ANALYTICAL TEST DEVICE

Abstract: An analytical device (10) for the qualitative and/or quantitative determination of an analyte in a liquid test sample, comprises a base (12) supporting a porous member (16) which has an analyte-responsive substance therein, the substance being capable of undergoing a detectable response to the presence and/or concentration of analyte in the test sample. A cover (18) integral with the base (12) is provided with a reaction well (28) formed therein for storing a dried reaction component (34) and for receiving the liquid test sample to form (with the reaction component) a liquid reaction mixture therein. The reaction well has a passage (30) which is normally spaced from the porous member (16) and effectively closed to transfer therethrough of the reaction mixture, but which is movable towards the porous member effectively to open the passage to allow flow therethrough of the reaction mixture into the porous member (16). The analyte responsive substance in the porous member will undergo a detectable response to any analyte present in the liquid reaction mixture. The base can be provided with a suitable viewing port (54) to permit monitoring of the detectable response generated in the porous member.

Description: This invention relates to an analytical test device for qualitative and/or quantitative determination of an analyte in a liquid test sample. The device is particularly useful for performing dry chemistry analysis of aqueous fluids, i.e. for analyses carried out using chemical reagents contained in "dry-to-the-touch" devices. An increasingly large number of analytical tests, procedures and analyses, i.e. assays, are performed each day on many kinds of liquid samples, including aqueous biological fluids such as blood, serum, urine, cerebrospinal fluid and the like. Various methods have been developed for conducting such analyses, including those known in the art as dry chemistry analysis techniques. A widely used dry chemistry analytical element which is very readily adaptable for use in automated sample liquid analysis systems, is the multilayer test element. Traditional multilayer analysis techniques rely on film technology wherein reagents are applied to a transparent film supported in layers. Such multilayer devices, which are well known in the art, may consist of one or more spreading layers, reaction layers, separation layers and detection layers superimposed one on the other, according to the analyte to be detected and the method of analysis used. These multilayer analytical elements are typically custom designed to the particular assay to be performed. That is, there is generally no generic structure that can be adopted for such an analytical element, and the number of different analytes that can be detected using a multilayer element of a particular construction is limited. In general, to perform an assay using a typical multilayer test element, a sample of body fluid is applied to a spreading layer to ensure even distribution of the sample to an underlying reaction layer which may contain a reagent component. This liquid sample and first reagent mixture then passes into a second underlying layer for reaction with additional reagent components. Since the reagent-containing layers may be in contact with each other, there is a risk of cross-migration of their respective reagent components and hence for unintentional contamination. Generally, devices so constructed do not allow for the performance of sequential operation. The liquid sample and liquid sample reagent mixture will flow from one layer to the next unless a separate timing layer is provided therebetween. The timing layer retains for a certain period of time the liquid in the top layer until the reaction is substantially complete, and then releases the resulting reaction product to diffuse into the underlying layer. The desirability of maintaining the reagent-containing layers in spaced relationship to each other to minimize contamination and to provide some control over the timing of the assay sequence has been recognized in the art. Multilayer analytical devices have been provided wherein a liquid test sample contacts a reagent in a first reagent layer, with this layer adapted to be brought thereafter into contact with a second layer by moving the first and second layers into fluid contact with each other when a certain stage in the reaction is reached. Examples are shown in U.S. patent specification nos. 4,258,001 and 4,357,363 (Eastman Kodak Company). In one embodiment, the analytical element contains two layers or zones carried on a support. The zones are initially spaced apart by a spacer means. Under conditions of use, these zones are brought into contact such as by application of suitable compressive force to the upper zone which causes the pressure-deformable spacer means to deform resulting in the upper zone being moved into fluid contact with the lower zone. There is no indication in either reference, however, as to whether the zones are brought into fluid contact after the reaction sequence is completed, although the language in the respective documents suggests fluid contact between the zones occurs substantially at the time of sample application. The need to control the sequential interaction of the test sample with various reagents, while being important in some chemical assays, is of necessity when considering immuno-chemical analysis wherein the antibodies, enzymes and substrates in the reagents must be segregated during storage, and introduced into the sample or the reaction mixture at the proper time and in the proper sequence. While various proposals have been made with respect to multilayer analysis elements utilizing chemical reactions, only a few recent proposals have been made with respect to such multilayer analysis films in which reagents for immunological reactions are incorporated (see, for example, U.S. patent specification no. 4,587,102 and the references cited therein). When one attempts to apply immunological reaction techniques to conventional multilayer analysis films, it is difficult to obtain satisfactory analysis data due to problems inherent to immunological analysis as discussed in this reference. In the aforementioned U.S. patent specification no. 4,587,102, a dry type multilayer analysis element for assaying a concentration of a specific component utilizing a competitive immunological reaction is described. The analysis element contains a detection element comprising a detection layer which received a labelled complex formed as a result of the competitive immunological reaction, and provides an optically detectable change dependent upon an amount of the labelled complex of the specific component. Further provided on the detection layer is a reaction layer comprising a fibrous porous medium containing fine particles. While this device attempts to address the problems inherent with immuno-chemical analysis utilizing multilayer analytical elements, it is still a comparatively complex structure requiring many different components and is utilizable only for a limited number of different assay protocols. U.S. patent specification no. 4,717,656 describes a device for chemical analysis which consists essentially of a series of interconnected segments wherein a sample to be tested is contacted with reagents reacting with the sample to form a detectable substance which in turn is detected for a qualitative or quantitative determination. Essentially, the device is a test kit for performing an analysis wherein all the chemically active parts which are necessary for carrying out the analysis are built into the device. These chemically active parts are arranged or mounted in such a way that they are connected with the sample and each other by a simple folding system. While this device permits the timed, sequential performance of the assay, the physical manipulations of the various segments as required in this device make it totally unusable in an automated analysis system. U.S. patent specification no. 4,288,228 discloses whole blood analysis and diffusion apparatus therefor. In one embodiment, a precise aliquot is obtained by a carefully controlled cross-diffusion between the porous media via a molecular diffusion switch. The molecular switch achieves accurately timed diffusion of substances from one medium to another, such that an amount (aliquot) of material may be accurately and precisely transferred. The molecular switch is comprised of an impermeable layer which acts as a barrier or isolating means between two porous media. Preferably, this impermeable layer is an immiscible fluid (eg. gas or liquid) which is easily displaced from between the porous media, and then restored therebetween. Although providing for a timed reaction, this device would not be readily adaptable for use in an automated clinical analyzer. We have now made a new analytical device for dry chemistry analysis, whereby the reagents can be kept apart until the user wishes to mix them, and which is of simple and inexpensive construction but reliable. In one aspect, the invention provides an analytical device for the qualitative and/or quantitative determination of an analyte in a liquid test sample, said analytical device comprising: a) a base; b) a porous member received in said base; c) at least one analyte responsive substance dispersed throughout said porous member which substance undergoes a detectable response to the presence and/or concentration of said analyte; d) a reaction component; e) a cover integral with said base; f) a reaction well in said cover for storing said reaction component and for receiving said liquid test sample whereby said liquid test sample and said reaction component can form a liquid reaction mixture within said reaction well; g) passage means in said reaction well for transferring said reaction mixture therethrough, said passage means being spaced from said porous member and effectively closed to transfer therethrough of said reaction mixture, said passage means being selectively movable toward said porous member effectively to open the passage to allow said reaction mixture to flow therethrough to said porous member, whereby said analyte responsive substance in said porous member can undergo a detectable response to said analyte present in said liquid reaction mixture; and h) said base includes an observation port to expose said porous member to observation for any detectable response of said analyte responsive substance thereon. The invention also includes a method of qualitative and/or quantitative determination of an analyte in a liquid test sample, said method comprising the steps of: a) depositing an aliquot of said liquid test sample in the reaction well of an analytical device of the invention; b) permitting said aliquot of liquid test sample and said reaction component to form a liquid reaction mixture within said well; c) displacing said passage means toward said porous member to effectively open the passage and allow the reaction mixture to flow therethrough to said porous member, whereby said analyte responsive substance will undergo a detectable response to any said analyte present in said liquid reaction mixture; d) detecting and/or measuring the detectable response produced by said analyte responsive substance; and optionally e) comparing the detectable response produced by said test sample with the detectable response produced by a series of standard compositions containing known amounts of said analyte. In the analytical devices of the invention, the base supports a reagent containing means which is a porous member preferably having dispersed throughout at least one analyte responsive substance in a dry state. This substance is designed to undergo a detectable response to the presence and/or concentration of the particular analyte in the test sample. Integral with the base is a cover or support member adapted for storing a reaction component therein. This reaction component can include a substance which physically changes the sample, such as a cytolytic agent, to release an analyte for detection, or may be a reagent component which is responsive to the analyte to form a reaction product, which when coming into contact with at least one analyte responsive substance in the porous member, generates a detectable response. The reaction component which is preferably in the dry state, is retained in a reaction well in the cover which is adapted to receive the liquid test sample deposited on the analytical device whereby the liquid test sample and the dry reaction component mix to form a liquid reaction mixture within the reaction well. The reaction well includes a passage means therein for selectively transferring the reaction mixture therethrough. This passage means is normally spaced from the porous member and is effectively closed to transfer therethrough of the liquid reaction mixture held in the reaction well, and is selectively movable toward the porous member to effectively open to allow passage therethrough of the reaction mixture to the porous member whereby the analyte responsive substance will undergo a detectable response to the analyte present in the liquid reaction mixture. The mixture means may be at least one opening in the reagent well with the passage means and the reagent well dimensioned such that the surface tension of the liquid reaction mixture with the walls of the opening and the reaction well prevents the liquid reaction mixture held in the reaction well from transfer through the passage means to the porous member. When the passage means is moved into engagement with the porous member, the liquid reaction mixture held within the reaction well by surface tension is drawn through the passage by capillary attraction. In another configuration, the passage means includes a transverse or bottom wall in the reaction well which contains one or more openings that are normally substantially closed. As the passage means is moved into engagement with the porous member, the openings in the transverse wall open to permit the flow of liquid contained in the reaction well into the passage means. The openings may be arcuate or radial slits in the transverse wall. The base is preferably provided with a suitable viewing port to permit monitoring of the detectable response generated as a result of the at least one analyte responsive substance interacting with the analyte in the test sample. Such a detectable response may be detected by appropriate photometric or colorimetric apparatus. By measuring the detectable response produced by the analyte responsive substance and comparing the detectable response so produced with the detectable response produced when the analysis is conducted with a series of standard compositions containing known amounts of analyte, the qualitative and quantitative determination of analyte in the test sample can be made. In order that the invention may be more fully understood, various embodiments will now be described by way of example only with reference to the accompanying drawings, wherein: FIG. 1 is an orthoganol view (from above and to the side) of one embodiment of device of the invention; FIG. 2 is a cross-sectional view taken generally along line 2-2 in Fig. 1; FIGS. 3,4 and 5 are cross-sectional views similar to Fig. 2, and showing stages in performing a test using the analytical device of Fig. 2; FIG. 6 is a cross-sectional elevational view of a sealed package containing the analytical device of Figs. 1 - 5; FIG. 7 is a top plan view of a second embodiment of an analytical device of the invention; FIGS. 8 and 9 are cross-sectional views taken generally along line 8-8 in Fig. 7 and showing stages in performing a test using the analytical device of Fig. 7; FIG. 10 is a top plan view of a third embodiment of analytical device of the invention; FIGS. 11 and 12 are cross-sectional views taken generally along line 11-11 in Fig. 10 showing stages in performing a test using the analytical device of Fig. 10; FIG. 13 is an enlarged sectional view through a portion of the device of Fig. 10; FIGS. 14A and 14B are top plan views of fourth and fifth embodiments of analytical devices of the invention; and FIG. 15 is a scatter plot of the correlation between assay results for the concentration of theophylline in a solution recorded in a test utilizing an analytical device constructed in accordance with the present invention, as compared with an assay pursuant to the Technicon Latex Turbidimitry method, as described in Example 1 hereafter. Referring now to Fig. 1 of the drawings, an analytical device 10 is shown which is configured and operable in accordance with one embodiment of the present invention for containing two substances or reagents initially in spaced relationship from one another, and thereafter to bring these substances into fluid contact either sequentially or concurrently in the presence of a liquid test sample to perform an assay. The present invention is applicable to analysis for the quantitative and qualitative determination of an analyte in a test sample wherein the sample to be tested is contacted with reagent(s) responsive to the presence and concentration of analyte in the sample to form a detectable response. By "detectable response", we mean a detectable change that is directly or indirectly indicative of the presence and/or concentration of the analyte. Unless otherwise indicated, all components of the analytical devices are preferably formed of a durable, resilient plastic material such as polyvinyl chloride (PVC), polystyrene, polyester, or cellulosic polymers and co-polymers, and the like. The plastic components may be thermoformed from sheet materials, although other manufacturing methods known in the plastic forming art may be used. With reference to Fig. 2, the analytical device 10 includes a base 12 of any suitable peripheral shape, including circular or polygonal, which is provided with a recess 14 therein for closely receiving a porous member 16. The upper surface 16a of the porous member may rest below the upper surface 12a of the base 12 when the porous member is positioned within the recess, to create a rim which serves to prevent overflow into the interior of the analytical device of liquid deposited on the porous member. It will be apparent that the recess 14 and porous member 16 may have a peripheral shape complementary with the base 12. Small projections or dimples, not shown, can be formed in the periphery of recess 14 to retain porous member 16 therein. The base 12 should be of sufficient thickness for it to provide support for the porous member 16. For example, and not by way of limitation, the base 12 may have a material thickness of about 0.020 inch (0.51mm). Porous member 16 can take many forms and be made of a variety of different materials including, for example, paper, woven and non-woven fabrics, porous ceramics, porous polyethylene and other foamed plastics. The material of porous member 16 may be of an open cell-type and, in a preferred arrangement, is an open cell reticulated foam having an interconnecting lattice structure. This material may have a three dimensional, interconnected cell structure that is about 95% void volume, and with approximately 50 cells per square inch (7.75 cells per cm²). This material has very suitable physical properties including a very large surface area to volume ratio, a large liquid hold-up volume, and it can be made hydrophilic. The lattice structure ensures uniform distribution of a solution throughout the volume of the porous member. In addition, the material is at least 90% transparent to visible light in thin sections of about one-eighth inch (3.2mm) thick. As described in the experiments hereinbelow, one suitable porous material is a polymer obtained from Porex Technologies of Fairburn, GA, having an average 35 to 50 micron (µm) pore size. The base 12 includes a cover member 18 which cooperates with the base 12. The cover member 18 is complementary to the shape of the base 12 and may be provided with a peripheral flange 20 which can be bonded, ultrasonically welded or otherwise suitably secured to the peripheral flange 22 of the base 12. To achieve the desired flexibility, the importance of which will be described, the cover member 18 is preferably formed from a relatively thin material, for example, a PVC sheet of 0.010 inch (0.25mm) thickness. For added flexibility, the cover member may be provided with a series of corrugations 24 to provide radial extension which is needed for displacement of the central portion 26 of the cover 18 towards the porous member 16. One possible use of an analytical device 10 is in automated clinical analyzers, and the base 12 and cover 18 may be contoured so as to permit stacking of individual devices within the loading magazine of such an instrument, as well as to permit ready removal of each device therefrom. The central region of the cover 18 is provided with a reaction well 28 and passage means 30 which are so constructed as to selectively release liquid contained in the reaction well 28 through the passage means 30 to the porous member 16 as will be described below. In accordance with one embodiment of the invention, the reaction well 28 is a central depression or funnel 32 in the central portion 26 of cover 18, defining storage means for a dry substance or reaction component 34. As noted above, passage means in the form of an opening 36 is provided in the reaction well 28 for selective transfer of a liquid within the reaction well into the porous member 16. In this embodiment, the opening 36 is sized such that surface tension between the liquid in the reaction well and the walls of the reaction well normally prevents movement of a liquid therethrough. For example, the opening may have a maximum diameter of 0.046 inch (1.17mm). The cover 18 may, for example, be made of a suitable plastic, which is normally hydrophobic. It is highly preferred, however, to use a plastic which is hydrophilic, i.e. the plastic should be appropriately formulated, or treated with surfactant after formulation, to make it hydrophilic, since hydrophilicity assists in ensuring uniform distribution of the liquid in the reaction well. In addition, the surface energy of the material from which the cover is formed should be such that, when compared to the surface tension of the liquid, the resulting net force will act to retain the liquid in the reaction well and prevent it from flowing through the opening. Note, however, that this force must not override the capillary attraction force created when the liquid comes into contact with the porous member 16 so as to have the undesired effect of hindering flow of the liquid into the porous member. An analyte responsive substance 38 which undergoes a detectable response to the presence and/or concentration of the analyte in the test sample, is dispersed throughout the porous member. It will be appreciated that the analyte responsive substance may be a mixture of two or more substances which together form a reagent component for the assay to be performed. Preferably, this analyte responsive substance 38 is dried within the voids in the lattice structure of porous member 16. For example, about thirty-five (35) microliters of a solution of the analyte responsive substance may be deposited on the porous member. Due to the substantial void volume within the porous member, the liquid analyte responsive substance readily disperses therethrough by capillary action due to the interconnecting lattice structure. The porous member may then be subjected to lyophilization to evaporate the liquid therefrom, resulting in a very thin film or coating of the dry analyte responsive substance being formed on the internal surfaces of the porous member. The thin film or coating is such that it occupies less than 10% of the void volume of the porous member. It should be noted that the liquid analyte responsive substance may be applied and evaporated from the porous member before or after it is placed in the recess of the base. A second substance or reaction component 34, which is intended to react with the test sample before the analyte comes into contact with the analyte responsive substance, may be provided on the cover 18. Thus, an aqueous solution of the substance can be deposited in the reaction well 28, but this will not flow through the opening 36 due to the surface tension between the liquid and walls of the reaction well discussed above. The liquid is thereafter evaporated, for example by lyophilization, to form a dry film or deposit in the reagent well. If desired, the analytical device 10 may be sealed within a package 38 as shown in Fig. 6 until the device is ready for use, to maintain the integrity of the reaction component and analyte responsive reagent. The package 38 can be in the form of metal or plastic foil sheets 40, 42 peripherally sealed together. The sequence of operation in performing an assay utilizing the analytical device 10 is illustrated in Figs. 3-5. An aliquot 44 of test sample (shown in phantom) is deposited in the reaction well 28 as shown in Fig. 3. The device of the present invention is suitable for analysis of relatively small volume test samples, e.g. 10 to 50 microliters. The drop of test sample may be discharged from a pipette tip 46 into which the sample has previously been aspirated as part of an analysis sequence performed by an automated clinical analyzer for example. It will be appreciated that such automated analysis systems are generally known in the art and do not form part of the present invention. In general, such automated analyzers are adapted to measure a characteristic of a sample fluid deposited on the analysis device and may include a device supply means, metering means for depositing a predetermined amount of sample on the device, incubator means, device transfer means for moving the analysis device from the incubator means, and a read station wherein the characteristic can be measured. Such analyzers are described, for example, in U.S. patent specification nos. 4,295,069, 4,296,070, 4,512,952 and 4,568,517 (Eastman Kodak Company). Alternatively, the aliquot 44 of the test sample may be manually pipetted onto the device. The liquid test sample 44 will mix with the dried reaction component 34 to reconstitute it and so form a combined liquid test sample and reaction mixture 48 (Fig. 4). The reaction mixture 48 so formed will flow, under the influence of gravity and capillary action, into the opening 36 to form a meniscus 50. The surface tension of the liquid reaction mixture 48 and the walls of the reaction well 28 and of the opening 36, will prevent the reaction mixture 48 from flowing through the opening 36 onto the porous member 16. After a suitable time interval sufficient to allow the desired specific interaction between the test sample 44 and the reaction component 34 to run substantially to completion, manual or mechanical pressure is then applied to cover 18, preferably within circumferential corrugation 24, to move the reaction well 28 to the transfer position shown in Fig. 5. This movement is possible because of the inherent flexibility of the cover 18 and the enhancement thereof by the corrugations 24. In this transfer position, the circumferential lip 52 of the opening 36 engages porous member 16 and the liquid meniscus 50 comes into contact with the porous member 16. The reaction mixture 48 will then flow through opening 36 into the hydrophilic, open structure of the porous member. The liquid reaction mixture 48 is thus absorbed by and dispersed within porous member 16, whereupon the analyte in the test sample will interact with the analyte responsive substance dispersed therein, with the resultant generation of a detectable response indicative of the presence and concentration of analyte in the test sample. The base 12 is preferably provided with an appropriate viewing port 54 through which the detectable response in the porous member 16 can be observed. Another embodiment of an analytical device of the invention is shown in Figs. 7,8 and 9. This is similar in many respects to that shown in Figs. 1-5 and like reference numerals designate like parts. In Figs. 7-9, the reaction well is an annular depression 56 in the cover 18, created by generally upright circular wall 58. A central dome-like projection 60 is connected to the wall 58 by a plurality of circumferentially spaced webs 62 having openings 64 therebetween. Preferably, the top of the dome-like projection 60 lies below the top surface of the cover 18 so that the devices may be stacked one on top of the other in a magazine or cassette, without the bottom of one device contacting the projection on the device upon which it rests. The openings 64 function in a like manner to opening 36, being sized such that surface tension between the liquid received or retained in the reagent well normally prevents the liquid from passing therethrough. The analytical device 10 of Figs. 7,8 and 9 is prepared and used in essentially the same manner as has been explained with reference to the device illustrated in Figs. 1-5. At least one dry analyte responsive substance 66 is contained within the porous member 16. A reaction component 68 is contained within the reaction well 28. To perform an assay, an aliquot of the test solution 44 is deposited within the reaction well 28, preferably directly over the dome-like projection 60 so that the same acts to disperse the test sample uniformly throughout the reaction well to reconstitute and mix with the reagent component 68 contained therein. The liquid reagent mixture so formed is retained in the reaction well and forms meniscus 70. Mechanical or manual pressure may be exerted on the central area 72 immediately surrounding the reagent well, to move webs 62 and openings 64 into engagement with porous member 16 as shown in Fig. 9. As in the embodiment discussed hereinabove, the thickness of the material forming the cover 18 is chosen to provide the necessary flexibility permitting such downward travel. Flexibility may also be provided at the shoulders 72a. The liquid meniscus 70 within each opening 62 thereby contacts porous member 16 so that the liquid reaction mixture within the reaction well flows into the porous member 16. As an alternative, pressure may be exerted directly on the dome-like projection 60, but this is not desirable in the case of automated clinical analyzers due to the possibility of reaction mixture carryover caused by the pressure applying mechanism coming into contact with successive reaction mixtures of successive analytical devices as downward force is applied to the projections. It will be appreciated that the downward travel of projection 60 is facilitated by the inherent flexibility of the material forming the cover 18 and the webs 62. Analytical devices of the present invention can be used in automated clinical analyzers. However, when they are so used, they are subjected to vibrational and other forces which can overcome the forces retaining the liquid in the reaction wells. Accordingly, in another embodiment of the present invention, means are provided to reduce the disadvantageous effects of such vibrational and other forces. One such embodiment is shown by way of example in Figs. 10 to 13. As will be readily understood, these figures are similar in many respects to the embodiment shown in Figs. 7-9, and like reference numerals designate like parts throughout. In the embodiment of Figs. 10 to 13, the reaction well is provided with a transverse wall which effectively serves as a bottom, and the side walls are configured to reduce unwanted reaction mixture spillage due to system vibration, translational or other forces acting on the device. With reference to Figs. 11 and 13, the wall 58 of the reaction well 28 has a slightly downwardly divergent configuration, i.e. the diameter of the reaction well 28 increases with depth (as is shown exaggerated in Fig. 13). A transverse wall 74, which may be of generally concave cross-sectional configuration as shown, is connected to the annular wall 58. Centrally disposed in the reaction well is a frusto-conical projection 76. The top of the frusto-conical projection 76, as with the dome-like projection 60, lies beneath the top surface of the cover 18. Likewise, when a drop of a test sample is deposited on the frusto-conical projection 76, the latter acts to disperse the test sample uniformly throughout the reaction well. The transverse wall 74 is provided with one or more arcuate slits 78 which are normally effectively closed. Preferably, in order to provide suitable flexibility, the slits extend into the reaction well wall as shown in Fig. 13. When the central area 72 of the cover member 18 is depressed (Fig. 12), the transverse wall 74, due in part to its concave cross-sectional configuration, is sufficiently deformed so that the slits 78 open, permitting the reaction mixture to flow through the slits 78 and to contact and be absorbed by the porous member 18. Figs. 14a and 14b show two modifications which may be used in place of the arcuate slits 78 shown in Fig. 10. Thus, a multiplicity of holes 80 (Fig. 14a) or radial slits 82 (Fig. 14b) may be provided in the transverse wall 74. The analytical devices of the invention are adapted to contain two substances or reagents initially in spaced relationship from one another, and thereafter to bring these substances into fluid contact in the presence of a liquid test sample to perform an assay. The devices are so constructed as to permit a wide variety of assays to be performed, by varying the reaction components and analyte responsive substances used. For example, a sample can be pretreated by exposure to a reaction component for a certain time before it is exposed to further reagents. In such instances, the reaction component can include a substance which physically changes the sample, such as a cytolytic agent, to release an analyte for detection. For example, where the analyte is hemoglobin, the substance can be a cytoloytic agent such as a surfactant. The surfactant can, for example, include polyoxyethylene ethers of aliphatic alcohols such as Brij surfactants (ICI United States Wilmington, DE), polyoxyethylene derivatives of sorbitol anhydride fatty acid partial esters such as Tween surfactants (ICI United States, supra ) and alkylaryl polyethers of alcohols, sulfonates, or sulfates such as Triton surfactants (Rohm & Haas Company, Philadelphia, PA). ("Brij", "Tween" and "Triton" are trademarks.) Thus, a surfactant may for example be placed in the reaction well 28 and a hemoglobin reactive substance in the porous member 16. Similarly, the chylomicrons in serum samples can be broken up first by the action of a surfactant in the reaction well before triglyceride is reacted with triglyceride responsive substances in the porous member 16. Clinical diagnostic tests frequently involve several reactive components such as the reaction component itself and the analyte responsive component. The reaction component may be responsive to the analyte to form a reaction product and the analyte responsive substance then effects a detectable response to the reaction product. The reaction component may contain expensive enzymes labile biological substances which are susceptible to denaturing or degradation by the analyte responsive substance due to incompatible pH, ionic strength or chemistry if kept together. Therefore, the reaction component can be made more stable by means of physical segregation from the analyte responsive substance. The analytical devices of the invention can provide such segregation or compartmentalization of reaction components. The reaction component (R₁) may be stored in the reaction well 28, and the analyte responsive substance (R₂) in the porous member 16. Where the analyte is glucose, the test sample may first be reacted with glucose oxidase in the reaction well on the cover. The hydrogen peroxide produced can then react with peroxidase together with a redox indicator to produce a detectable colorimetric response in the porous member. Similarly, where the analyte is cholesterol, the test sample may first be reacted with cholesterol esterase and cholesterol oxidase in the reaction well before the peroxidase reaction is initiated in the porous member. When an interfering species is present in the test sample, it may be removed first by using a suitable agent in, for example, the reaction well. Thus, the agent can be a chemical substance that reacts specifically with the interfering species only. For example, as demonstrated in Example 2 below, in the case of ascorbic acid interference in clinical serum samples, ascorbate oxidase may be placed in the reaction well to destroy the ascorbic acid before the analyte is reacted to give a detectable response in the porous member. In the case of protein interference in total bilirubin analysis, diphylline or caffeine can be placed in the reaction well to first displace bilirubin from protein binding in the serum sample before it is reacted with diazosulfanilic acid in the porous member. Alternatively, the reaction component and analyte responsive substance may comprise reagents for a homogeneous specific binding assay system which produces a detectable response that is a function of the presence of the analyte in the sample. Such homogeneous specific binding assay systems can include a label which participates in an enzymatic reaction. More particularly, one preferred format of the homogeneous specific binding assay reagent and system include an antibody which binds the analyte, a conjugate of the analyte or a binding analog thereof and a label, and a detection system which interacts with the label to produce a detectable response which response, when the label conjugate is bound by an antibody, is different from that when it is not so bound. Any of the various label systems which are known to be suitable for use in homogeneous immunoassays can be used in the present device and method. In another application of the present invention, substances are used in the reaction well to filter out or absorb undesirable material in the test sample. For example, the reaction well can be packed with activated charcoal or another absorbent to selectively remove interfering substances. Alternatively, it can be packed with fiberglass or other filtering aids which can hold back blood cells from whole blood samples, or cell debris and salt crystals from urine samples, for example. In this case, the passage or opening 36 in the well must be sized to retain the filtering material but to allow the interference-free test sample to pass through when the reaction well is manipulated to cause the reaction mixture to contact the porous element. The reagent systems which can be used provide, or can be readily adapted to provide, a detectable response, such as a color change, related to the presence, or the amount (or both) of the analyte under assay in the liquid sample. The porous element can provide enhanced electro-magnetic radiation signals such as a change in light reflectance in the visible spectrum, thereby producing a visible color change, or a change in light reflectance outside the visible range such as in the ultraviolet range or infrared range. The detectable response is preferably one which can be observed through the senses directly or by use of ancillary detection means, such as a spectrophotometer or other sensing means. When the analytical result is obtained as a detectable change, it can be measured such as by passing the analytical device through a field in which suitable apparatus for reflectance measurement is provided. Such apparatus serves to direct into the element a beam of energy, such as light, which is then reflected from the element back to a detector. Generally, electro-magnetic radiation in the range of from about 200 to about 900nm has been found useful for such measurements. By measuring the detectable response produced by the analyte responsive substance and comparing the detectable response so produced with the detectable response produced when the analysis is conducted with a series of standard compositions containing known amounts of analyte, the qualitative and quantitative determination of analyte in the test sample can be made. In order that the invention may be more fully understood, the following Examples are given by way of illustration only. Example 1 This Example illustrates use of an analytical device of Figs. 1-5 for determining the presence of theophylline in serum. The devices used were as in Figs. 1 to 5, and were made of components thermoformed from PVC sheet material. In each device, the base 12 had a thickness of 0.020 inch (0.51mm); the cover 18 a thickness of 0.010 inch (0.25mm), and the porous member, obtained from Porex Technologies of Fairburn, GA, had a thickness of one thirty second (1/32) of an inch (0.80mm) and an average pore size of 35µm (microns). Two reagents, R₁ and R₂, were formulated. R₁ corresponded to the reaction component 34; R₂ corresponded to the analyte responsive substance 38. R₁ contained the following: 0.05 M imidazole - HCl buffer pH 7.5, 0.6 mM magnesium acetate, 0.2 mM EDTA, 0.5 mg/ml IgG, 0.49 IU/ml diaphorase, 4 IU/ml glucose-6-phosphate dehydrogenase, 2.4 IU/ml phosphoglucomutase, 104 IU/ℓ phosphoacetyl glucomutase, 10 µl/ml purified monoclonal antibody to theophylline (Beckman Lot No. 706022), 1% Dextran T₇₀ and 5% mannitol. The Commission of Enzymes of the International Union of Biochemistry has defined an International Unit (IU) of enzyme activity as 1 micromole (µmol) of substrate utilized per minute under specified conditions of pH and temperature. R₂ contained the following: 1mM glucose-1-phosphate, 2mM NAD, 0.5 mM p-iodonitrotetrazolium violet, 0.23 µM theophylline glucosamine diphosphate conjugate and 4% hydroxypropyl methyl cellulose. Into the reagent well 24 and porous member 16, respectively, of each device were placed thirty-five microliters of each of R₁ and R₂ respectively. The reagent impregnated devices were then lyophilized, and finally sealed in individual foil pouches and kept under refrigeration. Pooled serum samples were used to prepare theophylline standards. Thirty-five microliters of the serum standard diluted 1:100 were pipetted onto the reaction well 28, and the lyophilized R₁ was allowed to dissolve completely to form a reaction mixture in a period of three minutes. By means of a plunger, the reagent well was then manually brought into contact with the porous member 18 for five seconds, during which time all the reaction mixture transferred to the porous member 16 by capillary action. The diffused reflectance optical density at 500 nm was monitored off the underside of the porous member 16 over a period of five minutes. The change in optical density between the one and three minute interval was plotted against the concentration of theophylline to provide a standard curve. Thirty-one clinical serum samples containing various levels of theophylline were used as unknowns and their values were computed from the standard curve. The results were compared to those obtained pursuant to a commercial latex turbidity method run on the TECHNICON RA-1000 clinical analysis system (TECHNICON RA-1000 is a registered trademark of Technicon Instruments Corporation, Tarrytown, NY). The correlation coefficient was 0.944, the slope was 1.011 and the intercept was -2.264 (see Fig. 15). The results obtained utilizing the analytical device thus compared favourably with those of a commercial latex method. EXAMPLE 2 This Example demonstrates the use of a device of Figs. 10-13 to eliminate ascorbic acid interference from uric acid analysis in a sequential reaction scheme. It is known that ascorbic acid can occur in serum in high concentrations which can cause significant error in clinical tests. The analytical devices comprised components thermoformed from high impact polystyrene sheet material. The base 12 had a thickness of 0.060 inches (1.5mm); the cover 18 a thickness of 0.010 inches (0.25mm), and the porous member 16, obtained from Porex Technologies of Fairburn, GA, a thickness of one thirty second (1/32) of an inch (0.80mm) and an average pore size of 50 µm (microns). Two reagents, R₁ and R₂ were formulated. R₁ was placed in the reaction well 28 and R₂ on the hydrophilic porous member 16. R₁ contained an agent which was able to destroy the interference when the test sample was placed in contact with it. In this example, ascorbate oxidase was used to react with ascorbic acid in the test sample to remove the ascorbic acid. R₁ contained the following: 100,000 IU/ℓ ascorbate oxidase, 2.5 g/ℓ bovine serum albumin, and 50 g/ℓ mannitol. R₂ contained the following: 375,000 IU/ℓ horse radish peroxidase, 40,000 IU/ℓ uricase, 25g/ℓ bovine serum albumin, 50 g/ℓ 4-amino antipyrene, 75g/ℓ sodium p-hydroxybenzoate, 10 g/ℓ hydroxypropyl methyl cellulose, 20mM sodium azide, 1mM EDTA, and 0.2M phosphate buffer, pH 8.5. Twenty microliters of each reagent were deposited onto the devices. The reagent impregnated devices were then lyophilized and kept in a desiccator. Aqueous standards containing 0, 5 , 10, 15 and 20 mg/dl uric acid were prepared and used to establish a standard curve. An analytical sample containing 10 mg/dl uric acid plus 10mg/dl ascorbic acid was also prepared. Tests were performed to compare the efficiency of (i) the analytical device 10 in which ascorbate oxidase was contained in R₁ and reacted first with the sample reaction mixture then exposed to R₂ (Device 1 hereinbelow) to (ii) a device in which the cover 18 was removed, and the ascorbate oxidase reacted concurrently with R₂ on the sample (Device 2). Measurements were performed using twenty microliters of standard or sample. For Device 1, the analytical sample was introduced to the reaction well 28 and allowed to incubate with the ascorbate oxidase. Then the reaction well 28 was brought into contact with the porous member 16 by means of a plunger. A five second contact time was sufficient to transfer all the fluid from the reaction well to the hydrophilic porous member 16. For Device 2, the test solutions were placed directly in the hydrophilic porous member impregnated with R₂. The diffused reflectance optical density at 540nm was monitored off the underside of the porous member over a period of five minutes at 37°C on an InfraAnalyzer 300 reflectance spectrometer (Technicon Instruments Corporation, Tarrytown, NY), which was modified to cover the spectral range between 340 and 700 nm. The optical density at the end of five minutes was recorded. The recovered values of uric acid in the test sample containing 10 mg/dl ascorbic acid interferent were computed from the standard curve. The result is summarized in Table 1. A 100% recovery of the uric acid value was obtained with ascorbate oxidase in R₁ on the analytical device whereas use of ascorbate oxidase in R₂ alone recovered only 67% of the uric acid value. This clearly demonstrates that the device of this invention is very effective in removing interference in analytical samples or providing a sequential reaction mechanism. Recovered uric acid values in sample containing 10 mg/dl ascorbic acid Theoretical Value No Ascorbate Oxidase Device 2 Ascorbate Oxidase in R₂ Device 1 Ascorbate Oxidase in R₁ 10.0 mg/dl 0.3 mg/dl 6.7 mg/dl 10.0 mg/dl It will be evident from the foregoing description that the invention includes an analytical test device which maintains two substances or reagents initially in spaced relationship from one another, and thereafter is adapted to bring these substances into fluid contact either sequentially or concurrently with each other in the presence of a liquid test sample to perform an assay. Both substances may be present in a dry form, and reconstituted by the liquid test sample.

Claims: An analytical device (10) for the qualitative and/or quantitative determination of an analyte in a liquid test sample, said analytical device comprising: a) a base (12); b) a porous member (16) received in said base; c) at least one analyte responsive substance (38;66) dispersed throughout said porous member which substance undergoes a detectable response to the presence and/or concentration of said analyte; d) a reaction component (34;68); e) a cover (18) integral with said base; f) a reaction well (28;56) in said cover (18) for storing said reaction component and for receiving said liquid test sample whereby said liquid test sample and said reaction component can form a liquid reaction mixture within said reaction well; g) passage means (30;80;82) in said reaction well for transferring said reaction mixture therethrough, said passage means being spaced from said porous member (16) and effectively closed to transfer therethrough of said reaction mixture, said passage means being selectively movable toward said porous member effectively to open the passage to allow said reaction mixture to flow therethrough to said porous member, whereby said analyte responsive substance in said porous member can undergo a detectable response to said analyte present in said liquid reaction mixture; and h) said base includes an observation port to expose said porous member to observation for any detectable response of said analyte responsive substance thereon. A device according to claim 1, wherein said passage means (30) is normally open and is sized such that surface tension of said liquid reaction mixture with said reaction well (28) prevents said liquid reaction mixture held in said reaction well from transfer through said passage means. A device according to claim 1 or 2, wherein said liquid reaction mixture held by said reaction well (28;56) is drawn through said passage means (30,80,82) by capillary attraction when said passage means is moved into engagement with said porous member (16). A device according to claim 1,2 or 3, wherein said reaction well (28) is a conical depression (32) in said cover (18). A device according to claim 4, wherein said cover (18) includes a central portion (26), said reaction well (28) is positioned within said central portion, and deflective means are provided integral with said central portion for displacement of said central portion towards said porous member (16). A device according to claim 1,2 or 3, wherein said reaction well is a generally annular depression (56) in said cover (18) with a projection (60) centrally positioned within said depression (56) and at least two support arms (62) extending from said projection to the side of the reaction well defining openings (64) therebetween constituting said passage means. A device according to any of claims 1 to 6, wherein said reaction component (34;68) is a dry substance within said reaction well (28;56) and can be reconstituted upon contact with said liquid test sample. A device according to any of claims 1 to 7, including at least one deformable circumferential corrugation (24) in said cover (18) to facilitate movement of passage means to the transfer position. A method of qualitative and/or quantitative determination of an analyte in a liquid test sample, said method comprising the steps of: a) depositing an aliquot of said liquid test sample in the reaction well of an analytical device as claimed in any of claims 1 to 8; b) permitting said aliquot of liquid test sample and said reaction component to form a liquid reaction mixture within said well; c) displacing said passage means toward said porous member to effectively open the passage and allow the reaction mixture to flow therethrough to said porous member, whereby said analyte responsive substance will undergo a detectable response to any said analyte present in said liquid reaction mixture; d) detecting and/or measuring the detectable response produced by said analyte responsive substance; and optionally e) comparing the detectable response produced by said test sample with the detectable response produced by a series of standard compositions containing known amounts of said analyte.

Inventors: ADLER, STANFORD L., CAMPISI, JOHN, LEONG, KOON-WAH
Applicants: MILES INC.(AN INDIANA CORP.)
Application year: 1989
Main classification: G01N33
IPC codes: G01N33, G01N21, G01N31