhrane is selective for the exclusion of larger molecules (i.e. proteins and hemoglobins) S while freely allowing the fluid fraction con~aining ~he glucose to be absorbed by the bibulous medium. This protective coating thus allows the test strip supporting the dry chemistry reagent system to be dipped or immersed in the test fluid without absorption of the colored components of the sample. The 10 protective coating of ~e sample receptive surface can then be wiped free of an interfering particulate or colored matter prior to monltoring for color change. The wiping of the surface of the analytical element can introduce analytical error into such analysis, thus, impairing the accuracy of the test results. Similar 15 error is to be expected if such debris were removed by washing or other physical n~eans.

U,~L~2~ (to Mast) desc~i~es a test article for 20 detection of glucose in heterogenous fluid samples (i.e. whole blood). I~is test article is composed oiF a layer of bibulous material impregnated with a dry chemistry reagent system. This layer is overcoated with a smooth semi-permeable film of transparent ethyl cellulose. The test device is used to detect 25 glucose in whole blood by simply applying a whole blood sample (2-3 drops) on the surface of the semi-permeable film coating which has been applied to the reagent impregnated material.
After a brief interval, the fluid fraction of the sample is absorbed by the bibulous material. The celluiar (colored) fraction of the 3 0 sample is then wiped off the surface of the semi-permeable film to allow for observation/measurement of the indica~or produced by reaction of the glucose and reagents within the bibulous layer.
The surface characteristics of this semi-permeable film are thus critical ~o the operation of this device in the analytical 3 5 environment. More specifically, the degree of smoothness of the protective film (surface porosity) is critical and must be suf~iciently fine to avoid penetration of the cellular components and hemoglobin ~ractions into the surface of the film. As noted in the discussion of the Free and Adams patents, the removal of cells and colored debris from the sample recept;ve surface of the test 5 element can introduce analytical error into such analysis.

U.S!_Patent_~607.093 (to Stone) describes a liqu;d permeable membrane, of uniform chemical composition, having within its 10 matrix, a dry chemistry reagen~t system. The membrane selected by Stone for his device is similar in its surface ~haracteristics to the protective film of Mast. The analytical protocol utilizing the Stone deYice is also similar to ~hat of Mast and requires the physical wiping of the sample receptive surface of the membrane 15 ~or removal of cellular debris and colored materials (from the sample) to allow for observation/measurement of a reaction product indicative of the presence of the analytes of interest. The Stone analytical system suffers from the same deficiency which is common to Free, Mast and Adams, previously discussed; namely, 20 the introduction of analy~ical error by required physical removal or washing of the cellular and ¢olored debris from the sample receptive surface of the analytical elemen~, prior to monitoring for indicator development.

Additional modification and enhancements have been made to the basic dry reagent chemis~ry formats described above. These modi~ications and enhancements have focused UpOIl proYidin~
multiple test zones on a common test element; increasing the 3 0 precision and colTelation of indicator development with concentrations of analyte; and, greater control in absorption/distributions of the sample within the bibulous reagent impregnated medium. The following patents are illustrative of the enhansements and modification the dry reagent 3 5 chemis~ry format: U.S. Patent 3,847,822 (to Shuey); 3,802,842 (to rJ !" ~ ~

Lange); 3,964,871 (to Hochstrasser~; and 4,160,008 (to Fenochetti).

U.S. Patent 3.8()2 842 (to Lange et al~ describes a ~est strip incorporating a dry chemistry reagent system in which a sample receptive surface of an indicator (reagent) layer is covered by a fine mesh. The indicator layer can be supported upon a "colorless" and "transparent" support. The addition of the fine mesh to this test element reportedly results in enhancement in speed and uniformity of distribution of sample upon the surface of the indicator layer. This uniformity of distribution also reportedly results in substantial improvement in reproducibility of result.

U~çnl~847.~22 (to Shuey) describes what he terms an "asymmetric" membrane c~mprising a polymer blend of polyvinyl pyrolidone and cellulose acetate. The composition of the membrane reportedly has improved ~ansport of blood solutes;
notably insulin, while being subs~antially impermeable to albumin.

U.S, ~tent 3.964.871 (to Hochs~asser) describes a disposable indica~or (test strip) having a built-in color intensity scale which is directly correlat~ed to analyte concentration with a test sample.
Accordingly, i~ is reportedly possible to simply immerse this indica~or within a test sample and observe the progressive 3 0 development in color wi~hin the various regions of the device.
The development of color (indicator) wi~hin a specific region of the test strip can thus be directly correlated with a specific concentration of analyte.

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U.$ Patent 4~iQ.QQ~ (to Fenochet~i) describes a test device for performance of a clinical analysis of a sample for dif~erent analytes on a common support. The inventor has et`fectively isolated each distinct analytical test in separate zones on the common support by elevating the reagent specific layer above the common support and providing a blotter on the support to insure against run-ofP and cross-contamination of one analytical site by another.

The next generation (at least in terms of complexity) of dry chemistry reagent systems which has evolved is a multiple layered element, having at least three discrete ~unctional layers.
These discrete functional layers are a spreading layer, a reagent layer and a signal (indicator) layer.

The performance of glucose determinations on whole blood, utilizing multiple layered films, is the subject of numerous publications and issued patents. The ~ollowing listing is representative of the technical publications in this area: Walter, B., Dry Reagent Chemistlies in Clinical Analysis, Analytical Chemistry, Vol. 55, No. 4, pp. 498-514 (April, 1983); Curme, Henry G., et al., Multilayer Film Elements for Clinical Analysis:
General Concepts, Clinical Chemis~y, Yol. 24, No. 8, pp. 1335-1342 (August, 1978); Spayd, Richard W., et al., Multilayer Film Elements for Clinical Analysis: Applications to Representative Chemical De~erminations, Clinical Chemistry, Vol. 24, No. 8, pp.
1343-1350 (August, 1978~; Ohkubo, Akiyuki, et al., Plasma 3 0 Glucose Concentrations of Whole Blood, as Determined with a Multilayer-Film Analytical Element, Clinical Chemistry, Vol. 27, No. 7, pp. 1287-1290 (July, 1981); Ohkubo, Akiyuki, et al., Multilayer-Film Analysis for Urea Nitrogen in Blood, Serum, or Plasma, Clinical Chemistry, Yol. 30, No. 7, pp. 1222-1225 (July, 1984); and, Rupchock, Patricia, et al., Dry-~eagent Strips Used for Determination of Theophyll;ne in Serum, Clinical Chemistry, Vol.

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31, No. 5~ pp. 737-740 (May, 1985). The following listing is representative of the corresponding paten~ literature in this area:
4,042,335 (to Clement); 4,ûS9,405 (to Sodickson, et al); 4,144,306 (to Figueras); 4,258,001 (to Pierce); and, 4,366,241 (to lom, et al).
s U.S. Patent 4,p42 3~5 (to Clement), describes a series of multi-layered analytical element suitable for performing chemical analysis of whole blood samples. The Clement configurations all 1 0 contemplate the application of test samples either directly, or from a spreading layer, onto a reagent layer. The reagent layer contains a complement of chemicals for reaction with a specifie analyte suspected of being present in the test sample. If the analyte is present, a "detectable species" is formed or released 15 from the reagent layer and diffuses into what is termed a "regis~ration layer" - that is, a layer whose sole function is to provide a medium or repository from which the detec~able species can be observed or measured. In order to avoid interference (masking) in the observation or measurement of the 20 detectable species, the registration layer is both devoid of the test sample and reagents used in the generation of the diffusible species. In the preferred embodiments of ~he Clement test element, an optical screen ("radiation blocking layer") is also provided between the reagent layer and the registration layer.
25 This optical screen ef~ectively optically isolates the detectable species from other constituents which could interfere in its detection andtor measurement.

3 0 As is evident from the foregoing description, Clement attempts to segregate the individual functions of his analytical element into discrete layers. This technique, although potentially attractive to a manufacturer in possession of technology for fabrication of multi-layered elements, is by its very nature unduly complex and 35 potentially troublesorne due to the mechanical instability of these composites. More specifically, where this test element is to be 13 ~ ~ r ~
1. 1 used by an individual in a self-tes~ environment, the composite must necessarily be supported on an additional element to lend physical integrity to the multi-layered element and thereby prevent its unintended flexing and potential separation of the 5 various layers eontained therein.

U.S. Patent 4~p5~.405 ~to Sodickson, et al), describes a method and apparatus for glucose analysis of whole blood samplss. In the 10 Sodickson system (as described in Exarnple 1 d.), a reaction site is initially prepared by pre~orming wells in a polyox resin treated filter paper. A reaction site is physically defined in this treated paper by impressing thereon a confining ring approximately one cen~imeter in diameter. A glucose reagent is then applied to the lS reaction si~e defined by this ring and the reaction site dried. An ultrafiltration membrane is placed over the well and a sheet of paper containirlg a dried blood spot plac~d in contiguous relationship with the ultrafiltration msmbrane. The dried blood spot is then reconstituted by the addition of s~line. 'rhe 20 apparatus used in the Sodickson system (i.e. press) confirles the reconstituted blood sample in the reaction well for a brief incubation period. During thls incubation period, soluble components of the whole blood sample are redissolved in the saline and pass through the ultrafiltration membrane where they 25 come in contact with the glucose test reagents in the polyox treated paper. The cellular componeDts of the blood are retained on the ultrafiltration membrane and thereby prevented from interference with the development and/or measurement of the glucose manifesting indicator~

The system described by Sodickson, as contemplated in his P.xample 1 d., is cumbersome (requiring reconstitution of the blood sample and relatively cvmplex equipment to effect 3 5 separa~ion of cellular componen~s from the whole blood sample~
and does not readily lend itself to self-testing.

ll.S._Pat~t 4,1~,~Q~ (to Figueras), describes a multi-layered analytical element analogous to that of the Clement patent 5 (previously discussed). The E~igueras chemistry differs from Clement in that the interaction of an analyte and nvn-diffusible reagents in the reagent layer, results in the release of a "preformed detectable species" which can migrate from the reagent layer into a registration layer. This preformed detectable 10 species is then observed or measured in the registration layer.
Figueras contemplates (as described in his Example VI) the adaptation of his system to glucose analysis of whole blood. The separation of colored and cellular components of the whole blood would be achieved by Figueras in essentially the same fashion as 15 in the Clement patent. The introduction of the whole blood sample into the reagent layer of the Figueras element results in the release of a di~fusible preformed photographic dye, which is then free to migrate into the registration layer. Figueras requires the presence of the same type of optical screen (radiation 20 blocking layer) between the reagent layer and the registration layer to avoid m?sking or interference in detec~ion of the~dye from the non-diffusible color components (i.e. sample and reagen~s) in the reagent layer. The limitations and disadvantages noted in the discussion of the Clement patent are also applicable 25 to the multi-layered analytical element of Figueras. Figueras, however, introduces an additional complexity; namely~ the e~fective immobilization of ~he reagents within the reagen~ layer and the preservation of the preformed indicator prior to its release by the analyte of interest. Because of the requirements of 3 0 maintenance of fluid coiltact between the various elements of the Figueras composite, its snechanical properties are critical.
Accordingly, the multi-layered element of Figueras, as previously noted for Clement, will require a supporting (transparent) layer to lerld physical integrity to this device.

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11.$. Patent 4,25~,001 (to Pierce et al), describes a multi-layered analytical element (of the type descr;bed in both Clement and Figueras - previously discussed) incorporating a unique spreading layer. The spreading layer of the Pierce patent is described as an S essentially "non-fibrous" material. In one of the preferred embodiments described by Pierce (Figure III), the spr~ading layer can contain "interactive compositions" (test reagents) for reaction with analytes in a test sample. Pierce also contemplates the use of her device in the analysis of whole blood, blood serum 10 and urine. Whole blood can be applied directly to the Pierce element. The presence of red blood cells will not repor~edly interfere with spectrophotome~ric analysis if carried out by reflectance measurements, provided a radiation screen (blocking layer) is used to screen out interference from the red cells (column 26, line 49-61).

As is evident from the above patent, the Pierce device is designed to "take up" the whole blood sample. Thus, both cellular and non-2 0 cellular components of the whole blood are imbibed by thespreading layer. The spreading layer of Pierce is, therefore, not intended nor contemplated as a means for separation of the cellular fraction of the blood from the serum fraction. Where enzyme based diagnostic clinical assays are incorporated into the 25 spreading layer (as in the case of glucose analysis3, the potential for inhibition of these enzymes by the erythrocytes can potentially mask low concentrations of glucose and, thus, distort an otherwise clinically significant result.

The transport and spreading of biological samples is of con~ern, not only in dry chemistry reagent systems for performance of clinical assay, but also in the dry reagent systems utilîzed for immunoassay of the same biological fluids. The following U.S.

3 5 Patents are represen~ative of the immunoassay literature in this ~ 3 :~ 7 1~ ~3 ~

area: U.S. Patents 4,094,647 (to Deutsch); and, 4,366,214 (to Tom et al~.

S I~.S Patent ~ 4~647 (to Deutsch), describes a linear wick having defined areas for placement of reagents and sample. The end of the wick is placed in a vertical position in a developer fluid and the fluid drawn up the wick by capillary action. As the fluid is drawn into the wick, it transports ~he reagents and sample, from 10 their respective locations, into contact with one another~ One or more of these reagents can be immobilized on the wick; thus, the developer fluid is used to transport reagent and sample to the immobilized reagent and any unreacted or mobile materials from the immobillzed reagen~. The site having the immobilized 15 reagent can then be viewed or measured for the presence of analyte.

U.~_Patent 4~36~241 (to Tom et al~ describes a device for the 2 0 non-chromatographic immunoassay of biological fluids. In the Tom device con~iguration, a test element, having a relatively small test zone, is ~treated with an immobilized birlding material (termed "mip" or 'imember of an immunological binding pair").
The test zone of ~his device is the exclusive entry po~ ~or the 25 biological sample and is designed for receipt of the biological sample either by direct application or immersion in the test fluid.
The analyte (if any) contained in the biological sample is selectively ~immunochemically) bound in the test zone to the immobilized binding material which is specific for this analyte.
3 0 The residual components of the sample, including the fluid component thereof, are drawn from the tes~ zone to a second element which is in fluid contact (contiguous relationship) with ~he test zone. The second element's function is to pump or draw the biological sample through the test zone into the test element.
3 5 Those constituents of the sample which are not bound in the test zone are, thus, drawn into the test element and away ~rom the test zone.

5 In the immunological test element of the type described by Tom, the pretreatment of the test zone effectively confines the analyte and the test reagents (i.e. labelled indicator) to the analysis site, thereby essentially eliminating the problems of reagent and sample migration (which are common in the solid phase systems 10 designed for clinical chemis~ry analysis). These immunoassay systems of Tom are not, howeYer, without their disadvantages, the most common being the nonspecific binding of inter~ering substances in the reaction zone and the difficulties which are sometimes inherent in the detection of low levels of analyte.

U,S. Paten~ 4~46.232 (to Liotta) describes a multiple layer test device for immunoassay. This device and test protocol are directly arlalogous to the Figueras patent (previously discussed).
20 The addition of sample containing an analyte of interest results ~in the displacement of a previously immobile species. In tlhe system described by Liotta, the compvnent of the reagent system which is displaced is an enzyme conjugated to a member of an immunological binding pair Shereinafter "conjugate"). The 25 conjugate is then calried into the larninate where it can effect production of a detectable species.

As is evident from the foregoing discussion of the references 3 0 appropriate for whole blood analysis, each type of test element generally requires a plurality of lamina in i~s pre~erred con~iguration. Where a single layer (component) test device is suggested, none of the references, with one exception (U.S.
3S607,093-to Stone), either acknowledge or appreciate the 3 5 poten~ial chemical and op~ical interference of the erythrocyte population (and other colored components of the blood), on the lS ~ ~ ~ 7~j ~) analytical protocol or in the de~ection of the reaction product which is indicative of the presence of the analyte (namely, the glucose~. Where immobilization techniques (as described in Fetter, I)eutsch and Tom~ are employed, the specificity of the 5 binding reaction can, under certain conditions, be indiscrimina~e.
In the case of Fetter, the attempt at scavenging of erythrocytes and other colored components from the sample with certain salts (that have been imbibed within the test medium), is not without its limitations. In the single layered element of Fetlter, the serum 10 fraction is radially separated from the colored component of tlle blood and thereby results in the distribution of the analyte over a relatively large area. If the analyte is present in low concentrations, it can easily escape detection. Thus, some amplification mechanism may be required ~or visualization of a 15 low level of analyte ~i.e., the use of an enzyme in conjunction with a chromogenic substrate).

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The immunochemical device and techniques of the type described 20 by Deutsch, Tom and Liotta are not readily compatible with whole blood analysis. It is possible to wash the test element for removal of the cellular debris (as is suggested in the Free patent), however, the effect of such additional step upon the immunochemical binding process is not known and can be ~S expected to introduce analytical error in such analysis. Such manipulations of the test element can also be expected to mask detection of the analyte manifesting reaction or removal (in part) of the indicator species which is indicative of the analyte of interest. In addition, such physical removal of cellular and 3 0 colored debris will necessarily expose the clinician or the person performing the test to potential infection by those components of the blood which are removed from the test element.

3 5 In summary, it should now be apparent that ~he prior art lacks a simple yet accurate device for analysis of whole blood. Where 17 ~3~7~z~l such devices have been proposed, they are complex, do not readily lend themselves to self-testing without the provision of a fixture or additional support mechanism, and generally lack the sensit.ivity to permit differentiation o~
different levels of analyte over a broad clinical range of concentration. Moreover, all such devices discussed above (with the exception of the Stoene patent) would appear to have one common failing; namely, their inability to effect optical (and in certain instances, chemical) isolation of erythrocyte and other colored components of the whole blood ~rom the observation/measurement site without the physical removal of the erythrocytes from the test element; or, the provision of some optical screen (blocking layer) between the colored components of the sample and the indicator compound which is generated as a result of the clinical assay.

This invention remedies the above and related deficiencies in the prior art~
More specifically, this invention provides a dry reagent delivery system for clinical and immunoassay of biological fluids.

25 This invention can also provide a dry reagent delivery system which is effective in the analysis of biological : fluids containing cells, particulate matter and macromolecules (hereinafter collectively referred to as "interferents") without pretreatment (i.e. filtering or centrifugation) or dilution of the biological fluid or the chemical removal/neutralization of such interferents.

This invention can also provide a dry reagent delivery system suitable in the rapid and efficient analysis of whole blood for one or more analytes of interest, without prior separation of the serum from the cellular fraction.

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In accordance with another aspect this invention provides a dry reagent delivery system suitable in the rapid and efficient analysis of urine for one or more analytes of interest, without prior concentration and/or chemical extraction of the analytes of interest from the urine sample .

It can also provide a dry reagent delivery system suitable in the rapid and efficient analysis of saliva for one or more analytes of interest, and can be both self-contained and does not require any additional instrumentation or extensive training for performance of a diagnostic assay or interpretation of the result.

The dry reagent delivery system of the invention is stable and retains its potency and activity until placed in use by contact with a biological fluid.

SUMMARY OF THE INVENTION
Thus, there is provided a dry reagent delivery system comprisin~ a conditioned membrance containing a complement of reagents which are specific for reactions with one or more analytes of interest. The interaction of the analyte(s) and such reagents is manifest by the release or formation of an indicator molecule which is indicative of the presence or absence of the analyte in the sample. The sample receptive surface of the membrance is relatively dense, thereby being exclusive of cells, particles and/or macromolecules which can potentially interfere with reaction of the analyte and the reagent system and/or mask the detection of a reporter molecule.

The opposing surface of the membrane, by way of contrast, is substantially less dense (more porous), thereby allowing for infusion of the xeagent system during manufacture; and, '~' 1 3 ~ 7 ~ 3 ~
the formation, diffusion and visualization of a reporter molecule, which is indicative of the analyte of interest.

The dry reagent delivery system can be configured as a component of test strips for analysis of whole blood samples, urine or saliva. In each of these configurations, it is contemplated that khis sample receptive surface of the membrane shall be the exclusive means of access of the biological fluid to dry reagent system.
In accordance with one aspect of this invention, there is thus provided a method for the preparation of a dry chemistry reagent system for analysis of heterogenous fluid samples, said method comprising:
(a) pr~viding a porous membrane having an essentially unifor~ composition, said porous membrane being characterized as having two planar surfaces and a porosity gradient from one planar surface to the other, the inherent porosity on at least one of said planar surfaces being essentially exclusive of particulate matter on the order of magnitude of cells present in biological fluid samples;
(b) sequentially imbibing into said porous membrane (i) an indicator and (ii) a reagent cocktail specific for reaction with an analyte believed to be present in the fluid sample; and (c) contacting said porous membrane with an absorption effective amount of conditioning agent, said conditioning agent enhancing the absorption charactaristics of the porous membrane to fluid sam-ples, said contact of said porous membrane with a conditioning agent occurring either independent of and prior to time to contact of said porous membrane with an indicator or subse~uent to contact of said porous membrane with said indicator.

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Also provided is a dry chemistry reagent system ~or detection of an analyte in a heterogenous fluid sample, said system comprising:
a porous membrane of essentially uniform composition and a porosity gradient from one planar surface thereof to the other, whe~ein said porous membrane's inherent fluid absorption and distribution characteristics have been modified by imbibiny a conditioning agent, an indicator, flow control agent and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform di~tribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said : 15 film so as to enhance the uniformity of absorption and modulate the rate of absorption of the fluid sample ; and its interaction with the reagent cocktail.

: In addition, there is provided a analytical method for screening a heterogenous fluid sample for an analyte of interest, comprising:
(a) providing a dry chemistry reagent system com-prising a porous membrane of essentially uniform composition and a porosity gradient from one planar 2~ surface thereof to the other, wherein said porous membrane's inherent fluid a:bsorption characteristics have been modified by sequentially imbibing a conditioning agent, an indicator, flow control agent and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform distribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said porous membrane so as to modulate both the rate and the uniformity of.-absorption of the fluid sample and its interaction with the reagent cocktail;

19b ~b) applying a heterogenous fluid sample to the sample receptive surface of the bibulous medium o~ the reagent system; and (c) monitoring the surface of the bibulous medium opposite to the sample receptive surface for a change of color or fluorescence or for the development of color or fluorescence.

Also there is provided a test kit for analysis o~ a heterogenous fluid sample, said kit comprising:
(a) dry chemistry reagent system comprising a porous membrane of essentially uniform composition and a porosity gradient from one planar surface thereof to the other, wherein said porous membrane inherent fluid absorption and distribution characteristics ha~e been modified by sequentially imbibing a conditioning agent/ an indicator and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform distribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said film so as to modulate both the rate and uniformity of absorption of the fluid sample and its interaction with the reagent cocktail; and (b) a standard for comparison with the indicator of the dry chemistry reagent system.
B

:L 3 ~

5 In each of the following figures, the perspec~ive view is oriented to the side of the ~est strip intended for application of the biological sample.

10 Pig. 1 is a perspecdve view in partial cross-section through the reagent delivery system of this invention.

Fig. 2 is a perspective v;ew of a test strip for analysis of a whole 15 blood sample incorporating the reagent delivery system of Fig. 1.

Fig. 3 is a cross-sectional view of the test strip of Fig. 2 at section 3--3 .
20 ~ ~ ~

Fig. 4 is a perspect;ve view of a test strip ~r analysis of a urino sample incorporating the reagent delivery system of Fig. 1.

~ig. S is an altemative embodiment of the test strip of Fig. 1.

Fig. 6 is ~n alternative embodiment of the test strip of Fig. 1.

Fig. 7 is a cross-section of a test strip in which a component of the dry chemistry reagent system is coated on the sample receptive surface and the balance of such system within its matrix.

3; ~

E'igs. ~ (a) and (b) are cross-sections of test strips havlng conti~uous wicking or spreading layers.

5 Fig. 9 is a device t~r monitoring the reaction of analyte with a dry chemistry reagent system of the test strip of Fig. 8(b).

DESCRIPl[`ION OF l'HE INVENTION
~

The reagent delivery system of this invention is unique in (a) the proYision of a conditioned membrane within which the analysis of ~he fluid sample is conducted; (b) the manner of-dis~ibution of the analyte speci~lc reagents within ~the membtane; and,~ (c) in the ability to e~fectively segr&gate the various fractiorls of a he~erogenous sample.: ~his segregation is essential to effeceively isolate the compo~lent of the sample which is to be subjected ~o analysis from the fraction of the samp]le which can potentially ter~ere with th~ reaction of ~he analyte and~ the reagents specific ~or its;detection, or otherwise mask the detection of a reporter molecule, which is indicative of th~ presence or absence :: of the ana1yte of interest. ~e ability to physically~ exclude a :: 25 portion of sample fronn absorption by the membrane is based~
upon a combirlation of factors, including the inherent density of the sample recepeive surface of the membrane and the distribution of the constituents of the reagent delivery system within the matrix of the conditioned membrane.

1`he membrane which is suitable as a repository of the dry chemistry reagent system is, prior to conditioning, anisotropic, in that there exises a density gradient from one planar surface to the 3 5 other. The density gradient is typically produced as an incident to its manufacturer. More specifically, where the constituents of ~ ~ ~ rJ ~

the membrane have been cast from a slurry, the part;cles of the slurry tend to settle (prior to and during the evaporation of the casting fluid) upon a supportive surface. S:)nce the casting fluid has evaporated, the membrane ~rms a self-supporting film and 5 can be separated from this supporting surface. The settling of particles of the slurry tends to create a more compact (dense) membrane surface contiguous ~o this supporting surface. The constituents from which the membrane can be prep~red include both synthetic and naturally occurring materials, i.e., nylon, 10 cellulose acetate, cellulose acetate - nitrate esters and mix~ures thereof.

The membrane's physical characteris~ics (tensile strength, 15 thickness, etc.) are of course to be consistent with test strip manufacture; that is, it should have sufficient dimensional stability arld integrity to permit sequential absorption and drying of the conditioning agent, the reagent cocl~tail and/or indicator without loss of its physical strength. The physical attributes of 2 0 the membrane should also preferably ]provide sufficient durability and flexibility to adapt to automated processes for continuous manufacturing of test strips. The physical charac~eristics of the membrane should, in addition, be otherwise consistent with the absorption and retention vf aqueous fluids in 2 5 the contemplated environment of use.

The membrane must also be relatisrely chemically inert; that is, essentially unreactive toward both the constituents of the 3 0 chemistry reagent system and toward the constituents of a sample which is to be reacted with the reagent system within the membrane. It is, however, to be anticipated that certain of the inherent qualities of the membrane surface and/or its matrix may exhibit some affinity for a constituent of the reagent system 3 5 and/or a constituent of the fluid sample. This natural attraction can, in cer~ain instances, be- used to advantage to immobilize a ~ ~ ~ r) ~

constituen~ of the reagent cocktail and/or sample on or within a portion of the membrane and thereby effect a type of separation or anisotropic distribution of the constituents of the cocktail/sample. l`his ~ype of separation, based upon natural 5 binding affinity of the membrane, can be used to advantage in both clinical chemistry assays and in immunoassay.

The membrane's optical properties should also enable effective 10 observation/monitoring of the reac~ion manifesting indicator species. This requirement would, thus, contemplate that ~he membrane provide a background of suf~icient contrast ~o permit observation of the indicator species at relatively low concentrations. Where the indicator is a fluorophore, the 15 background fluorescence of the rnembrane should be minimal or be essentially non-fluorescent at the monitored wavelength of interest.
.

20 Where the inherent characteristics of the membrane are not conducive to effective monitoring of an indicator, it may be desirable to in*oduce a pigment into the dry chemistry reagent system. For example, cer~ain of the membranes which may be potentially suitable for use in this invention can be colored or 25 transparent. The introduction of pigment into the chemistry reagent system provides a suitable background against which to measure the indicator species.

3 0 The transparency of the membrane can, however, be used to advantage in both nephelometry and photo-fluorometric assays in which the presence or absence of analyte in the sample is manifest as a change in turbidity in the fluid phase. The dry chemistry reagent for such turbidimetric reaction systems will 3 5 typically include a color, transparency or background modifying ~4 ~ 3~P~
pigment which is absorbed into the membrane; preferably along with the conditioning reagent.

In order to better illustrate the unique features noted above, the reagent delivery system will now be described by reference to a test strip which contains reagents specific for the detection of 10 glucose in whole blood.

The standard chemistry reagent system for detection of glucose has been previously described in U.S. Patent 3,061,523. The basic l5 complement o~ interactive materials which are required in the reagent to produce a coloIimetric reaction for detection of glucose are glucose oxidase, peroxidase, o-tolidine dihydrochlorîde, and buffering salts/acids.

~or the purpose of this illustration, the fluid absorbent medium utilized in this reagent system can be anyone of a variety of synthetic (preferably cast) mernbranes having a relatively dense surface (pore size <0.5 microns) and a relative less dense surface 25 (pore size >1.0 microns).

The oFder of absorption of the constituents of the dry chemistry reagent system into the membrane is generally dictated by considerations involving chemical compatibility and/or other 30 factors relating to solubility in a common solvent. Since the o-tolidine solution is highly acidic it is incompatible with the enzymes of the reag~nt systern and, thus, each are absorbed into the membrane separately.

s~3 ~

Initially, the membrane is conditioned by treatment with a first solution containing protein, glucose, dextrin or dextrans, starch, polyethylene glycol (PEG), polyvinyl pyrolidone (PVP), or an e~quivalent. The purpose of such conditioning is two-fold: (a) to 5 effectively reduce the void space within the matrix of the membrane and, (b) to assist or promote the absorption of the fluid fraction of the biological sample. In an alternative embodiment of the method for preparation of this reagent system, the conditioning agent can be combined with one or more 10 of the interactive materials of the reagent system and concurrently absorbed into the membrane. Where the conditioning agent is combined with the interactive materials of the reagent composition, ilts absorption by the membrane will necessarily be preceded by absorption of the indicator molecule.

Where such conditioning of the membrane is effected independent of the interactive materials of the reagent systern, the membrane is dried under con~ollecl conditions, and then 20 contacted with a second solution containing the indicator molecule (or the chemical precursor of the indicator molecule)~ The absorption of the indicator molecule (or its precursor) Gan be effected ~rom either the less dense or nnore dense surface of the membrane, with preference being given to ~he less dense surface.

Following the absorption of the above solution, the membrane is once a~ain dried under controlled conditions ~o preserve the uniformity of distribution of the non-fugitive constituents of this 3 0 solution.

The membrane is then contacted with a third solution containing the balance (interactive materials) of the reagent system. The 3 5 absorption of this solution is preferably effected by simply contac~ing the less dense surface of the membrane and this ~æ~ ~7 r~

solution and allowing the membrane to soak up the solution like a blotter. This third solution also contains what can be functionally described as a "flow control agent". This agent modulates the rate of spreading/distribution of the fluid fraction of this sample S throughout thc matrix of the membrane. It is, thus, effective in the prevention of the chromatographic separation of the reagents within the membrane matrix upon the addi~ion of the fluid sample. Following addition of this third solution, the membrane is air dried for removal of excess fluid, lyophilized and shielded 10 from light. The foregoing practices are necessary and appropriate for maintenance of uniformity of reagent distribution and protection against photo-degradation of the indicator.

l S Once the reagent delivery system has been prepared as described above, the resultant membrane can be adapted to any one of several test s~ip configura~ions specific for the analysis of whole blood, urine or saliva.

Fig. 1 is illustrative of the internal structure of the reagent delivery system of this invention. The sample receptive surface (2) of the membrane (3) is essentially impermeable to cells and particulate matter. By way of contrast, the opposing surface ~4) 25 is relatively porous. The matrix (6) of the membrane is fairly non-descript, except to note that i~s illherent void space has been reduced substantially from that originally provided by absorption of the conditioning agent, indicator, interactive reagents and flow control agents. Thus, the relative density of the original 3 0 membrane has been effectiYely increased. The density of the membrane containing the dry reagent system is believed to be critical to performance of assay and the uniformity of the membrane. As noted previously, the controlled drying and shielding of the indicator from photo-degradation are critical to 3 S both effective and consistent performance. The membrane uniformity is also critical to consistent performance of the ~est ~l 3~

strip. The cast membranes have proven to be of more consistent quality and uniformity and are, thus, preferred for the test strip of this invention.

Fig. 2 provides an ;llustration of the membrane (3) in a test strip (20) intended for analysis of a biological fluid. This test strip configuration is intended for use in a protocol contemplating the application of the biological sample to the sample receptive 10 surface (2) of the membrane, allowing for adsorption of ~he fluid fraction of the sample into the matrix (6) of the ms:rnbrane and detection of an indicator molecule by inversion of the test, and visually observing indicator development from the more porous surface (4) of the membrane. This test strip can also be inserted 15 into a reflectance meter, nephlorometry (measures turbidity), a photometer or ~luorometer of the type illustrated in Pig. 9; and, the repor~er molecule measured~ and compared with a standard curve for the analytc of interest. The instrument will then report a value based upon its observation and comparison with a 20 s~andard.

In one of the preferred embodiments of this invention, the dry chemistry reagent system of Figs. 1 and 2 is used ;n conjunction 25 with means for preconditioning/treatmenl/modification (hereinafter collectively referred to as "enhancement") of the whole blood sample to improve deteetion of the analyte of interest. Such enhancement can be performed separated and apart from the test s~rip, or preferably by the addition or 3 0 integration of sample enhancement means into the tes~ strip configuration. More specifically, in the adap~ation of ~he dry chemistry reagent system of this invention ~o a cholesterol assay, it has been found advaDtageous tO first adsorb ~he whole blood sample into a porous compressible, sponge like material (i.e.
3~ fiberglass, neoprene or Gellulose pad). This pad can be treated with a saline solution containing any one or combination of agents ;

28 ~3~
which enhance the ability of the dry chemistry reagent system to accurately dletect the presence and/or qwantify the analyte of interest. Once the sample has been enhanced by contact/interaction/adsorption by the pad, the sample is S expressed ~rom the pad onto the sample receptive surface of the test strip, and the reaction thereof with the dry chemistry reagent system proceeds as previously described.

10 In another alternative embodiment of this invention, the dry chemistry reagent system of Figs. 1 and 2 is used in conjunction with means for enhancement of the whole blood sample to improve detec~ion of high density lipoproteins ~HI)L). Since the bod~y's ability to absorb and/or transport cholesterol, is 15 dependent upon the density (molecular weight) of the lipopro~eins (which are polymeric compounds associated with the steroid), the importance of measuring and quantifying HDL, from the total cholesterol, and/o~ from low density lipoproteins (hereinafter "LDL",~ can be of paramount importance. In, for 20 Example 5, the sample condi~ioning pad is pretrea~ed with the reagents which precipitate the low density~ lipoproteins. After waiting for a brief period for this interaction of preconditioning ~o be completed, the conditioned sample is expressed onto the sample recep~ive surface of a cholesterol test strip which has 25 been optimized fc>r hi~her sensitivity to cholesterol. Since the precipitated LDL are trapped along with a portion of the cellular fraction of the sample within the preconditioning pad or on the relatively dense surface of the membrane of the test strip, only the HDL (predominantly) reaches the dry chemistry reagent 3 0 system within the test strip, thereby initiating a color reaction which is manifest on the opposing surface of the test strip. The indicator produced as a result of this reaction can be observed or measured quantitatively and, thus, correlated with the amount of HDL present in the sample.

2 9 ~ t~ ;3 Fig. 3 provides a cross-sec~ional v;ew ~hrough test strip of Fig. 2 at line 3,3. The membrane ~3) is sealed within the components of the test strip by an envelope (22,24) to insure confinement of the test sample upon the sample receptive surface (2) of t~e S membrane. This sealing of the membrane within the envelope simply involves the placement of a piece of water insoluble adhesive (not shown) along the planar surfaces of the envelope which are in contact with the planar surfaces of the membrane.
In the configurations illustrated in Fig. 2 and Fig. 4, the sample 10 receptive surface (2) of the membrane (3) is exposed from above and below through a pair of apertures (24926) in the envelope.
The aperture (26) that exposes the sample receptive surface (2) of the membrane de~lnes the lateral dimensions of a well (70) in which the sample is confined. This confinement of the sample 15 (99) is more fully iDustrated in Fig. 6.

The second aperture (24) in the envelope exposes the underside (4), or the more porous surface, of the membrane, thereby 20 permit~ing monitoring of a reac~ion prolduct which is indicative of the presence or absence of an analog of interest. This ability to observe/measure such reaction product (hereinafter "indicated") without physical removal of the sample residue from the sample receptor surface of the membrane, or optically masking such 25 residue with a separate "blocking layer" (optical screen) is unique to the dry chemis~y reagent system of this invention.

The test strips illuslrated in Figs. 4 and 5 incorporate the same 30 basic elements of the test strip of Fig. 2 with certain enhancements. More specifically, the test strip of Fig. 4 incorporates a protective film (60) which effectively precludes sample from contact with the underside of the membrane. This tes~ s~ip is, thus, suitable for immersion in a fluid sample (i.e.
3 5 dipstick) to effect contact of the sample with the sample receptor surface of the membrane. A slot (62), or air bleed, is provided in ~3~

the surface of the envelope ~o allow for the escape of air trapped in the cavity (not shown) which is formed between the protective film (60) and the underside of the membrane (43.

The test strip illustrated in Fig. 5 incorporates a flap (80) which can be separate from or integral with the test strip. This flap is provided with a pressure sensitive adhesive (not shown? which emables the user to effectively seal the sample (99) within the 10 well (70) defined by the aperture of the envelope and the sample receptor surface of the membrane. This confinement of the sample within the test strip provides significant protection of the clinician from inadvertent contact with an infectious specimen;
and, also prevents unintended transfer of sample residue to 15 surfaces of an analytical device (i.e. fluorometer) which can be used to monitor the concentration of an indicator produced within the membrane. With respect to this latter point, the test strip is compatible for use in a va~iety of environments, including use with a monitor of the type illustrated in Fig. 9.

In practice, a test strip (100) of the configuration of Fig. S (having a sample sealed witlhin the specimen well) is inserted into the read station (not shown3 of the monitor (104). This is 25 accomplished by simply raising the door (106) located on the tvp of the monitor housing and positioning the test stnp within the read station of the monitor. ~he test strip is oriented in a manner to align the aper~ure on the underside of the test strip with the photo optical elements (not shown) of the monitor. The 3 0 placement and orien~ation of the test strip generally in~olves at least some contact of one or more surfaces of the chamber housing and photo optical elements with the test strip. The failure to isolate the sample in the manner illustrated in Fig. S
~ill inevitably result in contamination of this chamber and 3 5 possible damage to the monitor, or introduction of imprecision in the measurement of subsequent sarnples. After the requisite 7 ~ J

interval, the monitor has had an opportllnity to measure the level of indicator in the test s~rip~ The test strip is then removed from the monitor and discarded.

Fig. 6 is illustrative of an alternative embodirnent of an envelope for a test strip of this invention. This envelope has multiple apertures and is designed for containment of separate pieces of membrane containing different dry chemistry reagent systems.
10 Accordingly, a device of this configuration has the potential for performance of a clinical chemistry profile analysis of an individual patient sample on a single test strip.

15 Fig. 7 is illus~rative of an embodiment of the dry chemigtry reagent system of this invention in which a component of the reagent system is deposited upon the sample receptive surface of the membrane as a thin ~ilm or coating (103). The separation of the constituemts of the leagent system form one another in the 20 dry stage is only a temporary condition. Upon applicatioll of the fluid sample to this coating, it is antici~pa~ed ~hat the analy$e of interest will displace a component of the reagent system or somehow reaet therewith~ thus, permittimg this component of the reagent system to be freely absorbed into the membrane where it 25 can initiate a discernible reaction which is indicative of the presence or absence of the analyte OI interest.

Fig. 8(a) is illus~ative of a dry chemis~ry reagent sys~enn having a 3 0 spreading layer (120) in a contiguous relationship (i.e. fluid contact) with the sample receptive surface (2) of a membrane (3).
The spreading layer facilitates the distribu~ion of sample on the sample receptive surface of the membrane and may also be used to effect a lateral transport of ~he sample from one portion of the 3 5 membrane to another.

7. ~ ~dllio~al Dr~ ~j~L~

The above discussion, with respect to glucose analysis of whole blood, can by analog be readily e~trapolated to the preparation of test strips and performance of clinical assays for a variety of other analytes typically found in biological fluicl samples. The conditioned membrane system of this invention is, thus, applicable to clinical analysis of cholesterol, triglycerides, 10 bilirubin, creatinine, urea and alpha-amylase. The assay format can be essentially the same as that described previously for glucose, or optionally involve the combination of the conditioned membrane/reagent system with one or more additional lamina (i.e. spreading layer, radiation blocking layer, semipermeable 15 diffusion layer, etc.).

, :
The preparation of a conditioned membrane, incolporating- a dry chemistry reagent system for each of the above analytes? follows 2 0 essentially the same process as described for preparatioll of glucose specific dry chemistry reagent sys~ems (e.g. conditioning the membrane wi~h a flow control agent and the absorption of the indicator/reagent cocktail). The conditioning of the membrane can, thus, occur prior to or concurrent with contact OI the 25 membrane with one or more of the constituents of the dry chemistry reagent systems.

A test strip for urea can be prepared by absorption, into a 3 0 conditioned membrane, of appropriate concentrations of urease, buffer, and an indicator sensitive ~o changes in pH. When a whole blood sample is brought in contact with the sample receptive surface of the membrane, the serum is taken up by the membrane. The urea present in the serum is digested by the 3 5 urease enzyme, thereby liberating ammonia in solution. The ammonia Gan then react with a suitable indicator (i.e., a ~ 3~

protonated merocyanine dye). The pH of the membrane is buffered to about 8.0 to keep the equilibrium concentration of the ammonia relatively low. The indicator is monitored at 520 nm.
Additional de~ails of this specific reagent system are described in 5 the open literature, see for example Spayd~ R.W. et al., Clin. Chem., Vol. 24, No. 8 (1978) 1343.

A test strip for alpha-amylase can be prepared by absorption, 10 into a conditioned membrane, of appropriate concentrations of a derivatized substrate (i.e., starch) and buffer. When the whole blood sample is applied to the sample receptive sur~ace of the test strip, the serum is absorbed into the membrane~ thus, initiating digestion of the derivatized substrate by the alpha-15 amylase in the sample. This digestion of the substrate releases achromophore or fluorophore which can be monitored in accordance with accepted techniques and readily available equipment. ~ Additional details for this specific reagent system also appear in the Spayd publication, previously referenced 20 herein.

A test strip for bilirubin can be prepared by absorption, into a conditioned membrane, of appropriate concentrations of certain 25 cationic polymers ~i.e., polymeric quaternary salts) and phosphate buffer (pH approximately 7.4). When a whole blood sample is applied to the sample receptive sur~ace of ~he test strip, the serum is absorbed in~o the membrane, thereby initiating interaction of ehe bilirubin and the cationic polymer. Such 3 0 interaction results in a shift in the maximum absorption of the bilirubin ~rom 440 eo 460 nm with an accompanying substantial increase in absorption at the new peak. Additional details relating ~o this specific reagent system also appear in the previously referenced Spayd publication.

34 ~3~_7f;'~,',~,,~', A test strip for triglycerides (triacylglycerols) can be prepared by absorption, into a conditioned membrane, of surfactant, lipase, adenosine triphosphate (ATP~, glycerol kinase and L-alpha-glycerol phosphate oxidase, and a triarylimidazole leuco dye. In S brief, the surfactant aids in dissociation of the lipoprotein complex so that the lipase can react with the triglycerides to form glycerol and fat~y acids. The glycerol is then phosphorylated with the adenosine triphosphate in the presence of the glycerol kinase erlzyme. The L-alpha-glycerol phosphate thus produced is then 10 oxidized by the L-alpha-glycerol phosphate oxidase to dihydroxy acetone phosphate and hydrogen peroxide. The hydrogen peroxide oxidizes the leuco dye, producillg a colored indicator which has a peak absorption a~ 640 nm. Additional details relating to this specific reagent systern appear in the previously 15 referenced Spayd publication.

An alternative and preferred chemistry reagent system for triglyceride analysis can be prepared by absorption, into a 20 conditioned membrane, of lipase, glycerol dehydrogenase, p-iodonitrotetrozolium violet (INT) and diaphorase. The serum triglycerides initially interact with ~he chemistry reagent sys~em and are hydrolyzed to free glycerol and fatty acids. The free glycerol is now converted to the dihydroxyacetone by glycerol 25 dihydrogenase, in the presence of NAD. Simultaneous with such conversion, INT ~colorless) is reduced by diaphorase, in the presence of NAI)H, to red dye (maximum, gamma = 500nm). The change in absorbance of the test strip a~ SOOnm is directly proportional to the concentration of serum triglycerides.

A test strip for determination of total cholesterol in serum can be prepared by absorption, into a conditioned membrane, of cholesterol ester hydrolase, cholesterol oxidase, a leuco dye and 35 peroxidase. IJpon application of a whole blood sample to the sample receptive surface bf the test Stlip, the serum is absorbed ~ 3 ~

into the membrane, thereby initiating conversion of the cholesterol esters to cholesterol, the oxidation of the cholesterol is accomplished by the cholesterol oxidase enzyme, thereby liberating peroxide. The peroxide and leuco dye then interact in S the presenGe of peroxidase to form a highly colored indi~ator which can be monitored either visually or through the use of instrumentation. Additional details relating to this specific reagent system appear in the open literature, see Dappen, G.N., et al., Clin. Chem., Vol. 28, No. 5 (19823, 1159.

A test strip for creatinine can be prepared by absorption into a conditioned membrane of appropriate concentrations of creatinine irninohydrolase and an ammonia indicator (i.e., 15 bromphenol blue). Upon application of a whole blood sample to the sample receptive surface of the test strip, the serum is absorbed into the membrarle, thereby initiating interaction of the creatinine and the enzyme, creatinine amino hydrolase, resulting in the liberation of ammonia. The ammonia thereupon reacts 20 with the indicator and the color development monitored visually or with conventional instrumentation. Additional details relating to this specific reagent appear in the open literature, see for example Tofaletti, J., et al., Clin. Chem., Vol. 29, No. 4 (1983), 684.

It is also contemplated that the dry chemistry reagent systerns of this invention be utilized in a multiple lamina test slide of the type developed by Eastman Kodalc Company of Rochester, N.~.
(hereinafter "Kodak format"). Where a permeable material (i.e.
3 0 spreading layer) is placed in contiguous contact with the sample receptive surface of a treated membrane, such contact will influence (change) the rate and quantity of whole blood/fluid transported through the membrane, and consequently the rate and extent of the reaction mediated by the analyte specific 3 5 components within the membrane. At higher blood analyte levels, the transport of sample across the membrane can result in 3 6 l ~ ~ 7 ~; a~
an overabundance of analyte and thus a foreshortening of the usable range of measurement.

Fig. 7 illustrates the adaptatian of the test strlp of this invention to a displacement immunoassay of the type described in Liotta U.S.
Patent 4,446,232. In the device exempli~ied in Fig. 7, the ~ample receptive surface of the membrane is coated with an enzyme labeled antigen or antibody (hereinafter "enzyme labeled 10 conjugate"). The method of application of the coating to the sample receptive surface insures against penetration of the coating material into the matrix of the membrane. The balance of the immunochemistry reagent system, notably, a chromogenic or fluorogenic substrate for the enzyme, is incorporated into the 15 conditioned membrane, so as to preserve its physical isolation from the surface coating. The contact of the sample with the coating on the surface of the membrane, results in displacement of enzyme labeled material. The displacement of the enzyme labeled conjugate is based upon the dynamic equilibrium which is 20 caused by the presence of an analyte in the sample and the competition with the conjugate for binding to an analyte mimic in the surface coating.

25 The displaced enzyme labeled conjugate, along with a portion of the fluid fraction of the sample, is absorbed in the matrix of the membrane. The enzyme portion of this conjugate interacts with a substrate specific for the enzyme and thereby produces a discernible change in color or fluorescence which is indicative of 3 the analyte of interest. This change can be observed visually, (in the case of a color change) or by instrumentation designed for that purpose.

~c~

Fig. 8(b) depicts a novel membrane/wick composite having unique operational advantages. The wick's function in the composite are two-fold: (a) as an aid to the distribution of sample over the sample receptive surface of the membrane in the area 5 defined by the aperture in the wick; and, (b) the absorption of excess sample, thereby modulating the amount of fluid which is absorbed by the membrane and preventing such excess from inadvertent transfer ~o other surfaces (notably the optical surfaces within a monitoring instrument of the type illustrated in 10 Fig. 9). This limitation of the amount of sample which is absorbed by the membrane, produces a finite end poin~ reaction which can be easily rnonitored. This membrane/wick composite is preferably incorporated within an envelope (22,24) of a test strip (20) of the type illustrated in Fig. 2. The relative orienta~ion of 15 the composite within the envelope is the same as the membrane (3) it would replace. The aperture (26) in the wick (30) of the composite is positioned to coincide wi~h the aperture (26) of the - envelope. I~us, upon application of a whole blood sample to the sample receptive surface of the composite's membrane (3), the 20 blood is essentially uniformly drawn by the wick (120) from its point of application oYer the surface of the membrane, which is framed by the aperture. By facilitating the distlibution of the sample in this manner, th reaction of the analyte with the dry chemistry reagent system proceeds more uniformly, thus, 25 avoiding uneveness in color/indicator development.

The presence of the spreading layer may also be desirable where it is used to laterally transport the whole blood sample from its 30 point of application on the test strip, to the situs of reaction, or where it contains reagents to pretreat or condition the sample prior to its absorption into the membrane. If a contiguous layer is used in conjunction with the membrane, the flow through the membrane may be modulated by changing the concentration of 3 5 the flow control components contained in the impregnating vehicle ~i.e. polyvinyl pyrolidone, polyethylene glycol, etc.). With 38 ~ 7~ ~3~
an increase in ~he concentration of these components, the flow rate across ~he membrane is reduced and the usable range of measurement of the test strip preserved, thus, compensating for ~he presence of a contiguous wicking layer.
S

~koeL~

The Examples which follow fur~her define, describe and illustrate some of the preferred embodiments of the method of preparation, use and evaluation of this dry reagent delivery systems of this invelltion. The equipment and techniques utilized in the preparation, use and evaluation of these dry reagent delivery systems are standard or as hereinbefore described. Parts and percentages appearing in such Examples are by weight unless otherwise stipulated.

.
A dry reagent delivery system is prepared, in accordance with the process of this invention, from the following materials and reagents:
.
(a) Membrane Millipore MF (mixed cellulose acetate-nitrate~ and 3 0 cellulose aceta~e) densi~y 4.9 - 6.5 mg/cm2 porosity 0.01 - 0.45 (sample receptive surface) 3 5 (The porosity ~alue is indica~ive of the differences in pore size from the more dense surface to less dense sur~ace) 3 9 ~ ~ ~ r (b) Indicator - 1% (w/v) aqueous solution deioni~ed water o-tolidine hydrochloride s (c) Glucose Specific Reagent Cocktail glucose o~cidase 48 IU of activity/ml peroxidase 45 IU of activity/ml 0.1 M citrate buffer stabilizer for enzyme - albumin .2% (w/v) conditioning and fIow control agent- polyvinyl pyrolidone 3% (w/v) 15 The membrane is commercially available in rolls of one foot in width. ~or ease of handling, ~he membrane can be cut into strips or squares. Each of the above solutions are prepared fresh ~rom reagent grade ~hemical~ and deionized water.` The membrane is initially contacted with the indicator solution by simply 20 immersing the membrane in a trough containing this ~solution.
The membrane is saturated with the indicatoT solution within 3û
seconds, thereafter ~removed from the solution, drained and dried at room ~emperature or with mild heat.
:

After absorption of the indicator has been completed, this membrane is then ~ontacted, exclusively from the relatively porous surface, wi~h a solution containing the condi~ioning agen$, flow con~ol agent and glucose specific reagent coclctail. The take-3 0 up of this solution by the membrane is effected by simplyfloating membrane on the solution in a shallow tray and con~acting the relatively porous (less dense) surface of the membrane with the surface of ~his solution much like one would blot up a spill with a sponge. Absorption of this solution by the 3 5 membrane is fairly rapid, generally less than 30 seconds. The membrane is then air dried, residual moisture removed by ~ 7~

vacuum drying (lyophilized) and stored to protect it from degradative inMuence light, oxygen, and rnoisture.

S l~k~LE~

The procedures of Example 1 are repeated except for reversal of the order of contact of the indicator solution and the solution 10 containing the conditioning reagent, flow control agent, and glucose specific reagent cocktail with this membrane.

~L~
, : ' .
The procedures of Example 1 are repe,ated except that the membran~ is initially treated with a solution` con~aining the conditioning agent.~ As noted previously in the text of this 20 disclosure, the purpose of such treatment is to modify the internal structure of the membrane, to transform an essentially passive membrane ~o one which actively transports solute. The conditioning of the membrane also decreases its porosity, and -increases the impedance to fluid flow throughout. Accordingly, 25 the porosity gradient a&ross the membrane is essentially eliminated thereby allowing either surface of the membrane to function as a sample receptive surface for a heterogenous fluid sample. The indicator solution and solution containing the flow control agent and the glucose specific reagent cocktail are 3 0 thereafter sequentially imbibed onto the membrane in the manner described in Example 1.

~L 3 ~ 3 3 4~

~k~.~

5 A series of ~est strips, of the configuration of Fig. 2, are prepared incorporating the dry chemistry reagent systems of Examples 1, 2, and 3 respectively. Each category of test strips was then evaluated for rate of sample up-take, sensitivity, uniormity of indicator development and ease of use. The evaluatior~ simply 10 involved the ~ansfer of a drop or two of fresh whole blood to the sample reeeptive surface of the membrane. Test strip performance was then determined by the mollitoring of the observation side o~ the membrane for indicator development.

Both of the test strips of E~amples 1 amd 3 produced results which co~elated well with one another over the range of 50 to ` 600 mg/dl. The ~est s~ip of Example 2 did no~ produce clinically reliable results. This~lack of precision for the test strip of 20 Example 2 was attributed to the inactivation of one or more o f the enzymes of the reagent cocktail by the acidic indicator solution.
I~ is, therefore, unde~stood tha$ the sequence of abso~ption of the various components of the reaent eocktail into the membrane can be dictated by the relative compatibility of the pX of the 25 carrier fluid. Where no such incompa~ibility is present, the order of absorption is not critical; and in fact will generally permit absorption of all of such components ~rom a common (single) solution.

~2 F,~MPLF, ~
Cholesterol Test Strip With Sample Conditioning Pad The dry chemistry reagent system of this invention can be further adapted ~o a cholesterol test strip incorporating both the configuration of Fig. 2 and a sample condition;ng pad. This 10 sample conditioning pad is preferably pre-positioned over the aperture of the membrane of the test strip of ~ig. 2. In one of the commercial embodiments of this device, the sample conditioning membrane is physically integrated/attached to the envelope housing the membrane. The whole blood sample is applied to the 15 sample conditioning pad which promotes the release of the cholesterol from the cholesterol binding protein of the sample.
This sample conditioning pad also promotes a degree of physical separation of the cellular ma$ter from the serum fraction of the sample; howeYer, such physical separation is not believed to be a 20 prerequisite to its effectiveness in the release of cholesterol from the binding protein, nor the ability to express the conditioned sample onto the sample receptive surface of the test strip.

25 ~he dry chemistry reagent delivery system of this ~est strip is prepared in accordance with the procedures described hereinabove in Example 1 from the following mateIials:

~a) Membrane r~
Millipore MF (mixed cellulose acetate-nitrate, and cellulose acetate) density 4.9 - 6.5 mg/cm2 porosity 0.01 - 0.45 (sample receptive surface) - ~ 3 ~

(The porosity value is indicative of the differences in pore size from the more dense surface to less dense surface) (b) Indicator - 1% (w/v) aqueous solution deioni~ed water o-tolidine hydrochloride (c) Cholesterol specific reagent cocktail cholesterol esterase 40 U/ml cholesterol oxidase 40 U/ml peroxidase 148 U/ml 0.1 M Citrate Buffer Stabilizer for en~yme - albumin 0.2% (w/v) Conditioning and flow control agent - polyvinyl pyrolidone 3% (w/v) (d) A sample conditioning pad is prepared by treatment vf a compressible sample adsorbent material with an aqueous salt solution (saline) containing a sample conditioning agent.
Where the sample conditioning pad is a fiberglass mat (re~ention rating of 0.5-3~1m), the conditioning agent is TRITON X-100~ Alternative embodiments of conditioning pad include sponge like materials consisting of cellulose or neoprene which contain 100U Thrombin and physiological salts.

The sample conditioning pad is positioned over the aperture of 3 5 the test strip which exposes the sample receptive surface of the test strip membrane. The whole blood sample is applied to the ~ 3 ~

sample conditioning pad in the same manner as contemplated for use of the other test strips of this invention. After the sample is taken up by this pad, and the interaction of the pad and the sample allowed to go to completion (generally within 30 to 60 seconds), the pad is manually compressed, thereby expressing the conditioned sample onto the sample receptive surface of the membrane. The fluid fraction of the expressed sample is readily absorbed by the dry chemistry reagent system, interacts therewith and produces a color reaction which is readily correlated with color chart/index which correlates the color with a value or level of cholesterol in the sample.

~LE~

The following immunoassays adapt the conditioned membrane technology of this invention to some of the immunoassays which have traditionally been performed in solution or in the classic heterogenous format or in a multi-laminate solid phase format.

1. A test s~ip is prepared by ini~ially coating a thin film containing a quantitative amoullt of peroxidase labeled beta-human chorionic gonadotropin hormone (beta-HCG
conjugate) onto the sample receptive surface of a membrane of the same ~ype used in Example 1. The beta-HCG conjugate is effectively immobilized in this coating by immunochemical binding of ~e antibody portion of the conjugate to a hapten mimic which is also present in the coating. Precautions are taken to insure that the conjugate is not also absorbed into the membrane matrix. Following such surface coating, the balance of this reagent system is absorbed into the membrane by absorption from the 3 5 relative porous side. The sequence of absorption follows the experience gained in the preceding examples, namely, ~ 3 ~

the indicator, o-tolidine (in an acidified vehicle), is absorbed first~ followed by a second solution containing glucose oxidase, citrate buffer glucose and conditioning agent. The format of the ~est strip incorporating the dry chemistry S reagent system, (which is specific for beta HCG~, is the same as that ~escribed for ~ig. 4.

A fresbly voided sample of urine from a pregnant woman is collected in the early morn;ng. This sample is then applied to the sample recepti-~e surface of the test strip by simply dipping the test strip into the urine specimen. The beta-HCG in the urine specimen is thus brought into contact with the coating on the sample receptor s~face of the test s~ip and a portion of the beta-H(:G enzyme conjugate is displaced -~ ~ and binds to the analyte. This displacement of the conjugate ~by the a~alyte allcws the conjugàte to be ~
abso~bed irlto the test strip, where the enzyme portion thereof reacts with ~ its corresporlding substrate ~H202), ultimately r~sulting in oxidation of the o-tolidine (and its conversion to ~a cQlored indicator). The development ~o f color ls, thus, indicative of the presence of analyte in- tlhe sample.
' ~ ~ 2 5 2. A test strip suit~ble for usé in a competitive enzyme immunaassay is prepared by initial absorption of a substrate/color forming composition of Example 5(1) into 3 0 the condit;oned membrane. Also absorbed into the membrane is an enzyme (peroxidase) labelled antigen (i.e.
beta-HCG). A specific quantitative amount of human beta-HCG antibody is coated onto the sample receptive surface of the membrane. A urine sample is then applied to the 3 5 sample receptive surface of the membrane and the beta-HCG antibody on the surtace reacts with the analyte in the , :

4(, ~ 3 ~ ~ ~ '..J j''J
sample. The immunochemical interaction of the analyte with the beta-HCG antibody impedes the absorption of the antibody into the matrix of the membrane. The relative concen~ration of analyte, thus, modulates the intensity of development of the indicator; the h;gher the concentration, the less intense color development. The extent of color development can be monitored visually or through the use of instrumentation.

Alternative indicator syste~s include fluorescent label conjugates (FIA) or radioisotope labelled conjugates (RIA).
In each of these alternate assay formats, indicator concentrations would be monitored with instrumentation.

3. The sol particle immunoassay of Leuvering (U.S. Patent 4,313,734 - is adapted to the conditioned membrane assay format of ~his invention by simply imbibing beta-HCG
labelled colloidal gold particles into the membrane. This reagent is applied to the membrane in quantitative amounts and dried, thereby imparting a uniform color to the membrane surface. An aliquot of sample (i.e. urine) is then applied to the sample receptive surface of the membrane.
The presence of antigen in the sample is rnanifest by an aggregation of the beta-HCG labelled colloidal gold particles, thus, producing a discernible change in color which can be observed visually.

The foregoing Description and Examples have been provided as 3 illustrative of a representative number of the preferred embodiments of this invention. It is not the intent of such Description and Examples to delineate the scope of this invention, which has been reserved to the claims that are set forth herei nafter .

Claims (40)

1. A method for the preparation of a dry chemistry reagent system for analysis of heterogenous fluid samples, said method comprising:
(a) providing a porous membrane having an essentially uniform composition, said porous membrane being characterized as having two planar surfaces and a porosity gradient from one planar surface to the other, the inherent porosity on at least one of said planar surfaces being essentially exclusive of particulate matter on the order of magnitude of cells present in biological fluid samples;
(b) sequentially imbibing into said porous membrane (i) an indicator and (ii) a reagent cocktail specific for reaction with an analyte believed to be present in the fluid sample; and (c) contacting said porous membrane with an absorption effective amount of conditioning agent, said conditioning agent enhancing the absorption characteristics of the porous membrane to fluid samples, said contact of said porous membrane with a conditioning agent occurring either independent of and prior to time to contact of said porous membrane with an indicator or subsequent to contact of said porous membrane with said indicator.

2. The method of claim 1, wherein the porous membrane is conditioned with an absorption effective amount of a conditioning agent selected from the group consisting of albumin, polyvinyl pyrolidone, polyethylene glycol, carbohydrates, carboxymethyl cellulose (water soluble), methyl cellulose, glycerine and polyoxyethylene ethers.

3. The method of claim 1, wherein the porous membrane is cast from a material selected from the group consisting of a cellulose acetate-cellulose nitrate ester, nylon and polysulfone.

4. The method of claim 1, wherein the reagent cocktail is specific for glucose.

5. The method of claim 1, wherein the reagent cocktail is specific for cholesterol.

6. The method of claim 1, wherein the reagent cocktail is specific for urea.

7. The method of claim 1, wherein the reagent cocktail is specific for detection of an antigen or an antibody.

8. The method of claim 7, wherein the reagent cocktail contains an antigen or antibody which is conjugated to a mimic of an analyte.

9. The method of claim 7, wherein the reagent cocktail is specific for detection of hormones, pharmaceutical compounds, drugs of abuse or proteinaceous materials which are capable of evoking an immune response.

10. The method of claim 7, wherein a portion of the reagent cocktail is deposited upon one of the planar surfaces of the porous membrane so as to be retained thereon without substantial penetration into the matrix of the porous membrane.

11. A dry chemistry reagent system for detection of an analyte in a heterogenous fluid sample, said system comprising:
a porous membrane of essentially uniform composition and a porosity gradient from one planar surface thereof to the other, wherein said porous membrane's inherent fluid absorption and distribution characteristics have been modified by imbibing a conditioning agent, an indicator, flow control agent and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform distribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said film so as to enhance the uniformity of absorption and modulate the rate of absorption of the fluid sample and its interaction with the reagent cocktail.

12. The system of claim 11, wherein the porous membrane is conditioned with an absorption effective amount of a conditioning agent selected from the group consisting of albumin, polyvinyl pyrolidone, polyethylene glycol, carbohydrates, carboxymethyl cellulose, methyl cellulose, glycerine and polyoxyethylene ethers.

13. The system of claim 11, wherein the porous membrane is cast from a material selected from the group consisting of a cellulose acetatecellulose nitrate ester, nylon and polysulfone.

14. The system of claim 11, wherein the reagent cocktail is specific for detection of glucose.

15. The system of claim 11, wherein the reagent cocktail is specific for detection of cholesterol.

16. The system of claim 11, wherein the reagent cocktail is specific for detection of urea.

17. The system of claim 11, wherein the reagent cocktail is specific for detection of an antigen or an antibody.

18. The system of claim 17, wherein the reagent cocktail contains an antigen or antibody which is conjugated to a mimic of an analyte.

19. The system of claim 17, wherein the reagent cocktail is specific for detection of hormones, pharmaceutical compounds, drugs of abuse or proteinaceous materials which are capable of evoking an immune response.

20. The system of claim 17, wherein a portion of the reagent cocktail is deposited upon one of the planar surfaces of the porous membrane so as to be retained thereon without substantial penetration into the matrix of the porous membrane.

21. A rapid analytical method for screening a heterogenous fluid sample for an analyte of interest, comprising:
(a) providing a dry chemistry reagent system comprising a porous membrane of essentially uniform composition and a porosity gradient from one planar surface thereof to the other, wherein said porous membrane's inherent fluid absorption characteristics have been modified by sequentially imbibing a conditioning agent, an indicator, flow control agent and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform distribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said porous membrane so as to modu-late both the rate and the uniformity of absorption of the fluid sample and its interaction with the reagent cocktail;
(b) applying a heterogenous fluid sample to the sample receptive surface of the bibulous medium of the reagent system; and (c) monitoring the surface of the bibulous medium opposite to the sample receptive surface for a change of color or fluorescence or for the development of color or fluorescence.

22. The analytical method of claim 21, wherein the porous membrane is conditioned with an absorption effective amount of a conditioning agent selected from the group consisting of albumin, polyvinyl pyrolidone, polyethylene glycol, carbohydrates, carboxymethyl cellulose, methyl cellulose, glycerine and polyoxyethylene ethers.

23. The analytical method of claim 21, wherein the porous membrane is cast from a material selected from the group consisting of a cellulose acetate-cellulose nitrate ester, nylon and polysulfone.

24. The analytical method of claim 21, wherein the reagent cocktail is specific for detection of glucose.

25. The analytical method of claim 21, wherein the reagent cocktail is specific for detection of cholesterol.

26. The analytical method of claim 21, wherein the reagent cocktail is specific for detection of urea.

27. The analytical method of claim 21, wherein the reagent cocktail is specific for detection of an antigen or an antibody.

28. The analytical method of claim 27, wherein the reagent cocktail contains an antigen or antibody which is conjugated to a mimic of an analyte.

29. The analytical method of claim 27, wherein the reagent cocktail is specific for detection of hormones, pharmaceutical compounds, drugs of abuse or proteinaceous materials which are capable of evoking an immune response.

30. The analytical method of claim 27, wherein a portion of the reagent cocktail is deposited upon one of the planar surfaces of the porous membrane so as to be retained thereon without substantial penetration into the matrix of the porous membrane.

31. A test kit for analysis of a heterogenous fluid sample, said kit comprising:
(a) dry chemistry reagent system comprising a porous membrane of essentially uniform composition and a porosity gradient from one planar surface thereof to the other, wherein said porous membrane inherent fluid absorption and distribution characteristics have been modified by sequentially imbibing a conditioning agent, an indicator and reagent cocktail into its matrix, the effect of such absorption being to effect an essentially uniform distribution of indicator, flow control agent and reagent cocktail within the porous membrane thereby enhancing the uniformity of internal structure of said film so as to modulate both the rate and uniformity of absorption of the fluid sample and its interaction with the reagent cocktail; and (b) a standard for comparison with the indicator of the dry chemistry reagent system.

32. The test kit of claim 31, wherein the porous membrane is conditioned with an absorption effective amount of a conditioning agent selected from the group consisting of albumin, polyvinyl pyrolidone, polyethylene glycol, carbohydrates, carboxymethyl cellulose, methyl cellulose, glycerine and polyoxyethylene ethers.

33. The test kit of claim 31, wherein the porous membrane is cast from a material selected from the group consisting of a cellulose acetatecellulose nitrate ester, nylon and polysulfone.

34. The test kit of claim 31, wherein the reagent cocktail is specific for detection of glucose.

35. The test kit of claim 31, wherein the reagent cocktail is specific for detection of cholesterol.

36. The test kit of claim 31, wherein the reagent cocktail is specific for detection of urea.

37. The test kit of claim 31, wherein the reagent cocktail is specific for detection of an antigen or an antibody.

38. The test kit of claim 37, wherein the reagent cocktail contains an antigen or antibody which is conjugated to a mimic of an analyte.

39. The test kit of claim 37, wherein the reagent cocktail is specific for detection of hormones, pharmaceutical compounds, drugs of abuse or proteinaceous materials which are capable of evoking an immune response.

40. The test kit of claim 37, wherein a portion of the reagent cocktail is deposited upon one of the planar surfaces of the porous membrane so as to be retained thereon without substantial penetration into the matrix of the bibulous film.