EP0575597A1 - Multi-test immunochemical reagent and method to use same - Google Patents

Abstract

The invention relates to an immunochemical reagent for multiple assays, and to a method of using this reagent in radial sharing immunoassays. More particularly, the invention relates to a human immunochemical reagent comprising an antiserum directed against a specific animal species, adsorbed on a porous and inert support.

Description

MULTI-TEST IMMUNOCHEMICAL REAGENT AND METHOD TO USE SAME CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co- pending application, Serial Number 07/294,931 filed January 3, 1989, which is a continuation of U.S. Serial No. 693,569 filed January 22, 1985, which is in turn a continuation-in-part of U.S. Serial No. 227,664 entitled "Solid Phase system for Ligand Assay" filed on January 23, 1981, now U.S. Patent No. 4,517,288. BACKGROUND OF THE INVENTION

Field of the Invention: This invention is directed to a method and a composition of matter. More specifically, this invention concerns itself with a multi-test solid phase or support (i.e., a porous medium) used to conduct a variety of immunoassays. Description of the Prior Art: The various techniques which have been previously described in the technical and patent literature relating to immunoassay, in general, involve four basic processes for the isolation/detection of a reaction product (generally containing the analyte of interest) . A common form of immunoassay involves the immunochemical interaction of an analyte of interest with a ligand (antigen or antibody) thereby resulting in the formation of an immunoprecipitate; the presence of the precipitate being indicative of the presence of the analyte.

Where the immunocomplex remains in solution, it can be readily precipitated by addition of a second antibody

(i.e. double antibody precipitation). The more sophisticated of these immunoassays

(semi-quantitative and quantitative) are generally referred to as a homogeneous immunoassay; and, the solid phase immunoassays, which include the classical heterogenous systems (i.e. U.S. Patent No. 3,654,090), the multiple zone solid phase systems (i.e. U.S. Patent No. 4,258,001) and the solid phase radial partition immunoassay system (i.e. U.S. Patent No. 4,517,208) . In the homogeneous immunoassay systems of the type currently in use, the entire assay is conducted within a single, essentially fluid phase. The reactants, sample and indicator are contained within the same liquid fraction and the monitoring of the amount of indicator is performed without any separation between the immunochemically bound materials and those which remain free in the fluid.

In the classical heterogeneous immunoassays described in the technical and patent literature, one component of the immunochemical -reaction is often immobilized on a solid phase or support. The need for such immobilization is the requirement, in such system, to separate the immunochemically bound constituents (presumably bound to the solid phase) from the unbound constituents. The demands of this system traditionally require that the bound materials (solid phase) and the unbound materials (liquid phase) be separated into two (2) mutually exclusive fractions. The immobilization of one of the immunochemical reactants on the solid phase in this system provides the most practical means for achieving such separation.

The multiple zone solid phase system described in the above referenced patent involves immunochemical interactions which are similar to the classical heterogenous assay described previously; however, the separation of the immobilized constituents from the more mobile constituents is effected by transfer or elution thereof from one contiguous zone (i.e. contiguous laminae) to another.

The fourth immunoassay system, which has most recently evolved, is a hybrid of both classical heterogeneous and the homogeneous immunoassay systems and yet distinctive from the multiple zone system discussed hereinabove. This hybrid, more descriptively characterized as "solid phase, radial partition immunoassay", initially involves the immobilization, within a solid phase, of an im unoreagent (i.e., an antibody). Subsequent thereto, an aliquot of patient's sample is applied to the portion of the solid phase containing the immobilized immunoreagent. After a brief incubation period, a second immunoreagent (generally a ligand conjugated to an indicator) is applied to the solid phase in a similar fashion, and allowed to interact with either the immunoreagent, which has been immobilized within the solid phase, or with the analyte from the patient's sample, depending upon the nature of the analytical protocol (i.e., competitive or sandwich assay) . The manner in which the various materials are applied to the solid phase containing the immobilized immunoreagent defines the reaction zone within the solid phase. Subsequent to such interactions, a wash solution may be dispensed onto this reaction zone, whereby unbound materials (i.e., materials which have not immunochemically reacted directly or indirectly with the immobilized reagent) are eluted from the reaction zone in a radial pattern, thereby producing an area within the reaction zone which is essentially free of unbound materials. The ability of this type of assay to achieve such redistribution of materials entirely within the single solid phase is unique and effectively excludes, from that portion of the reaction zone, materials which could interfere in the monitoring and determination of the amount of analyte.

As is evident from the above discussion of the classical heterogeneous immunoassay system, and more recently developed solid phase radial partition immunoassay, both such systems are dependent, for their success, upon a clean separation between bound and unbound materials. In the context of a radial partition immunoassay, such separation occurs entirely within a single, solid phase, whereas, in classical heterogeneous systems, the solid phase and liquid phases are separated into two mutually exclusive fractions. In such solid phase systems, it is both desirable, and in certain instances essential, that the solid phase to which the immobilized immunoreagent is adsorbed, be essentially inert. This requirement is recognized in the art as essential to the avoidance of nonspecific binding of proteins and other materials, (which are endogenous to the biological sample being analyzed) , so as to thereby prevent interference or distortion of the binding selectivity of the immunochemical reaction.

The various mechanisms by which an immunoreagent can be immobilized upon the surface of a solid phase can involve any one or a combination of mechanisms, including adsorption, absorption or covalent bonding, see U.S. Patent No. 4,168,146 (to Grubb) . Grubb uses a variety of reagents, including cyanogen bromide and glutaraldehyde to covalently bond antibody to a variety of different substrates (i.e. cellulose containing materials, cellulose acetate film or a microporous plastic sheet containing silica) . Unfortunately, many of these same substrates are relatively immunochemically reactive and tend to indiscriminately adsorb proteins from the sample. Where one attempts to use a relatively inert substrate such as glass, the amount of adsorption of, for example, antibody or other im unoreagents, is generally unsatisfactory for use in a solid phase immunoassay, see U.S. Patent No. 3,790,663 (to Garrison) for discussion of inadequacies of glass substrates.

Because of the desirability of an inert substrate as a matrix for immunochemistry, efforts have continued to adapt such inert material for immunoassay procedures. One such attempt involved the co- precipitation of antibodies within a glass fiber matrix, see U.S. Patent No. 3,888,629 (to Bagshawe) . In addressing this problem of nonspecific adsorption of proteinaceous material, Bagshawe attempted to pretreat his solid phase or matrix with a macro molecular substance such as albumin to prevent the non-specific binding of immunogens to the matrix. In an alternative embodiment of his invention, Bagshawe also described a procedure for the sensitization of his matrix with an immunoreagent by formation of an immunoprecipitate within the interstices of the matrix. Thus, the particles of the immunoprecipitate were physically entrapped within the matrix. Accordingly, Bagshawe perceived his invention as overcoming some of the disadvantages of the prior art systems in that he was now able to use a relatively inert matrix (glass being listed among the suitable medium, column 1, line 41) without being dependent upon the adsorption characteristics of the inert matrix for retention of his immunoreagent.

As is readily appreciated, comparison of the amount of binding activity per unit of immunoreagent in an immunoprecipitate is significantly less than the activity per unit of immunoreagent where the same immunoreagent is adsorbed onto a solid phase. Thus, while Bagshawe's approach to the problems associated with the sensitization of inert materials appeared to be effective, it was highly inefficient from a reagent utilization standpoint and was at best a make-shift solution to a long standing problem. As is further evident, the preferred form of association of the immunoreagent with a matrix (of the type used by Bagshaye) would be to have such materials adsorbed onto the surface of the matrix so as to take full advantage of its high surface area characteristics. Thus, Bagshawe's use of an immunoprecipitate in conjunction with the solid phase is, at best, a compromise and falls short of making most effective use of either the immunoreagent and/or the inert matrix.

Thus, a continuing need exists for a method for the adsorption of immunoreagents on to the surface of inert solid phase support or medium. Ideally such method should be consistent with the utilization of the high surface area characteristics of this type of support, and yet minimizes consumption of immunoreagent. The above and related objects were achieved by providing an improved method for adsorption of an immunoreagent on to an essentially inert porous medium comprising applying to said porous medium, under adsorption conditions, an essentially soluble immunocomplex of an immunoreagent and an antiserum to said immunoreagent. U.S. Patent No. 4,517,288. The amount of soluble immunocomplex adsorbed on to the porous medium was based upon what was empirically determined to be effective to selectively bind and retain an analyte of interest to the immunoreagent within a defined area of the porous medium in the context of a particular immunoassay. Accordingly, the prescription of an effective amount can vary from immunoassay to immunoassay, and be further dependent upon the physical geometry of the solid phase and the manner in which the assay results are monitored. A shortcoming of this method, however, is that different soluble immunocomplexes adsorbed on to the porous medium are needed for each different type of immunoassay; as such a need exists to develop a multi- test immunoreactant that can be used in a variety of immunoassays. Summary of the Invention Accordingly, it is an object of this invention to remedy the above discussed deficiencies. In particular, this invention provides an immunochemical reagent made of secondary antibodies absorbed on to an inert porous medium. More specifically, this invention provides an immunochemical reagent made of anti-serum to a specific species adsorbed on to an inert porous medium. The anti-serum may be for example, goat anti-mouse, goat anti-rabbit, goat anti- sheep, sheep anti-goat, rabbit anti-goat, donkey anti- goat or more generally, a second species anti first species. For purposes of this invention, anti-sera may be referred to herein as secondary antibody. The secondary antibody may be purified or unpurified. Additionally, combinations of the various specific animal species may also be applied to a solid phase. These immunoreagents adsorbed on to the surface of an inert solid phase or support can be used for numerous immunoassays.

In particular this invention provides a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the method involving: a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the solid phase consisting essentially of secondary antibodies immobilized on a solid support, the method involving: combining under binding conditions, a fluid sample containing the analyte and the primary antibodies to form a fluid mixture of analyte-primary antibody complexes and primary uncomplexed antibodies; applying the fluid mixture under binding conditions to the solid support to bind analyte-primary antibody complexes and uncomplexed primary antibody; applying an indicator to the solid phase under binding conditions to bind with bound uncomplexed antibody or to bind with bound analyte; observing the extent to which the indicator is present on the solid support; and correlating the extent to which the indicator is present of the solid support with the amount of unknown analyte in the sample. The indicator may also be added to the fluid sample; this can be done by either adding the components at the same time or allowing the analyte and antibody to briefly incubate before the addition of the indicator. Binding conditions are further delineated in P. Tijssen, Laboratory Techniques in Biochemistry. Molecular Biology, Practice and Theory of Enzyme Immunoassay 123-145. (4th ed. 1987) (hereby incorporated by reference) .

The term indicator in the context of this invention means a labeled conjugate. The conjugate is antibody or an analyte depending on the assay format. The label is a fluorescent, enzymatic, colorometric or radio etric compound that is associated either directly or indirectly with the conjugate. The label may be comprised of an enzymatic compound that produces fluorescence upon contact with a substrate. The extent to which the indicator is present on the solid support can be correlated with the amount of unknown analyte. P. Tijssen, Laboratory Techniques in Biochemistry. Molecular Biology, Practice and Theory of Enzyme Immunoassay 173-217 and 368-376. (4th ed. 1987) (hereby incorporated by reference) .

This invention also provides a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the solid phase consisting essentially of secondary antibodies immobilized within a finite zone of the interstices of a solid, inert, porous support, the method involving: combining under binding conditions a fluid sample containing the analyte and primary antibodies to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; applying the fluid mixture under binding conditions to the center of the finite zone to bind analyte-primary antibody complexes and uncomplexed antibody; applying an indicator to the solid support under binding conditions to bind with uncomplexed antibody; observing the extent to which the indicator is present within a delimited area of the reaction zone; and correlating the extent to which the indicator is present in the delimited area with the amount of unknown analyte in the sample. Additionally, this invention provides a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the method involving: a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the solid phase consisting essentially of secondary antibodies immobilized on a solid support, the method involving: applying under binding conditions primary antibody to the solid support; applying under binding conditions the fluid sample to the solid support; applying an indicator to the solid phase under binding conditions to bind with bound uncomplexed antibody; observing the extent to which the indicator is present on the solid support; and correlating the extent to which the indicator is present of the solid support with the amount of unknown analyte in the sample.

This invention also provides a method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, the solid phase consisting essentially of secondary antibodies immobilized within a inite zone of the interstices of a solid, inert, porous support, the method involving: applying under binding conditions primary antibody to the center of the finite zone of the solid support; applying an indicator to the solid support under binding conditions to bind with uncomplexed antibodies, applying under binding conditions the fluid sample to the center of the finite zone of the solid support; observing the extent to which the indicator is present within a delimited area of the reaction zone; and correlating the extent to which the indicator is present in the delimited area with the amount of unknown analyte in the sample. Brief Description of the Drawings Fig.l shows response of a calibrator versus percent (%) goat anti-mouse immunoglobulin adsorbed on an inert porous matrix. Fig.2 shows response versus percent (%) goat anti- rabbit in normal rabbit serum. Fig.3 shows titration of rabbit anti-ββtradiol

Pig.4 ^' shows comparison of STRATUS* (Baxter Diagnostics Inc.) eβtradiol versus multi- test calibration-curves. Fig.5 shows a comparison of response versus concentration of estradiol in terms of STRATUS^ (Baxter Diagnostics Inc.) performance versus the multi-test method. Description of the Invention Including Preferred Embodiments

The multi-test immunoreagents contemplated by this invention are porous inert medium having adsorbed thereto species specific antiserum or antiserum from a homologous species. These reagents do not contain specific antibody and are capable of binding any primary antibody. In particular, goat anti-rabbit and goat anti-mouse antiserum function well as the antiserum adsorbed to the porous inert medium. Antisera is prepared by injecting the immunoglobulin from a first species into a second species. The second species develops antiserum against the immunoglobulin of the first species, or more generally a second species anti first species. For purposes of this invention anti-sera may be referred to herein as secondary antibody. The secondary antibody may be purified or unpurified.

A primary antibody is an antibody which is specific for an analyte, for example anti-hCG antibody is specific for hCG. Primary antibodies may be developed from a variety of species using standard techniques, however, the species most commonly used are rabbits and mice. Any primary antibody developed in a species will be recognized by antiserum against that species. For example, a primary antibody developed in a mouse will be recognized by antisera such as goat anti-mouse or rabbit anti-mouse. Since rabbits and mice are the most common species used to develop primary antibodies and most common antisera is second species anti-mouse or anti-rabbit.

Because of the homology between certain strains of primary antibody, a secondary antibody developed against a species may also react with other closely related species. For example, goat anti-mouse will often react with primary antibody prepared from a rat. For purposes of this invention these species are referred to herein as homologous species.

Primary antibody as used herein means an antibody specific for an analyte that immunologically reacts with the appropriate antisera and includes primary antibody from the specific species and any homologous species. The benefit of this is that it provides a wider selection of antibodies. The solid phase which is compatible with the foregoing objectives of this invention may be "inert". More specifically, the characterization of a solid phase as "inert" (in the context of this invention) is intended as referring to the relative nonreactive character of the surface of the solid phase with respect to its ability to indiscriminately adsorb proteinaceous materials. As noted earlier herein, in the Background section of this disclosure, glass and other materials similar in chemical composition, are generally regarded as relatively inert in comparison to other more reactive materials when measured against their ability to adsorb protein.

In the preferred embodiments of this invention, the physical form of the solid phase is such that the inter-stices or pores within such solid phase are sufficiently small so that the reaction fluids are retained and transported therebetween by capillary action. The solid phase is advantageously composed of a mat of compressed fibers, such as glass or synthetic fibers. This solid phase may also be constructed of other porous constituents such as sintered glass, ceramics and synthetic polymeric materials. Glass fiber filter paper is the preferred solid support of this invention because of its inert characteristics and because of its ability to adsorb the soluble immunocomplex of this invention in quantities sufficient for the sensitization of the glass fibers so as to render it suitable in immunoassay.

The multi-test immunochemical reagent can be used in a wide variety of analytical protocols for analysis of a variety of biological and industrial fluids. It should be noted that a single glass fiber filter paper can be. used for any assay and may contain antiserum for a number of species. For instance, these reagents can be advantageously used for the immunoassay of blood or urine in the rapid and quantitative analysis of such fluid for the presence of therapeutic drugs, natural or synthetic steroids, hormones, antibodies and other analytes of interest.

Exemplary of therapeutic drugs which can be analyzed in such a protocol include digoxin, dilantin, phenobarbital, theophylline, gentamicin, quinidine, and the like. Multi-test immunochemical reagent prepared in the foregoing manner can also be utilized in the immunoassay for the detection of steroids, such as cortisol, aldosterone, testosterone, progesterone, and estriol or serum protein, such as ferritin.

Hormone levels are also capable of determination through the use of appropriate immunochemical reagents, immobilized as described hereinabove, on an appropriate solid phase. These hormones include the thyroid hormones, i.e. triiodo-thyronine or thyroid stimulating hormone (TSH) ; the peptide hormones, i.e. insulin, corticotropin, gastrin, angiotensin, and proangiotensin; the polypeptide hormones, i.e. thyrotropin, levteotropin, and somatotropin human chorionic gonadotropic hormone (HCG) .

The assay format includes both competitive and sandwich assays. In the competitive assay the conjugate may be added simultaneously with the sample containing the analyte and the specific antibody.

EXAMPLE 1 - Goat-anti-mouse Multi-test Immunochemical

Reagent Used in an Assay for Estradiol

Below is a description of the multi-test immunochemical materials and selection means for determining optimum concentrations of goat anti-mouse antibody and a rat anti-estradiol antibody to be used in an assay for estradiol. Materials

Estradiol conjugate: an estradiol conjugate of .estradiol (E2) and alkaline phosphatase (ALP) were prepared using a standard mixed anhydride method. (B.K. Van Weeman, FEBS LETTERS Vol.24, No.l, July 1972) . The resulting E2-ALP conjugate was diluted to .04 μg/mL in 50 mM Tris, pH 8.0, 50 M NaCl containing 0.1% protein with 0.1% azide added as a preservative. Estradiol Calibrators: An estradiol stock solution of 100 μg/mL of estradiol in 80% ethanol was prepared. Aliquots of the Estradiol stock were added to charcoal stripped human serum to produce a set of estradiol calibrators at 0(A), 20(B), 50(C), 200(D), 500(E), 2000(F) pg/mL. Calibrators are a standard that has a specific amount of analyte.

Substrate/Wash: A solution containing 1 mM 4- methylumbelliferyl phosphate in diethanolamine buffer, pH 9.0, containing stabilizers, surfactant and blue dye, with 0.1% sodium azide added as a preservative. Rat anti-estradiol monoclonal antibody (Rat anti- F2) was obtained from OEM Concepts, Inc.

Goat anti-mouse monoclonal antibody (GAM) was prepared using conventional procedures. Preparation and Optimization of Goat Anti-Mouse Multi- Test Reagent

Solutions of zero to eight percent goat anti- mouse (GAM), at .5% increments, diluted in a 50 mM Tris buffer, pH 8.0, containing 0.5% ZONLY FSN (a surfactant manufactured by DuPont) were prepared. The solutions were then filtered with a .8μm filter to remove particulates. Multiple tabs of glass fiber filter paper (Whatman GF/F) were spotted to within 76 μL of each solution and dried to immobilize the antibodies on to the tab.

The tabs spotted with the incremental solutions of GAM were evaluated as follows: One hundred microliters of a 1/100 dilution of Rat anti-E2 were added to 100 μL of 0(A) calibrator. One hundred and fifty microliter aliquots of the mixture were added to the tabs in the zone containing the GAM (reaction zone) . During a brief (two minute) incubation the Rat anti-E2 binds to the GAM. Next, 50 μL of E2-ALP conjugate were added to about the center of the reaction zone. The E2-ALP binds to the Rat anti-E2. Next, about 75 μL of substrate/wash were applied to about the center of the reaction zone. The substrate/wash elutes any unbound material away from the reaction zone and simultaneously the reaction between the bound ALP and the substrate is initiated forming a fluorescent product. The fluorescent response from a finite portion of the reaction zone was determined using a front surface fluorometer.

The solution which gave the highest response was selected as being optimal since the most antibody is captured per unit GAM. Here that solution is 2.5%

GAM. See Figure 1 and Table 1. Multiple tabs of the glass fiber filter paper were spotted using the 2.5%

GAM solution in the method described above.

TABLE 1 % GAM Versus Response of Calibrator A

% GAM RESPONSE OF CALIBRATOR A

0.0 180

0.5 5699

1.0 8200 1.5 9471

2.0 9956

2.5 10104

3.0 8622

3.5 9470 4.0 9188

4.5 9853

5.0 8700

5.5 8494

6.0 8544 6.5 8057

This technique can be used with antibodies from the same species or homologous species by performing simple binding or affinity studies. A. Cabat, Structural Concepts in Immunology and Immunochemistry, (2nd Ed. 1976):80-94. Here, goat anti-mouse immunoglobulin was immobilized on the tabs even though the antibody against Estradiol was an anti-rat monoclonal. This takes advantage of interspecies homology and makes the immunoreactant solid phase ("tab") more truly "universal". Other examples of interspecies homology are between sheep/goat or horse/donkey. This widens the field of available antibodies so that the best antibody can be selected. Also, as can readily be appreciated the immunoglobulin spotted on the tab could be from the rat with the estradiol specific antibody coming from a mouse, the reverse of the method described above, which again increases the choice of available antibodies. Optimization of the Rat Anti-Estradiol Concentration The optimal rat anti-estradiol antibody (rat anti-E2) was determined using the 2.5% GAM tabs prepared as described above. The rat anti-E2 was diluted to various concentrations in 50mM Tris, pH 8.0, containing 0.1% bovine serum albumin. The dilutions were as follows: 1:50, 1:60 and 1:75. It is readily apparent that wider or narrower dilutions may be evaluated (i.e., 1:10, 1:100, 1:1000 and 1:10,000 or 1:2, 1:3, 1:5 respectively) depending on the antibody being evaluated and the nature of that antibody. The concentrations were evaluated as follows: One hundred microliters of each dilution of rat anti-E2 were added to cups containing 100 μL of A(0) calibrator and cups containing 100 μL of B(20 pg/mL) calibrator. The mixtures were incubated at room temperature for fifteen minutes. The time and temperature for incubation may be varied according to the requirements for the assay. Preferred ranges are from 0 to 4 hours and 18 to 37 degrees C. After the incubation 150 microliter aliquots of the mixtures were added to the tabs in the zone containing the GAM (reaction zone) . During a brief (two minute) incubation the Rat anti-E2 binds to the GAM. Next, 50 μL of E2-ALP conjugate was added to about the center of the reaction zone. The E2-ALP binds to the Rat anti-E2. Next, about 75 μL of substrate/wash were applied to about the center of the reaction zone. The substrate/wash elutes any unbound material away from the reaction zone and simultaneously the reaction between the bound ALP and the substrate is initiated forming a fluorescent product. The fluorescent response from a finite portion of the reaction zone was determined using a front surface fluorometer. The optimal dilution of rat anti-E2 was selected by measuring two parameters. The first parameter is fluorescent response generated when the A(0) calibrator is assayed with each dilution of rat anti- E2. The fluorescent response is directly proportional to the amount of rat anti-E2 captured by the GAM. Accordingly, these responses are indirectly proportional to the amount of E2 in the sample (characteristic of a competitive assay) . The second parameter measured is the ratio of the fluorescent response from the B calibrator (20 pg/mL) over the fluorescent response from the A(0) calibrator (B/A ratio) . Low B/A ratios indicate that there is a measurable difference between these two calibrator levels. The rat anti-E2 dilution which gives the highest fluorescent response using the A(0) calibrator with the smallest B/A ratio is chosen as optimal. Results are shown in Table 2 below. TABLE 2 Dilution of Rat anti-E2 1:50 1:60 1:75

Fluorescent response 9012 6898 6024 from A.O. Calibrator

Fluorescent response 8351 7097 6234 from B.20 pg/mL Calibrator Ratio of B/A 0.93 1.02 1.03 As is readily apparent from Table 2 above the highest Calibrator A rate with the lowest Calibrator B/A ratio occurs using the 1:50 dilution of Rat anti- E2. The other dilutions show no differentiation between these two levels of calibrators hence are not useful in a diagnostic assay of Estradiol. Using the above data the 1:50 dilution was chosen to perform assay of Estradiol.

A standard curve was constructed using the calibrators designated in the materials section above. Assay Format

In this assay format, the antibody-antigen complex is formed by adding 100 μl of the 1:50 dilution of Rat estradiol monoclonal antibody in solution and 100 μl of serum^'sample or calibrator to a STRATUS* (Baxter Diagnostics Inc.) cup. This mixture, which now contains antigen-antibody complex as well as uncomplexed antibody, is then added directly to the center of the multi-test goat anti- mouse reagent matrix which captures the free estradiol antibody as well as estradiol-antibody complex that was formed in the STRATUS* (Baxter Diagnostics Inc.) cup. The reagent matrix is then moved to a second work station where 50 μl of the E2 conjugate is added to the center of the matrix. The conjugated E2 combines with any unoccupied binding sites of the immobilized estradiol antibody. Next, enzyme activity is initiated at the same time that bound and free material partitioned by addition of 78 μl of substrate/wash solution III.

All the above reagent additions are made directly to the center of the multi-test goat anti-mouse reagent matrix so that the addition of reagent also serves to separate any unbound materials away from the center of the tab. Finally, front surface fluorometry is used to measure bound enzyme rate. The observed rates are inversely proportional to the concentration of sample E2 and are converted to clinical units by comparison to a stored standard curve. As noted above one of the factors that limits sensitivity is the time the sample has for interaction with the anti-estradiol antibody. After the anti- estradiol antibody is mixed with the sample it can be either applied directly to the tab with no incubation or can be incubated for a time if the sensitivity should be increased. This particular example uses an incubation of fifteen minutes.

Example II - Goat-anti-rabbit Multi-test Reagent Used in an Assay for Estradiol Below is a description of the multi-test reagent materials and assay format using goat-anti-rabbit antibody with normal rabbit serum And a rabbit anti- estradiol antibody. Following that is a comparison of the current STRATUS (Baxter Diagnostics Inc.) calibration curve with a multi-test estradiol calibration curve. Material*

E2 conjugate: an £2-ALP conjugate was prepared using the standard mixed anhydride method. It was then diluted to a concentration of 1.2 μg/mL in a Tris buffer at pH 7.0.

£2 calibrators: £2 stock solution, approximately 100 μg/mL of £2 in 80% ethanol was prepared. Aliquots of the £2 stock were added to charcoal stripped human serum to produce a set of £2 calibrators at 0 (A) , 50 (B) , 100 (C) , 500 (D) , 1000 (£) , and 2500 (F) pg/mL. £2 assay diluent: 100 mM acetate, pH 4.5, containing 0.1% CHAPSO and 350 μg/mL 8-anilino-l- naphthalene sulfonic acid.

Substrate/Wash: a solution containing ImM 4- ■βthylumbellifβryl phosphate in diethanolamine buffer, pH 9.0.

Rabbit anti-E2 antibody from Diagnostic Systems Laboratories, Inc. Tab Optimization Solution A was prepared by diluting normal rabbit serum to 1% in a 50 M Tris buffer, pH 8, containing 0.5% Zonyl FSN. Solution B was prepared by dilution goat anti-rabbit immunoglobulin to 1.2% in the above buffer. One mL of Solution A was added to each of 13test tubes, labeled 1 to 13. Then, beginning with 0.5mL in tube 1, Solution B was added in 0.1 mL increment to tubes 2 to 13 (Titration tubes) . After an overnight incubation at 25°C to effectuate formation of a goat anti-rabbit/normal rabbit serum complex the solutions were filtered through .8 μm filter to remove particulates. About 75 μl aliquots from each of the thirteen tubes were applied to glass fiber paper tabs and dried. Here drying was accomplished at 80°C. To determine the optimal complex, the tabs were assayed as described below using a zero calibrator as the patient sample. The optimal goat anti-rabbit/normal rabbit serum complex contains enough binding capacity for immobilization of the rabbit-anti-estradiol antibody. An example of the titration is shown in Fig.2; the conditions used for Tube 5 (.9 parts B/l part A) were selected for tab production because they gave the highest response. Rabbit anti-Estradiol Optimization

The rabbit anti-estradiol antibody was titered using the optimal goat anti-rabbit/normal rabbit serum tabs described above. The titer was accomplished by serially diluting the rabbit anti-estradiol antibody in a 50 mM Tris buffer, pH 8, containing 0.1% bovine serum albumin and 0.1% (3-[chloamidopropyl)- dimethylammonio]-2-hydroxy-l-propane sulfonate) and were assayed as described below. The optimal dilution of rabbit anti-estradiol was selected by measuring two parameters. The first parameter is fluorescent response generated when the A(0) calibrator is assayed with each dilution of rabbit anti-estradiol. The fluorescent response is directly proportional to the amount of rabbit anti-estradiol captured by the GAR. Accordingly, these responses are indirectly proportional to the amount of estradiol in the sample (characteristic of a competitive assay) . The second parameter measured is the result of subtracting the fluorescent response of the F (2500 pg/mL) calibrator from the fluorescent response of the B (50 pg/mL) calibrator. (Cal B - Cal F) . The dilution which gives the maximal difference is a measure of sensitivity. The dilution which produced maximal Calibrator A response and maximal Calibrator B response minus Calibrator F response was determined and this dilution was chosen as the optimal dilution for the rabbit anti-estradiol. An example of the titration is shown in Fig.3; the 1:7500 dilution was selected as optimal. Assay Format

In this assay, serum estradiol is extracted from endogenous binding proteins by adding 50 μl of E2 Assay Diluent to 25 μl of patient sample, control or calibrator. Then, the binding reaction is initiated by addition of 25 μl of the 1:7500 dilution of rabbit anti-estradiol to the extracted sample followed by a 15 minute incubation of the samples at 25°C. Following the incubation about 76 μl of the sample is immediately applied to the glass-fiber paper tab which had been prepared with the goat anti-rabbit/normal rabbit serum complex that gave the highest response. Sample application is directed to the center of the dried complex. The tab is moved to a second work- station where about 60 μl of the estradiol conjugate is added to about the center. The conjugate combines with unoccupied binding sites of immobilized estradiol antibody. Next, the tab is moved to a third work station and enzyme activity is initiated and simultaneously free and bound material are radially partitioned by addition of about 70 μl of sub¬ strate/wash solution III to the center. Finally, front surface fluorometry is used to measure fluorescent rates. Responses are inversely pro- portional to the concentration of sample E2 and are converted to clinical units by comparison to a stored standard curve.

Example 3 - Comparative Tab Performance In Fig.4 the current STRATUS* (Baxter Diagnostics Inc.) and multi-test tab calibration curves are compared. There is significant improvement in curve slope (sensitivity) of estradiol values less than 500 pg/ml with the multi-test tabs. However, the current STRATUS* (Baxter Diagnostics Inc.) tab's performance is better (slope is greater) for estradiol values of greater than 1000 pg/mL. Fig.5 compares the response per unit of estradiol for values of less than 100 pg/mL; the greater the change the more sensitive the assay. Here, the multi-test tab demonstrates improved performance over STRATUS* (Baxter Diagnostics Inc.) . Example 4 - Goat Anti-mouse Multi-test Reagent Used in An Assay for hCG

Below is a description of the multi-test reagent materials and means for determining optimum concentrations of goat anti-mouse antibody and a mouse anti-hCG antibody to be used in an assay for hCG.

Materials: Anti-hCG conjugate: an anti-hCG antibody conjugate of alkaline phosphatase (ALP) and antibody to hCG were prepared using a standard method using sulfo-SIAB (sulfo-succimimidyl (4-iodoacetyl)- aminobenzoate sodium salt and coupled to reduced anti- hCG Fab' antibody. The resulting conjugate was diluted to about 180 ng/mL in buffer with 0.1% sodium azide as a preservative. hCG Calibrators: an hCG stock solution of 12 million mlU/mL in distilled water was prepared. Aliquots of the hCG stock were added to normal hCG free human serum to produce a set of hCG calibrators at 0(A), 5(B), 15(C), 50(D), 150(E), and 500(F) miu/mL.

Preparation and optimization of goat anti-mouse multi-reagent: solutions of 1 to 10% goat anti-mouse (GAM) , at 1% increments, diluted in a 50 mM Tris buffer, pH 8.0, containing 0.5% ZONYL FSN (a surfactant manufactured by DuPont) are prepared. The solutions are then filtered with a .85 μ filter to remove particulates. Multiple tabs of glass fiber filter (Whatman GF/F) are spotted with about 76 μl of each solution and dried.

The glass fiber filters spotted with the incremental solutions of GAM are evaluated as follows: about a one hundred microliter aliquot of about a 1:100 dilution of mouse anti-hCG antibody are added to about 100 μl of an (F) calibrator. In a brief incubation, the hCG in the F calibrator binds to the anti-hCG antibody. About 100 μl of the incubation mixture are added to the tabs in the zone containing the GAM (reaction zone) . During a brief (about two minutes) incubation the mouse anti-hCG binds to the GAM. Next, about 50 μl of anti-hCG antibody conjugate are added to about the center of the reaction zone. The conjugate binds to the hCG which is bound to the anti-hCG antibody, which in turn is bound to the GAM on the tab of glass fiber filter paper. Next, about 75 μl of substrate-wash are applied to about the center of the reaction zone. The substrate-wash elutes any unbound material away from the reaction zone and simultaneously the reaction between the bound ALP and the substrate is initiated forming a fluorescent product. The fluorescent response from a finite portion of the reaction zone is determined using a front surface fluorometer.

The solution of maximum Calibrator F response is selected as being optimal since the most antibody is captured per unit GAM. Multiple tabs of the glass fiber filter paper are spotted using the solution which gives the maximal response in the method described above.

Optimization of the mouse anti-hCG antibody concentration: the optimal mouse anti-hCG antibody is determined using the GAM tabs prepared as described above. The mouse anti-hCG antibody is diluted to various concentrations in 50 mM Tris, pH 8.0, containing 0.1% bovine serum albumin. The concentrations evaluated are as follows: 1:100, 1:200 and 1:500. It is readily apparent that wider or narrower concentrations may be evaluated (ie., 1:10, 1:100, 1:1000 and 1:10,000 or 1:2, 1:3, and 1:5 respectively) depending on the antibody being evaluated and the nature of that antibody. The dilutions are evaluated as follows: about 100 μl of each dilution of mouse anti-hCG antibody are added to cups containing 100 μl of F (500 mlU/mL) calibrator, cups containing 100 μl of B (5 mlU/mL) calibrator and 100 μl of A (0) calibrator. The mixtures are incubated at room temperature for fifteen minutes. The time and temperature for incubation may be varied according to the requirements for the assay. Pre¬ ferred ranges are from 0 to 4 hours and 18 to 37 degrees Celsius. After the incubation, 100 μl aliquot of the mixtures are added to the tabs in the reaction zone. During a brief incubation the mouse anti-hCG antibody (bound and unbound) binds to the GAM. Next, 50 μl of anti-hCG conjugate is added t© about the center of the reaction zone. The conjugate binds to any hCG in the reaction zone. Next, about 75 μl of substrate-wash are applied to about the center of the reaction zone. The substrate-wash elutes any unbound material away from the reaction zone and simultaneously the reaction between the bound ALP and the substrate is initiated forming a. fluorescent product. The fluorescent response from a finite portion of the reaction zone is determined using a front surface fluorometer. The optimal concentration of mouse anti-hCG antibody is selected by measuring two parameters. The first parameter is fluorescent response generated when the F(500 mlU/mL) calibrator is assayed with each concentration of mouse anti-hCG antibody. The fluorescent response is directly proportional to the amount of anti-hCG antibody captured by the GAM. Accordingly, these responses are also directly proportional to the amount of hCG in the sample (characteristic of a sandwich assay) . The second paramater measured is the ratio of the fluorescent response from the B calibrator (5 miu/mL) over the fluorescent response from the A(0) calibrator (B/A ratio) . High B/A ratios indicates that there is a measurable difference between these two calibrator levels. The anti-hCG antibody concentration which gives the highest fluorescent response using the F(500 miu/mL) calibrator with the highest B/A ratio is chosen as optimal. Alternatively, the anti-hCG antibody can be optimized first by using tabs of glass fiber filter paper that have been prepared with 76 μl of an excess amount of GAM (ie. , % of GAM that is greater than the % of GAM which gave the maximal Calibrator A response) . After the anti-hCG is optimized, the GAM can be optimized in the procedure described above.

Assay format: In this assay format, the antibody-antigen complex is formed by adding 100 μL of the optimum anti-hCG antibody in solution and 100 μL of serum sample, calibrator or control to a STRATUS" (Baxter Diagnostics Inc.) cup. One hundred microliters of this mixture which now contains antigen-antibody complex as well as uncomplexed antibody, is then added directly to about the center of multi-test goat anti-mouse reagent matrix which captures the antigen-antibody complex that was formed as well as an uncomplexed antibody. The reagent matrix is then moved to a second work station where 50 μL of the conjugate is added to about the center of the matrix. The conjugate combines with the bound hCG. Next, enzyme activity is initiated at the same time that bound and free material are partitioned by addition of 76 μL of substrate/wash solution. All the above reagent additions are made to about the center of the multi-test goat anti-mouse reagent matrix so that the addition of reagent also serves to separate any unbound materials away from the center of the reaction zone. Finally, front surface fluoro etry is used to measure bound enzyme rate. The observed rates are proportional to the concentration of sample hCG and are converted to clinical units by comparison to a standard curve. Example 5 Example 2 is repeated except that the antibody on the glass fiber filter paper comprises about a 76 μl aliquot of the proper final concentrations of the GAR of Example 2 and the GAM of Example 4. The optimi¬ zation of concentration of the GAR and GAM which are applied to the glass fiber filter paper are determined by the procedures set forth in Example 2 (for the GAR) and Example 4 (for the GAM) . Optimization of the rat anti-estradiol antibody concentration is determined as per Example 2. The concentration of serum samples, calibrators, and controls are determined as per the assay format of Example 2. Example 6

Example 4 is repeated except that the antibody on the glass fiber filter paper comprises the GAR of Example 2 and the GAM of Example 4. The optimization of concentrations of the GAR and GAM which are applied to the glass fiber filter paper are determined by the procedures set forth in Example 2 (for the GAR) and Example 4 (for the GAM) . Optimization of the mouse anti-hCG antibody concentration is determined as per Example 4. The concentration of serum sample, calibrator, or control is determined as per the assay format of Example 4. Examples 7-11

Examples 2 and 4-6 are repeated respectively except that the specific antibody (ie., anti-hCG antibody, anti-E2 antibody etc.) is added to the multi-test reagent prior to the addition of the sample containing the analyte. Although the invention has been described primarily in connection with special and preferred embodiments, it will be understood that it is capable of modification without departing from the scope of the invention. The following claims are intended to cover all variations, uses, or adaptations of the invention, following, in general, the principles thereof and including such departures from the present disclosure as come within known or customary practice in the field to which the invention pertains, or as are obvious to persons skilled in the field.

Claims

WE CLAIM:

1. An immunochemical reagent comprising secondary antibodies adsorbed on to an inert porous medium.

2. The composition of Claim 1 wherein said secondary antibodies are goat anti-mouse immunoglobulins.

3. The composition of Claim 1 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulins.

4. A human immunochemical reagent comprising: antiserum to specific animal species adsorbed on to an inert porous medium.

5. The composition of Claim 4 wherein said antiserum is goat anti-mouse immunoglobulin.

6. The composition of Claim 4 wherein said antiserum is goat anti-rabbit immunoglobulin.

7. The composition of Claim 5 wherein about 3% goat anti-mouse immunoglobulin adsorbed on to an inert porous medium.

8. The reagent of Claim 4 wherein said antiserum is comprised of goat anti-rabbit and goat anti-mouse immunoglobulin.

9. The reagent of Claim 4 wherein said antiserum is complexed with normal animal serum.

10. The reagent of Claim 6 wherein said goat antiserum is complexed with normal rabbit serum.

11. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of a secondary antibody immobilized on a solid support, the method comprising: a. combining under binding conditions a fluid sample containing said analyte and primary antibodies to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; b. applying said fluid mixture under binding conditions to said solid support to bind analyte-primary antibody complexes and uncomplexed primary antibodies; c. applying an indicator to said solid support under binding conditions to bind with bound uncomplexed antibodies; d. observing the extent to which the indicator is present on said solid support; and e. correlating the extent to which said indicator is present on said solid support with the amount of unknown analyte in said sample.

12. The method of Claim 11 wherein said secondary antibodies are goat anti-rabbit.

13. The method of Claim 11 wherein said secondary antibodies are goat anti-mouse.

14. The method of Claim 11 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

15. The method of Claim 11 wherein said indicator consists essentially of an enzyme labeled analyte and a substrate wash solution.

16. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of secondary antibodies immobilized within a finite zone of the interstices of a solid, inert porous support, the method comprising: a. combining under binding conditions a fluid sample containing said analyte and primary antibodies to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; b. applying said fluid mixture under binding conditions to the center of said finite zone to bind analyte-primary antibody complexes and uncomplexed antibodies; c. applying an indicator to said solid support under binding conditions to bind with uncomplexed antibodies; d. observing the extent to which the indicator is present within a delimited area of said reaction zone; and e. correlating the extent to which said indicator is present in said delimited area with the amount of unknown analyte in said sample.

17. The method of Claim iβ wherein said indicator consists essentially of an enzyme labeled analyte and a substrate wash solution.

18. The method of Claim 16 wherein said secondary antibodies are goat anti-rabbit.

19. The method of Claim 16 wherein said secondary antibodies are goat anti-mouse.

20. The method of Claim 16 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

21. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of a secondary antibody immobilized on a solid support, the method comprising: a. applying under binding conditions primary antibody to said solid support; b. applying under binding conditions said fluid sample to said solid support; c. applying an indicator to said solid phase under binding conditions to bind with bound uncomplexed antibodies; d. observing the extent to which the indicator is present on said solid support; and e. correlating the extent to which said indicator is present on said solid support with the amount of unknown analyte in said sample.

22. The method of Claim 21 wherein said secondary antibodies are goat anti-rabbit.

23. The method of Claim 21 wherein said secondary antibodies are goat anti-mouse.

24. The method of Claim 21 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

25. The method of Claim 21 wherein said indicator consists essentially of an enzyme labeled analyte and a substrate wash solution.

26. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of secondary antibodies immobilized within a finite zone of the interstices of a solid, inert porous support, the method comprising: a. applying under binding conditions primary antibody to the center of said finite zone of said solid support; b. applying under binding conditions said fluid sample to the center of said finite zone of said solid support; c. applying an indicator to said solid support under binding conditions to bind with uncomplexed antibodies; d. observing the extent to which the indicator is present within a delimited area of said reaction zone; and e. correlating the extent to which said indicator is present in said delimited area with the amount of unknown analyte in said sample.

27. The method of Claim 26 wherein said indicator consists essentially of an enzyme labeled analyte and a substrate wash solution.

28. The method of Claim 26 wherein said secondary antibodies are goat anti-rabbit.

29. The method of Claim 26 wherein said secondary antibodies are goat anti-mouse.

30. The method of Claim 26 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

31. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of a secondary antibody immobilized on a solid support, the method comprising: a. combining under binding conditions a fluid sample containing said analyte, said primary antibodies and an indicator to bind with antibodies; to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; b. applying said fluid mixture under binding conditions to said solid support to bind analyte-primary antibody complexes and uncomplexed primary antibodies; c. observing the extent to which the indicator is present on said solid support; and d. correlating the extent to which said indicator is present on said solid support with the amount of unknown analyte in said sample.

32. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of a secondary antibody immobilized on a solid support, the method comprising: a. combining under binding conditions a fluid sample containing said analyte and primary antibodies to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; b. applying said fluid mixture under binding conditions to said solid support to bind analyte-primary antibody complexes and uncomplexed primary antibodies; c. applying an indicator to said solid support under binding conditions to bind with bound analytes; d. observing the extent to which the indicator is present on said solid support; and e. correlating the extent to which said indicator is present on said solid support with the amount of unknown analyte in said sample.

33. The method of Claim 32 wherein said secondary antibodies are goat anti-rabbit.

34. The method of Claim 32 wherein said secondary antibodies are goat anti-mouse.

35. The method of Claim 32 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

36. The method of Claim 32 wherein said indicator consists essentially of an enzyme labeled antibody for said analyte and a substrate wash solution.

37. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of secondary antibodies immobilized within a finite zone of the interstices of a solid, inert porous support, the method comprising: a. combining under binding conditions a fluid sample containing said analyte and primary antibodies to form a fluid mixture of analyte-primary antibody complexes and uncomplexed primary antibodies; b. applying said fluid mixture under binding conditions to the center of said finite zone to bind analyte-primary antibody complexes and uncomplexed antibodies; c. applying an indicator to said solid support under binding conditions to bind with bound analyte; d. observing the extent to which the indicator is present within a delimited area of said reaction zone; and e. correlating the extent to which said indicator is present in said delimited area with the amount of unknown analyte in said sample.

38. The method of Claim 37 wherein said indicator consists essentially of an enzyme labeled antibody for said analyte and a substrate wash solution.

39. The method of Claim 37 wherein said secondary antibodies are goat anti-rabbit.

40. The method of Claim 37 wherein said secondary antibodies are goat anti-mouse.

41. The method of Claim 37 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

42. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of a secondary antibody immobilized on a solid support, the method comprising: a. applying under binding conditions primary antibody to said solid support; b. applying under binding conditions said fluid sample to said solid support; c. applying an indicator to said solid phase under binding conditions to bind with bound analyte; d. observing the extent to which the indicator is present on said solid support; and e. correlating the extent to which said indicator is present on said solid support with the amount of unknown analyte in said sample.

43. The method of Claim 42 wherein said secondary antibodies are goad anti-rabbit.

44. The method of Claim 42 wherein said secondary antibodies are goat anti-mouse.

45. The method of Claim 42 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.

46. The method of Claim 42 wherein said indicator consists essentially of an enzyme labeled antibody for said analyte and a substrate wash solution.

47. A method for conducting a solid phase immunoassay of a fluid sample for an unknown amount of analyte, said solid phase consisting essentially of secondary antibodies immobilized within a finite zone of the interstices of a solid, inert porous support, the method comprising: a. applying under binding conditions primary antibody to the center of said finite zone of said solid support; b. applying under binding conditions said fluid sample to the center of said finite zone of said solid support; c. applying an indicator to said solid support under binding conditions to bind with bound analyte; d. observing the extent to which the indicator is present within a delimited area of said reaction zone; and e. correlating the extent to which said indicator is present in said delimited area with the amount of unknown analyte in said sample.

48. The method of Claim 47 wherein said indicator consists essentially of an enzyme labeled antibody for said analyte and a substrate wash solution.

49. The method of Claim 47 wherein said secondary antibodies are goat anti-rabbit.

50. The method of Claim 47 wherein said secondary antibodies are goat anti-mouse.

51. The method of Claim 47 wherein said secondary antibodies are goat anti-rabbit and goat anti- mouse immunoglobulin.