SEALED REAGENT MATRIX

Abstract: At least one edge of each reagent matrix on a reagent test device is sealed using a wax/adhesive mixture such that liquid present in the reagent matrix material is retained therein and prevented from running over into another reagent matrix area present on the same reagent test device.

Description: FIELD OF THE INVENTION The present invention relates to sealing the edges of reagent matrix material and, more particu­ larly, to reagent matrix material which has had a sealing composition applied to its edges to prevent or minimize cross-contamination of reagents during use. BACKGROUND OF THE INVENTION The art of analytical chemistry has been greatly advanced since biochemistry began emerging as a primary scientific frontier, requiring in­ creasingly sophisticated analytical methods and tools to solve problems. Likewise the medical profession has lent impetus to the growth of analytical chemistry, with its desiderata of both high precision and speed in obtaining results. To satisfy the needs of the medical profession as well as other expanding technologies, such as the brewing industry, chemical manufacturing, etc., a myriad of analytical procedures, compositions and apparatus have evolved, including the so-called "dip-and-read" type reagent test device. Reagent test devices enjoy wide use in many analytical applications, especially in the chemical analysis of biological fluids, because of their relatively low cost, ease of usability, and speed in obtaining results. In medicine, for example, numerous physiological functions can be monitored merely by dipping a reagent strip test device into a sample of body fluid, such as urine or blood, and observ­ ing a detectable response, such as a change in color or a change in the amount of light reflected from or absorbed by the test device. Many of the "dip-and-read" test devices for detecting body fluid components are capable of making quantitative or at least semiquantitative measurements. Thus, by measuring the response after a predetermined time, an analyst can obtain not only a positive indication of the presence of a particular constituent in a test sample, but also an estimate of how much of the constituent is present. Such test devices provide the physician with a facile diagnostic tool as well as the ability to gage the extent of disease or of bodily malfunction. Illustrative of such test devices currently in use are products available from the Ames Division of Miles Laboratories, Inc. under the trademarks CLINISTIX, MULTISTIX, KETOSTIX, N-MULTISTIX, DIASTIX, DEXTROSTIX, and others. Test devices such as these usually comprise one or more carrier matrices, such as absorbent paper having incor­ porated therein a particular reagent or reactant system which manifests a detectable response, e.g., a color change, in the presence of a specific test sample component or constituent. Depending on the reactant system incorporated with a particular matrix, these test devices can detect the presence of glucose, ketone bodies, bilirubin, urobilinogen, occult blood, nitrite, and other substances. A specific change in the intensity of color observed within a specific time range after contacting the test device with a sample is indicative of the presence of a particular constituent and/or its concentration in the sample. Some of these test devices and their reagent systems are set forth in U.S. Patent Nos. 3,123,443; 3,212,855 and 3,814,668. Thus, it is customary for reagent test devices to contain more than one reagent bearing carrier matrix, in which each reagent bearing carrier matrix is capable of detecting a particular consti­ tuent in a liquid sample. For example, a reagent test device could contain a reagent bearing carrier matrix responsive to glucose in urine and another matrix responsive to ketones, such as acetoacetate, which is spaced from, but adjacent to, the glucose responsive matrix. Such a product is marketed by the Ames division of Miles Laboratories, Inc. under the trademark KETO-DIASTIX. Another reagent test device marketed by the Ames Division of Miles Laboratories, Inc., N-MULTISTIX, contains eight adjacent reagent incorporated matrices providing analytical measurement of pH, protein, glucose, ketones, bilirubin, occult blood, nitrite, and urobilinogen. Despite the obvious, time-proven advantages of such multiple reagent test devices as these, misuse can result in misinformation. These multiple analysis tools comprise complex chemical and catalytic systems, each reagent matrix containing an unique reactive system, responsive to its particular analyte. Thus, it is possible, if the reagent test device is misused, for chemicals to be transported by the liquid sample being analyzed from one carrier matrix on the reagent test device to another. Should this happen it is possible for reagents from one carrier matrix to interfere with those of the other so contacted causing unreliable results. Although it is common in the reagent test device industry to provide detailed instructions of how this problem can be minimized, i.e., directions for properly manipulating the reagent test devices by blotting excess fluid, nevertheless ignorance or disregard of these instructions could permit reagents from one matrix to run over onto an adjacent one. Cross-contamination can result in false results. It is the prevention of this "runover" problem that the present invention is primarily directed. The elimination of runover has been long sought after and the present discovery, which is the cumulation of an extensive research effort, provides a very effective solution to this problem. DISCUSSION OF THE PATENT LITERATURE The patent literature is replete with accounts of myriad attempts at curtailing runover, the great bulk of the emphasis being directed to two basic concepts: the absorbance of runover liquid by bibulous layers placed beneath the reagent-bearing layers of reagent test devices; and the use of hydrophobic barriers between the spaced matrices. The former has met with moderate success, whereas the latter approach has not. Of the multilayer type reagent test devices, U.S. Letters Patent No. 4,160,008 describes a test device in which the carrier matrices containing reagent formulations are provided with adsorbent underlayers which are separated therefrom by sample impervious barrier layers. Each matrix thus forms the upper layer of a laminate composite in which the barrier layer is disposed between the matrix and the adsorbent base layer, the composite being fixed to a suitable support such as a plastic substrate. When the test device is dipped into the liquid sample the portion of sample which would otherwise runover from one matrix to another is largely adsorbed into the underlayer of the latter through the exposed sides, the barrier layers of the composite preventing the adsorbed runover from reaching the upper reagent layers. U.S. Letters Patent No. 4,301,115 discloses and claims a test device comprising a base support member coated with a hydrophobic barrier layer to which a plurality of spaced apart reagent matrices are affixed. This approach virtually eliminates cross-contamination between adjacent reagent areas of multiple reagent test devices, but requires an extra step of applying hydrophobic material to the base support member of the reagent test device. With respect to the development and use of barriers and/or barrier materials between reagent matrices, the patent literature is replete with teachings, which in theory, at least, would seem to overcome the runover problem. U.S. Letters Patent No. 3,418,083 discloses an indicator-impregnated adsorbent carrier matrix treated with wax, oil or similar "hydrophobic" agents. It is stated that when a sample of blood is placed on the resulting reagent test device, only colorless liquid components permeate it, the proteinaceous, colored blood components remain on the surface where they can be removed. Thus, it is taught that the liquid portion bearing the analy­ sate permeates the reagent matrix pad and color interference is precluded. Still another patent, U.S. Letters Patent No. 3,001,915, describes an adsorbent paper reagent test device having spaced reagent-impregnated test areas for more than one sample component, each such area being separated from the other reagent-impreg­ nated test area by a nonadsorbent barrier portion. The barrier is provided by impregnation of the paper strip with materials such as polystyrene, rosin, paraffin and various cellulose esters. The reagent strip is prepared, according to the refer­ ence, by impregnating a portion of the paper strip with a glucose sensitive reagent system. When dry, a solution of one or more of the barrier materials is applied to the paper adjacent a glucose sensi­ tive portion. After further drying a protein sensitive reagent system is applied and the process is repeated with alternate applications of reagent and barrier solutions with drying steps inbetween. Yet an earlier patent, U.S. Letters Patent No. 2,129,754, describes the impregnation of filter paper with paraffin wax whereby specific areas are left unimpregnated and these areas are treated with indicator systems for a particular analyte. In U.S. Letters Patent No. 3,006,735 the concept of barrier material impregnated between reagent areas of a reagent test device is carried one step further by providing successive reagent areas responsive to different degrees of water hardness. Water repellent material, such as oils, waxes, silicones, and printer's varnish, is impreg­ nated between these reagent test areas. Like the proceeding two patents this citation is restricted to paper or like bibulous material wherein reagent and barrier material alike are impregnated sequen­ tially along the test device. In European Patent Application No. 126 357, various materials, including waxes, are suggested for sealing the edges of reagent matrix material such that liquid present in the reagent matrix will be retained therein and prevented from running over into another reagent matrix area present on the same reagent test device. U.S. Letters Patent Nos. 3,011,874 and 3,127,281 teach the use of hydrophobic barrier materials impregnated in part of a reagent test device in order to separate one reagent area from another and thereby avoid contamination. Yet another patent which mentions the separa­ tion of indicator reagent sites by the use of nonadsorbent or hydrophobic materials is U.S. Letters Patent No. 3,964,871. Currently marketed reagent test device prod­ ucts, for the most part, contain reagent impreg­ nated matrices affixed to hydrophobic organoplastic material. Thus, the multiple reagent test device known as N-MULTISTIX contains eight different reagent impregnated matrices mounted on a polysty­ rene film. Since polystyrene is hydrophobic, the reagent strip can be said to have hydrophobic interstices between adjacent matrices. Despite lip service given by literature accounts to the elimination of runover, the fact remains that the problem continues to exist. The approaches disclosed in U.S. Letters Patent Nos. 4,160,008 and 4,301,115 have come the closest to eliminating the runover problem. Prior attempts using wax, oils, silicones, and the like materials, have not curtailed runover to a clinically significant extent; and what modest advances have been made are more than offset by serious drawbacks inherent to such attempts. For example, applying hydrophobic material only at reagent area interstices embodies technical prob­ lems, especially when compared with the current techniques for manufacturing dip-and-read reagent test devices. Besides the obvious extra steps required by interstitial application, there is the danger of some of the hydrophobic material overlap­ ping the reagent area thereby interfering with the paramount purpose of the reagent test device. Moreover, none of the substances taught by the prior art provides a suitable surface for adhesion. Even if the above shortcomings were not prohibitive enough, the prior art hydrophobic substrates lack a degree of hydrophobicity required to prevent runover. They do not provide a suffi­ cient contact angle to achieve the required hydro­ phobicity, nor do they provide a suitable surface for binding either the adsorbent matrices or the reagents themselves, where they are coated directly on the substrate surface. The present invention virtually eliminates cross-contamination between adjacent reagent areas of multiple reagent test device matrices. The results are truly incontrovertible and the success achieved in solving this problem compares favorably with the use of a hydrophobic barrier layer, as described in U.S. Letters Patent No. 4,301,115. Moreover, the present invention does not require the presence of an additional layer applied to the substrate of reagent test devices. The present invention, involving the sealing of one or both facing edges of a reagent matrix area, can be accomplished quickly and accurately. SUMMARY OF THE INVENTION An object of the present invention is to seal one or both facing edges of each reagent matrix of a reagent strip test device containing multiple carrier matrices in a way which prevents or sub­ stantially eliminates runover problems. Another object of the present invention is to substantially eliminate runover problems by sealing one or both facing edges of each reagent matrix during the production of reagent test devices in a manner which does not interfere with the impreg­ nated reagents in any individual carrier matrix. Still another objection of the present inven­ tion is to provide an inexpensive and effective means of eliminating or materially reducing run­ over. In accordance with the present invention, one or both facing edges of each reagent matrix are sealed with a specially formulated mixture of wax and adhesive. The specially formulated mixture consists of a high viscosity hot-melt adhesive combined with a wax which can be heated to a temperature of between approximately 90°C and 150°C and applied by a conventional hot-melt machine or other suitable means at one or more edges of reagent ribbon matrix material. Normally, the mixture is applied after the matrix material has been laminated onto a suitable substrate. DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, reagent matrix material is sealed with a specially formulated sealing mixture applied to one or both facing edges of each reagent matrix material. By applying sealing material only to the edges of the reagent matrix, reagent in the impregnated matrix is not affected. Accordingly, upon drying, the sealing material effectively seals one or more opposing ends or edges of the reagent matrix material and does not interfere with the reaction which takes place when the resulting reagent test device is contacted with liquid, such as a body fluid or an industrial liquid, to be tested. The sealing material utilized to seal the edges of the reagent matrix material is a specially formulated mixture of wax and a high viscosity hot-melt adhesive. Broadly, the ratio of wax to adhesive can be from 1:1 to 1:4. Preferably, however, the ratio of wax to adhesive is 1:3. In addition to water-repellency, the sealing material has the characteristic of reasonable viscosity at elevated temperatures such that it can be easily applied to the edges of reagent ribbon and then quickly dried at room temperature or a slightly elevated temperature and remain solid over the normal temperature range in which reagent test devices are used. Clearly, no interaction must occur between the sealing material and the re­ agent(s) present in the reagent ribbon. Waxes which are especially useful for use in the sealing material formulations are thermo­ plastic, water repellent, smooth in texture, nontoxic, and have freedom from any objectionable odor or color. Major types of waxes which can be employed include natural waxes, such as animal wax, beeswax, spermaceti, lanolin, shellac wax; vegeta­ ble waxes, such as carnauba, candelilla, bayberry, sugar cane; mineral waxes, such as fossil or earth waxes, including ozocerite, ceresin, montan; and petroleum waxes, such as paraffin, microcrystal­ line, petrolatum; as well as synthetic waxes such as ethylenic polymers and polyolether-esters including Carbowax, sorbitol and chlorinated napthalenes such as Halowax and other hydrocarbon waxes. A preferred wax is the WW0404 wax from H. B. Fuller Company of Kalamazoo, Michigan, which has the following characteristics: Melting point (ASTM D127) 82°C ± 4%, hydrophobic, inert, bendable and not tacky when dry. The congeal point (ASTM D938) is 76°C ± 4%, viscosity (Brookfield Thermocal) is 17.5 cps 93°C, and color (ASTM D1500) is 1.0 Saybolt. The hot-melt adhesive is also a thermoplastic material which can be a polyolefin, an olefin copolymer, polyester or polyamide. Among the polyolefins, polyethylene and polypropylene are particularly applicable. Copolymers of ethylene and vinylacetate are also useful. Polyamide hot-melt adhesives can be used, but tend to be more expensive. Polyester adhesives are also fairly high in price, but have good solvent resistance. Advantageously, the adhesive employed must have a fast set time. A particularly preferred hot-melt adhesive is the Eastobond hot-melt adhesive A-3 which is made by Eastman Kodak Company, Kingsport, Tennessee. This adhesive has a thermal con­ ductivity at 33°C and 10⁻⁴ Cal/cm-sec. of 7.1; a heat of fusion of 13.4 calories per gram and a specific heat at 25°C of 0.58 Cal/gram. The Eastobond adhesive has a viscosity at application temperature of approximately 2200 centipoises. The combined wax/adhesive formulation ideally has a softening point in excess of 70°C and no component melting below 80°C. The formulation is capable of drying quickly, i.e., in about 10 seconds, under ambient conditions and is not tacky when cold. The resulting mixture is hydrophobic, inert, slittable, colorless, insoluble in water and adheres readily to both paper and polystyrene. The reagent ribbon or matrix material can be formed from any suitable material. U.S. Letters Patent No. 3,846,247 teaches the use of felt, porous ceramic material and woven or matted glass fibers. Additionally, U.S. Letters Patent No. 3,552,928 teaches the use of wood, cloth, sponge material and argillaceous substances. The use of synthetic resin fleeces and glass fiber felts as carrier matrix is suggested in British Patent No. 1,369,139. Another British Patent, No. 1,349,623, proposes the use of light permeable meshwork of thin filaments as a cover for an underlying paper matrix. Polyimide fibers are taught in French Patent No. 2,170,397. Notwithstanding these suggestions, however, the material predominantly used in the art as a carrier matrix and that which is especially useful in the present invention is bibulous paper, such as filter paper. As indicated above, the reagent ribbon is normally impregnated with reagent material prior to the sealing of the edges of the reagent ribbon in accordance with the present invention. In fact, in a preferred embodiment the reagent ribbon is attached to a card of suitable substrate material such as Trycite (polystyrene) using double faced adhesive tape such as Double Stick, available from the 3M Company, prior to the application of the sealing material to one or more edges of the reagent ribbon. Thus, following conventional techniques multiple reagent ribbons are applied to a substrate card and then a hot-melt machine, such as the Nordson hot-melt device, which is manufac­ tured and sold by the Packaging & Assembly Division of Nordson Corporation, is used to apply the specially formulated mixture of wax and adhesive to one or both of the exposed edges of the reagent ribbon. While the specially formulated wax/­ adhesive mixture can be applied to both of the exposed edges of the reagent ribbons, it has been found that normally the wax/adhesive mixture does not have to be applied to both sides of each reagent ribbon provided that the wax/adhesive mixture is applied to the same side of each matrix such that at least one barrier is formed between each of the resulting matrices on a reagent test device. Following application of the hot-melt admixture, the card containing reagent ribbons adhesively bound thereto is then cut widthwise in conventional manner to form reagent test devices. These reagent test devices can measure, for example, 8 x 0.5 centimeters having squares of reagent laden carrier matrices 0.5 centimeter on a side at one end thereof; the other end serving as a handle for the reagent test device. Since at least one edge of the reagent matrix material on each matrix pad is sealed by the sealing material in accordance with the present invention, liquid runover problems and the problems created by runover are effectively eliminated or substantially reduced. EXAMPLE Using a Nordson hot-melt machine, a specially formulated mixture of wax and adhesive containing 25 percent of H. B. Fuller's WW04040 wax and 75 percent of Eastman Kodak's A-3 hot-melt adhesive was heated to 93°C and then applied using a 0.0635 centimeter orifice nozzle to the edge of a con­ tinuous reagent impregnated filter paper ribbon which had been attached by means of double backed adhesive to polystyrene substrate material. By varying the composition of the reagents so as to have a reagent test device with alternating pads of reagents suitable for the analysis of urobilinogen and nitrite and by applying the wax/adhesive admixture to only one side of each of the matrices, it was found to be possible to achieve 95 percent elimination of runover between the urobilinogen and nitrite reagent areas. Traditionally, the reagents for determination of these two analytes create the worst runover problem when they are both on the same test device. Thus, utilizing the present procedure, it is possible to apply reagent areas for measuring urobilinogen and nitrite adjacent to each other on the same reagent test device and it is no longer necessary to separate these reagent areas on the reagent test device or utilize more elaborate and costly means for overcoming the runover problem between adjoin­ ing spaced carrier matrices. In contrast to the application of wax alone along the edges of reagent matrix material, the test devices prepared in accordance with the present invention have improved adhesion which is important because of the necessity to bond or adhere to different types of materials, e.g., polystyrene and paper. Moreover, the softening point of the wax/adhesive admixture is substantial­ ly improved over that of the wax alone. This is important because of the melting problem which can occur during shipment of reagent test devices when the containers in which the reagent test devices are stores are subjected to temperatures of 66° centigrade or higher. A stability problem has occurred when waxes were used to seal reagent matrix material and the resulting test devices were subjected during shipment to relatively high temperatures which would cause the wax to soften or melt and then spread into areas which interfered with the use of the test devices. In extreme cases, the melting wax can even bind with other test devices in the shipping container. The specially formulated wax/adhesive admixture of the present invention overcomes these problems in addition to overcoming the runover problem between adjoining spaced carrier matrices. From the foregoing, it will be seen that this invention is well adapted to attach all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the system. The wax/adhesive admixture represents a marked improvement over the use of wax alone in terms of both ease of application and effectiveness. For example, the present invention has the advantages of convenience, simplicity, relative inexpensiveness, positiveness, effective­ ness, durability, accuracy and directness of action. The wax/adhesive mixture adheres firmly at the point of application and does not spread or interfere with the reagents present in the matri­ ces. The invention substantially overcomes prob­ lems associated with runover which have been a continuing and long felt problem with multiple reagent test devices. The invention provides a very effective, simple and inexpensive way of eliminating or materially reducing the runover problem. In addition, the present invention can effectively be utilized in conjunction with conven­ tional techniques, or methods for forming reagent test devices. There is no extra layer which must be applied to reagent test devices in order to control the runover problem. Moreover, the present invention could, if desired, be used in conjunction with other techniques found useful to control the runover problem. Thus, the present invention could be utilized in conjunction with techniques in the prior art which rely on the use of hydrophobic barrier layers affixed to reagent test devices. Obviously, many other modifications and variations of the invention as hereinbefore set forth can be made without departing from the spirit and scope and thereof.

Claims: 1. A reagent test device comprising multiple reagent carrier matrices attached in spaced rela­ tionship to one side of the substrate, said reagent carrier matrices being impregnated with a wax/­ adhesive admixture in an amount sufficient to seal at least one facing edge on each carrier matrix to prevent liquid runover between adjoining spaced carrier matrices, said wax/adhesive admixture having a softening point greater than 70°C and a melting point greater than 80°C. 2. The test device of claim 1 in which the carrier matrix is filter paper. 3. The test device of claim 1 in which the substrate is polystyrene. 4. The test device of any of claims 1 to 3 in which the wax and adhesive are present in the admixture in the ratio of 1:1 and 1:4. 5. The test device of any of claims 1 to 4 in which the water repellent material is an admixture of wax and adhesive in the ratio of 1:3. 6. The process of sealing at least one facing edge of each reagent matrix area on a reagent test device containing multiple carrier matrices to substantially eliminate runover between adjoining spaced carrier matrices, which comprises applying an admixture of wax and adhesive as a hot-melt along each edge of reagent carrier matrix material which is to be sealed, said wax/adhesive admixture having a softening point greater than 70°C and a melting point greater than 80°C. 7. The process of claim 6 in which the carrier matrices are filter paper. 8. The process of claim 6 in which the substrate is polystyrene. 9. The process of claim 6 in which the carrier matrix material is filter paper which is laminated to polystyrene substrate prior to the time of applying the wax/adhesive admixture.

Inventors: SIDDIQI, SULTAN M., STEMM, PATRICK
Applicants: MILES INC.
Application year: 1986
Main classification: G01N33
IPC codes: G01N31, G01N33