Diagnostic test kit and specific binding assay using a peroxidase label and a modulator of signal

Abstract: The signal generated in a specific binding assay wherein a peroxidase label is used to detect the resulting specific binding complex can be modulated by contacting the signal forming reagents with a buffered solution of a hydroxamic acid or acyl hydrazine having the structure R-CO-NH-R' or an equivalent salt thereof, wherein R is aryl of 6 to 10 carbon atoms in the aromatic nucleus, alkyl of 1 to 7 carbon atoms, cycloalkyl of 5 to 10 carbon atoms in the ring or aromatic heterocyclyl of 5 to 10 atoms in the ring, at least one of which is an oxygen, nitrogen or sulfur atom, and R' is hydroxy or amino. This solution can be provided in a diagnostic test kit for use in various methods to detect a specific binding ligand. The result is improved signal stability and lowered background.

Description: The present invention relates to a diagnostic test kit comprising a compound which modulates the signal resulting from the action of a peroxidase on its substrate. The invention is also directed to a method for determining a specific binding ligand using, among other reagents, the modulating compound. There is a continuous need in medical practice, research and diagnostic procedures for rapid, accurate and qualitative or quantitative determinations of biological substances which are present in biological fluids at low concentrations. For example, the presence of drugs, narcotics, hormones, steroids, polypeptides, prostaglandins or infectious organisms in blood, urine, saliva, vaginal secretions, dental plaque, gingival crevicular fluid and other biological specimens has to be determined in an accurate and rapid fashion for suitable diagnosis or treatment. To provide such determinations, various methods have been devised for isolating and identifying biological substances employing specific binding reactions between the substance to be detected (identified herein as a "specific binding ligand") and a compound specifically reactive with that substance (sometimes identified as a "receptor" for the ligand). The complex formed between ligand and receptor can be detected by a variety of known methods. The most commonly used methods employ a signal-generating moiety of some type which is either already attached to one of the components of the complex, or becomes part of the complex through further reaction. For example, in the formation of a complex of biotin with avidin, the complex may be detected using a label on either the avidin or biotin molecule. Such a label can be a radioisotope or an enzyme conjugated with the avidin or biotin. Alternatively, the avidin-biotin complex might be detected by further reaction with a labeled molecule which is specific to either or both parts of the complex. It is commonly known to do the same with antigens and their corresponding antibodies. Preferred labels in specific binding reactions are clearly enzymes because the handling and disposal problems associated with radioisotopes can be avoided. Many enzymes are known to be useful in this context with peroxidases being the most common. In diagnostic tests designed to be rapid and easy to use with moderate training in a doctor's office or clinic, the specific binding ligand of interest (such as an antigen from an infectious agent) is often detected using colorimetric or chemiluminescent signals resulting from reaction of the enzyme label with its corresponding substrate. There is a need to produce the signal quickly and intensely if the ligand is present. However, there is also a need to have the signal produced in a defined region of a test zone in a test device so an adjacent or surrounding region could be used as a background control. In such cases, production of the signal should be modulated or stopped after a certain period of time in order to provide clear distinction between test zone and background zone. An advance in the art in the detection of microorganisms associated with periodontal diseases is described and claimed in EP-A-0 439 210. This case describes the simultaneous detection and differentiation of these microorganisms, and particularly Actinobacillus actinomycetemcomitans , Porphyromonas gingivalis (formerly known in the art as Bacteroides gingivalis ) and Prevotella intermedia (formerly known as Bacteroides intermedius ), in an immunometric (also known as "sandwich") assay using water-insoluble reagents in defined regions of a microporous filtration membrane. The simultaneous detection and differentiation of these microorganisms have considerable clinical and commercial significance. The assay described in EP-A-0 439 210 is carried out using peroxidase as a label on antibodies specific for the bacterial antigen. It is well known in such assays to use a buffered solution of sodium azide to stop the production of colorimetric signal when peroxidase reacts with a suitable substrate. In most instances, a low concentration (for example, 0.1 weight percent) of sodium azide performs satisfactorily. However, it has been observed that when sodium azide is used at high pH, the production of colorimetric signal is not stopped completely, especially if the signal is to be detected on a porous matrix where reagents can readily migrate. In other words, the colorimetric signal production is slowed down by the azide but not stopped. This causes the specific signal and the surrounding region on the porous matrix to continue to develop signal. It is desired to prevent this from happening. It was considered to use greater concentrations of sodium azide to solve the problem, but this was not acceptable because sodium azide is a well known toxic material and also has explosive properties. The noted problem has been solved using a diagnostic test kit comprising a water soluble, peroxidase-labeled specific binding species, the kit characterized as further comprising, separately packaged, a buffered composition comprising at least 0.05 weight percent of a compound having the structure R-CO-NH-R' or an equivalent salt thereof, wherein R is phenyl, alkyl having 1 to 4 carbon atoms or cycloalkyl having 5 or 6 carbon atoms in the ring, and R' is hydroxy. Moreover, a method for the determination of a specific binding ligand comprises: A. reacting a specific binding ligand from a biological specimen with a water soluble receptor specific for said ligand, the receptor being labeled with peroxidase, to form a peroxidase-labeled specific binding complex between the ligand and receptor, B. prior to, simultaneously with or subsequently to step A, insolubilizing the specific binding ligand so as to provide an insolubilized specific binding complex, C. contacting the insolubilized complex with a composition for providing a colorimetric or chemiluminescent signal in response to peroxidase in the complex, and D. modulating and detecting the level of the signal by contacting the insolubilized complex with a composition comprising at least 0.05 weight percent of a compound having the structure R-CO-NH-R' or an equivalent salt thereof, wherein R is phenyl, alkyl having 1 to 4 carbon atoms or cycloalkyl having 5 or 6 carbon atoms in the ring, and R' is hydroxy. The invention provides an effective means for modulating or stopping the production of a colorimetric or chemiluminescent signal produced by enzymatic reaction in specific binding assays. This effectiveness is particularly apparent when peroxidase is the enzyme of concern. In assays carried out on a microporous membrane, the colorimetric signal from reagents on or above the membrane, or from reagents that flow back through the membrane is virtually eliminated, and the assays can be used semi-quantitatively. These advantages are achieved by contacting the insolubilized specific binding complex, having a peroxidase label therein, with a hydroxamic acid or acyl hydrazine as defined herein. Depending upon the concentration of acid used, the production of signal from the enzymatic reaction with its substrate can be stopped completely or modulated to slow the reaction rate. The compounds used in the practice of this invention are hydroxamic acids represented by the following structure: R-CO-NH-R' or an equivalent salt thereof wherein R' is hydroxy. These compounds can also be in the form of hydroximic acids [that is, R-C(=NOH)-OH], and can exist in two isomeric forms. R is phenyl, substituted or unsubstituted alkyl of 1 to 4 carbon atoms e.g. methyl, ethyl, isopropyl and butyl, or cycloalkyl of 5 or 6 carbon atoms in the ring e.g. cyclopentyl and cyclohexyl. Preferred compounds are benzohydroxamic acid and equivalent salts. For all of the acids described herein, equivalent salts include ammonium salts, alkali metal salts and alkaline earth metal salts. The hydroxamic acids defined above can be readily prepared using known starting materials and chemical synthetic methods such as the reaction of hydroxylamine with acyl halides. The compound described herein is provided in a buffered solution at a concentration of at least 0.05 percent based on total solution weight. Generally, the amount of compound is in the range of from 0.05 to 5 weight percent, with from 0.05 to 1 weight percent being preferred. A mixture of hydroxamic acids or salts can be used if desired. Generally, the hydroxamic acid described herein is buffered to a pH of from 6 to 11 using one or more suitable buffers including, but not limited to, phosphate, 3-(4-morpholino)propanesulfonic acid, 2-(4-morpholino)ethanesulfonic acid, glycine and others readily apparent to one skilled in the art. Addenda which may optionally be included in the buffered composition of compound include inorganic salts, surfactants and polymeric materials. The buffered composition described above is generally supplied as part of a diagnostic test kit having a number of separately packaged reagents, compositions and equipment needed for a given assay. However, the buffered composition can be provided by itself or prepared at the time of the assay. Typical diagnostic kit components, however, include a water-soluble peroxidase-labeled specific binding species, wash solutions, extraction compositions, signal-providing compositions, disposable test devices and others readily apparent to one of ordinary skill in the art. The specific binding species in the test kit can be any molecule from a biological or chemical source which reacts specifically with a ligand of interest. For example, the species can be avidin or a derivatized form thereof, biotin or a derivatized form thereof, antibody, antigenic material, a hapten, sugar, lectin or other chemical or biological compound which has a receptor as that term is understood in the art. In the context of this invention, a nucleic acid is also considered a specific binding species which "complexes" (or hybridizes) with a complementary nucleic acid which is considered a ligand in this instance. Preferably, the water-soluble peroxidase-labeled species included in the test kit is an antibody. Preferably, the species is labeled with a peroxidase from any of animal, plant, fungal or bacterial source. Procedures for attaching peroxidase to specific binding species are also well known (including for example, Yoshitake et al, Eur.Biochem. , 101 , pp. 395-399, 1979). The method of this invention can be used to determine a specific binding ligand of interest. Such ligands include oligonucleotides, nucleic acids, proteins, carbohydrates, lipopolysaccharides, peptides, polypeptides, polysaccharides, glycolipids, glycoproteins and any components of these materials. Such ligands can be detected in any human or animal biological fluid or specimen including whole blood, sera, plasma, lymphatic fluid, bile, urine, spinal fluid, seminal fluid, vaginal secretions, sputum, perspiration, stool specimens, tissue preparations, dental plaque, saliva, gingival crevicular fluid and semen. The invention is particularly useful for the detection of microorganisms associated with periodontal diseases found in saliva, dental plaque, gingival crevicular fluid and other oral fluids or specimens. In particular, the microorganisms Actinobacillus actinomycetemcomitans , Prophyromonas gingivalis and Prevotella intermedia are determined, either individually or collectively, using the present invention. However, other microorganisms which are suspected of being associated with periodontal diseases can also be detected or differentiated with this invention. Such other microorganisms include Wolinella recta , Bacteroides forsythus , Eikenella corrodens , Fusobacterium nucleatum and Troponema denticola . Before considering the first step of the method of this invention, it should be understood that prior to step A there can be a wide variety of procedures carried out for specimen preparation, purification or extraction of antigen or nucleic acid. One useful procedure which can be carried out to increase the sensitivity of nucleic acid detection is known in the art as polymerase chain reaction (PCR). The details of this process are provided for instance, in US-A-4,683,202. Once a nucleic acid has been amplified by this technique, various detection means can be employed including the use of a peroxidase-labeled probe. The enzyme label can then be used for providing an appropriate detectable signal which can be modulated using the present invention. In the practice of this invention, the specific binding ligand in a biological specimen (or a ligand obtained therefrom) is reacted with a water-soluble receptor specific for the ligand. The receptor is labeled with a peroxidase as noted above. A specific binding complex which is labeled with the enzyme is thereby formed. Complex formation typically occurs in solution, but the type of container or vessel in which it occurs is not critical. In some cases, the complex is formed in the crude specimen after lysis or other extraction procedures. In other cases, the complex is formed on a special substrate, plate or membrane which can "capture" the complex in some manner. Contact can occur at a wide range of temperatures, for example from below room temperature to those near the boiling point of water as long as the components of the complex are not adversely affected. The reagents are contacted by mixing in some fashion so there is opportunity for the reactants to form the complex. Prior to, simultaneously with or subsequently to step A, the specific binding ligand is insolubilized so the resulting complex is also insolubilized and can be removed from solution in a suitable manner. This means that the format for the assay can be of a wide variety of forms that have been developed over the years. In one embodiment, a specific binding ligand (for example an extracted antigen) can be insolubilized by direct adsorption or covalent attachment to a solid material, such as polymeric or glass particles, filtration membranes, cellulosic filter papers, solid polymeric or resin-coated films, glass slides or walls of test tubes, glass or polymeric cuvettes and other materials. Such assays are generally known in the art as "direct binding" assays whereby the specific binding ligand directly binds to the material, and peroxidase-labeled receptor molecules (such as antibodies) are used to complex with the insolubilized ligand. Alternatively, the receptor can be unlabeled and a second receptor which is labeled with peroxidase and specific to the first receptor can then be used. Detection of the complex can be effected after washing using known techniques. Further details of how direct binding assays are carried out are provided for example in US-A-4,497,899 and EP-A 0 439 211. Examples of other useful assays include competitive immunoassays and enzyme-linked immunosorbent assays. A preferred embodiment of this invention is an immunometric or sandwich assay in which the extracted ligand is reacted at different epitopic sites with two receptor molecules, one of which is labeled with peroxidase, and the second being immobilized (or capable of being immobilized such as through avidin-biotin complexation). Suitable materials on which one receptor is immobilized include, but are not limited to, particulate carrier materials formed from organisms, natural or synthetic polymers, glass, ceramics, diatomaceous earth or magnetizable particles, microtiter plates, glass slides or tubes, membranes, polymeric or cellulosic papers or films. Preferably, particulate materials are used. These particles are more preferably polymeric, spherical in shape and have an average particle size (in largest dimension) of from 0.01 to 10 µmeters. The insolubilizable receptors used in the immunometric assays can be attached to water-insoluble materials by physical or chemical means, including adsorption or covalent reaction with reactive groups on the surface of the materials. Covalent attachment is preferred for better assay sensitivity. Many useful reactive groups are known in the art, which groups can be part of the chemical structure of the carrier material, or added by coating or chemical treatment of an inert material. Particularly useful particulate materials are polymeric beads which are described, for example, in EP-A-0 323 692 and which are prepared from one or more ethylenically unsaturated polymerizable monomers having an active halo atom, activated 2-substituted ethylsulfonyl or vinylsulfonyl groups. Other particularly useful particles having reactive carboxy groups are described in EP-A-0 466 220. Homo- and copolymers described in EP-A-0 323 692 include the following representative materials: poly( m & p -chloromethylstyrene), poly(styrene- co - m & p -chloromethylstyrene- co -2-hydroxyethyl acrylate) (67:30:3 molar ratio), poly[styrene- co - m & p -(2-chloroethylsulfonylmethyl)styrene] (96:4 molar ratio), poly(styrene- co -N-[ m & p -(2-chloroethylsulfonylmethyl)phenyl]acrylamide) (99.3:0.7 molar ratio), poly( m & p -chloromethylstyrene- co -metharylic acid) (95:5 molar ratio), poly[styrene- co - m & p -(2-chloroethylsulfonylmethyl)styrene- co -methacrylic acid] (93.5:4.5:2 molar ratio) and poly[styrene- co -4-(2-chloroethylsulfonylmethyl)styrene] (95.4:4.5 molar ratio). Procedures for attaching antibodies or other biological materials to particles having reactive groups are well known. In general, the receptors are mixed with the particles under suitable conditions depending upon the attachment form (adsorption, covalent reaction directly or by use of a linking group). A worker skilled in the art would readily know what conditions should be used for each procedure. For example, for attachment to particles having reactive halo atoms, activated 2-substituted ethylsulfonyl or vinylsulfonyl groups, the receptors are generally mixed with the particles for up to 24 hours at a temperature of from 20° to 40°C in a suspension buffered at a pH of from 7 to 10. If carboxy groups are used for attachment, the well known carbodiimide activators can be used, as well as carbomoylonium compounds which are described in EP-A-0 308 235. Receptors can be absorbed on particles by incubating them with particles in suspension at suitable temperature for several hours. More preferably, the insolubilized receptors described above are coated or deposited on a microporous filtration membrane which is inert to chemical or biological reactions. It is generally composed of one or more natural or synthetic substances which have sufficient integrity for reagents to react or be affixed thereto without loss of form or function. It is porous enough for filtration needed to remove substantially all uncomplexed materials from the complexes formed thereon. Useful membrane materials include porous natural or synthetic polymers, sintered glass, membranes of glass or polymeric films or fibers, ceramic materials, cellulosic materials and particulate structures composed of beads bound together with an adhesive or binder material. Particularly useful materials are treated or untreated polyamide microporous membranes such as those commercially available from Pall Corp. under the trademarks LOPRODYNE™ and BIODYNE™. The membrane generally has an average pore size in the largest dimension of from 0.5 to 5 µmeters. The water-insoluble receptors can be affixed to the membrane over its entire surface or in defined regions thereof. They can be used in admixture with hydrophilic binders to provide additional integrity to the coating. The membrane can be hand held in the assay to provide sites for complexation of extracted ligand and receptor thereon. However, preferably, the membrane is disposed or mounted in a disposable test device or article having a suitable frame and structure for holding the membrane and fluid which is drained therethrough. Many such test devices are known in the art. Particularly useful test devices are those marketed by Eastman Kodak Company under the trademark SURECELL™ test devices. Preferred test devices have three test wells designed for providing both negative and positive control results as well as a specimen test result. Each test well has a membrane situated therein. As noted above, the receptor can also be designed for being insolubilized using a specific binding complex such as avidin-biotin, a sugar with a lectin or others known in the art. The receptor molecule to be insolubilized can be biotinylated (such as a biotinylated antibody or nucleic acid ), and before, during or after its reaction with the ligand, it can be complexed with avidin which is attached to a solid material. Once the insolubilized complex has been formed, the next step (step C) of the method of this invention is to contact it with a composition suitable for providing a colorimetric or chemiluminescent signal in response to the peroxidase label in the complex. Such a composition can merely be a substrate for peroxidase which is reacted upon to provide the desired signal. More likely, it is two or more reagents which function in one or more reactions to provide the signal. The particular reagents needed would be readily apparent to one skilled in the art since there is considerable art describing reagents which are catalyzed by peroxidase to form dye or chemiluminescent signals. Generally, the composition includes hydrogen peroxide and a compound which provides a signal in response thereto. For example, a number of leuco dyes are known to be useful for this purpose including those described in US-A-4,089,747 and US-A-4,670,386. A preferred dye-providing composition is illustrated in the examples below. Alternatively, the peroxidase can be used in one or more reactions to produce a chemiluminescent signal. The advantage of the present invention is effective modulation (changing or stopping completely) of the signal produced using the composition of the hydroxamic acid described above. This is done by contacting the complex producing the signal with the composition at a suitable time after signal production has begun. Generally, this contact occurs within at least 2 minutes after dye signal begins, and preferably after from 60 to 75 seconds. At this point, a dye signal exists but its intensity stops increasing. For a chemiluminescent signal, the composition stops the production of light from the complex. The method of this invention can be carried out over any suitable period of time with at least 3 minutes being the minimal time necessary. Generally, the assay (steps A-D) is carried out in from 3 to 60 minutes. Except for temperature conditions noted above for individual steps, generally the assay is carried out at from 15 to 40°C with room temperature being preferred. The method may include a number of optional steps not specifically enumerated in the generic procedure including, but not limited to wash steps, extraction steps, filtration steps and others known to one skilled in the art of immunoassays or hybridization assays. In a preferred embodiment, a method for the determination of any of Actinobacillus actinomycetemcomitans , Prophyromonas gingivalis or Prevotella intermedia comprises: A. contacting a specimen suspected of containing an antigen extracted from any of Actinobacillus actinomycetemcomitans , Porphyromonas gingivalis or Prevotella intermedia with a water soluble antibody specific for the extracted antigen, the antibody being labeled with peroxidase, to form a peroxidase-labeled immunological complex between the extracted antigen and antibody, B. prior to, simultaneously with or subsequently to step A, insolubilizing the extracted antigen so as to provide an insolubilized immunological complex, C. contacting the insolubilized complex with a composition for providing a colorimetric or chemiluminescent signal in response to peroxidase in the complex, and D. modulating and detecting the level of the signal by contacting the insolubilized complex with a composition comprising at least 0.05 to 5 weight percent of a compound as described above. The following examples are included to illustrate the practice of this invention, and are not meant to be limiting in any way. All percentages are by weight unless otherwise noted. Materials and Methods for Examples : SURECELL™ disposable test devices were used containing LOPRODYNE™ nylon microporous filtration membranes (1.2 µmeters average pore size) incorporated into the three test wells. The membrane was used without any further treatment. A dye-providing composition was prepared to include 4,5-bis(4-methoxyphenyl)-2-(3,5-dimethoxy-4-hydroxyphenyl)imidazole leuco dye (0.008%), poly(vinyl pyrrolidone) (1%), sodium phosphate buffer (10 mmolar, pH 6.8), hydrogen peroxide (10 mmolar), 4'-hydroxyacetanilide (5 mmolar) and diethylenetriaminepentaacetic acid (10 µmolar). Polyclonal antibodies directed against each of the three microorganisms Actinobacillus actinomycetemcomitans ( A.a. ), Prevotella intermedia ( P.i. ) and Porphyronomas gingivalis ( P.g. ) were prepared by intravenous injection of rabbits. This procedure generally included injecting the rabbits with an immunizing amount of antigen a first time, injecting the animals a second time between the second and fourteenth days after the first injection with a boosting amount of the antigen. Beginning the fifteenth day after the first injection, the rabbits were injected at least three times every seven day period for at least four seven-day periods with a boosting amount of antigen. After the last booster injection, antisera was removed from the rabbits. IgG fractions were prepared by ammonium sulfate precipitation, and stored at 4°C in phosphate buffered saline solution (0.3-0.4% solution). Isolates were subcultured on anaerobic plates. The microorganisms were those identified by the deposit numbers of ATCC 43717, ATCC 43718 and ATCC 43719 for A.a. (serotypes A, B and C), ATCC 25611, NCTC 9336 and ATCC 49046 for P.i. (serotypes A, B and C) and ATCC 33277, 53978 and 53977 for P.g. (serotypes A, B and C). Water insoluble reagents were prepared by covalently binding antibodies specific to each microorganism (all of serotypes A, B and C) to polymeric particles (1 µmeter average diameter) of poly[styrene- co -4-(2-chloroethylsulfonylmethyl)styrene] (95.5:4.5 molar ratio) which had been prepared using the procedures of EP-A-0 323 692. Covalent attachment was achieved by adding the antibodies (0.75 mg/ml for P.g. , total serotypes, and 0.52 mg/ml for A.a. and P.i. , total serotypes) to a solution of borate buffer (0.05 molar, pH 8.5) in a test tube and mixing well. The polymeric particles (3% solids) were added to the buffered mixture, and the resulting suspension was rotated end-over-end for 4-24 hours at room temperature to allow covalent attachment of the antibodies to the particles. The suspension was then centrifuged at 2800 rpm for 10 minutes. The supernatant was discarded and the pellet was suspended in glycine buffer (0.1%, pH 8.5) containing merthiolate (0.01%). A coating suspension of the reagent described above (0.35% solids) was prepared to have polyacyrylamide binder (5%), TWEEN™ 20 nonionic surfactant (0.1%), merthiolate (0.01%) and UVITEX™ optical brightener (0.0005%, Ciba-Geigy) in glycine buffer (0.1 molar, pH 8.5). Each reagent directed to a distinct antigen was coated in defined regions of the membrane in the test devices described above. Enzyme-antibody conjugates were prepared using antibodies directed to each microorganism conjugated to horseradish peroxidase using the procedure of Yoshitake et al, Eur.J.Biochem. , 101 , 395, 1979. Each conjugate composition comprised the conjugates (5.6-11.25 µg of each per ml) added to a solution of casein [0.05%, from a 1% solution in 0.05 molar phosphate buffered saline solution, pH 7], TWEEN™ 20 nonionic surfactant (0.3%), merthiolate (0.01%), 4'-hydroxyacetanilide (10 mmolar) and LONZAINE™ C amphoteric surfactant (0.0035%, Lonza Corp.). The amount of antibody specific for A.a. (all serotypes) and P.g. (all serotypes) was 7.5 µg/ml. For P.i. (serotypes A and C), the amount was 5.6 µg/ml, and for serotype B it was 11.25 µg/ml. The wash solution used comprised TERGITOL™ 4 anionic surfactant (1.35%) in glycine buffer (0.1 molar, pH 10) containing casein (0.5%) and merthiolate (0.01%). Ahtigen extraction was accomplished using a solution of EMCOL ™ CC-9 cationic surfactant (5%, Witco Chemical Co.), sodium dodecyl sulfate (5%) in glycine buffer (0.1 molar, pH 8.5). Example 1 Use of Various Compositions to Modulate or Stop Dye Signal This example demonstrates the practice of this invention and the use of a benzohydroxamic acid to modulate the formation of a dye signal using a peroxidase-labeled antibody. Extraction and Assay Protocol: Antigen extraction was accomplished by mixing the microorganism specimen with the extraction solution noted above (450 µl) for about 1 minute at room temperature. The amount of cells in the final solutions was 7 x 10 5 cells/ml of P.g. The assays were carried out by adding a sample (450 µl) of extractant provided by the extraction procedure noted above to each test well of the disposable test device as described above. Fluid was allowed to drain through the membranes in the test wells as the extracted antigen complexed with the immunological reagent (containing antibodies) on the membranes. Immediately, the conjugate of peroxidase and antibody (80 µl) was added to the test wells and sandwich complex formation was allowed to proceed by incubation at room temperature for about 2 minutes. Each test well was then half filled with the wash solution (about 500 µl) which then drained through the membrane. This was repeated once. After the last wash, the dye-providing composition (120 µl) was added to each test well followed by a 1 minute incubation at room temperature. At the end of this incubation period, the "stop" solution was added to modulate the formation of dye signal, and the signal was visually evaluated by comparing it to a color score card having density values of 1 to 10 with 10 representing the highest density. A density score was also given to the background on the membrane where no dye should appear. The "stop" solutions evaluated were as follows: Control A: sodium azide (0.1%) in phosphate buffered saline solution (0.05 molar, pH 7.3). Control B: sodium azide (0.1%) in 3-(4-morpholino)propanesulfonic acid (1 molar, pH 7). Control C: sodium azide (0.1%) in 2-(4-morpholino)ethanesulfonic acid (1 molar, pH 6). Control D: sodium azide (1%) in 3-(4-morpholino)propanesulfonic acid (1 molar, pH 7). Control E: sodium azide (1%) in 2-(4-morpholino)ethanesulfonic acid (1 molar, pH 6). Control F: citric acid (1 molar, pH 4). Control G: citric acid (1 molar, pH 3). Control H: citric acid (1 molar, pH 2). Control I: ethanolamine (1 molar, pH 10). Control J: ethanolamine (1 molar, pH 11). Control K: sodium azide (0.1%), poly(vinylpyrrolidone) (6.25%) and TERGITOL™ 4 anionic surfactant (0.1%) in 2-(4-morpholino)ethanesulfonic acid (1 molar, pH 6). Example 1: benzohydroxamic acid (0.1%) in phosphate buffered saline solution (0.05 molar, pH 7.3). Table I below shows the time (minutes) after the addition of "stop" solution at which dye development due to non-specific binding was observed. This is undesirable binding of the labeled antibody in the region of the membrane removed from the complex. It can be seen that the "stop" solution containing the benzohydroxamic acid according to this invention provided the longest time before a dye signal from non-specific binding was observable. "Stop" Solution Time (Minutes) Control A 4-5 Control B 4-5 Control C 6 Control D 7 Control E 15 Control F 4-5 Control G 7 Control H 45 Control I 10 Control J 10-15 Control K 6-10 Example 1 >60 Table II below quantitates the area of the membrane affected by non-specific binding after the formation of dye signal after certain periods of time. The values of "1+" to "4+" refer to the intensity and size in area of development of dye signal on the membrane with a value of 1+ referring to a small portion of the membrane being affected with low dye signal, and a value of 4+ referring to the entire membrane having a very high dye signal. These data indicate that only the present invention consistently provided no undesired dye signal over the entire period of the test (1 hour). Table III below shows the dye signal generated in response to the presence of P.g. (serotype B, 7 x 10 5 cells/ml) after certain times for certain "stop" solutions. The assay carried out according to this invention provided the most stable dye signal after 15 minutes. The dye signals were evaluated on a scale of 1 to 10 with 10 representing the highest dye density. Time (Min.) "Stop" Solutions Control A Control E Control G Control H Control J Control K Example 1 0 5 5 5 5 5 5 5 5 5 5 5 4-5 2-3 5 5 10 U 5 4-5 3 U 5 5 15 U 4 4 1 U U 5 U = unable to evaluate In summary, the data indicate that the use of benzohydroxamic acid to modulate or stop the formation of dye signal according to this invention is quite successful. Not only is the dye signal stabilized over a long period of time, but it unexpectedly eliminates the background signal caused by the backflow of reagents through the membrane on which the signal is generated. This allows the user of this assay sufficient time to evaluate the dye signal and provides for semi-quantitative results since there is less background and a more stable signal.

Claims: A diagnostic test kit comprising a water soluble, peroxidase-labeled specific binding species, the kit characterized as further comprising, separately packaged, a buffered composition comprising at least 0.05 weight percent of a compound having the structure R-CO-NH-R' or an equivalent salt thereof, wherein R is phenyl, alkyl having 1 to 4 carbon atoms or cycloalkyl having 5 or 6 carbon atoms in the ring, and R' is hydroxy. The kit as claimed in claim 1 further comprising a composition for providing a colorimetric or chemiluminescent signal in response to peroxidase. The kit as claimed in either of claims 1 and 2 wherein the specific binding species is an antibody which is specific for Actinobacillus actinomycetemcomitans , Porphyromonas gingivalis or Prevotella intermedia . A method for the determination of a specific binding ligand comprising: A. reacting a specific binding ligand from a biological specimen with a water soluble receptor specific for said ligand, the receptor being labeled with peroxidase, to form a peroxidase-labeled specific binding complex between the ligand and receptor, B. prior to, simultaneously with or subsequently to step A, insolubilizing the specific binding ligand so as to provide an insolubilized specific binding complex, C. contacting the insolubilized complex with a composition for providing a colorimetric or chemiluminescent signal in response to peroxidase in the complex, and D. modulating and detecting the level of the signal by contacting the insolubilized complex with a composition comprising at least 0.05 weight percent of a compound having the structure R-CO-NH-R' or an equivalent salt thereof, wherein R is phenyl, alkyl having 1 to 4 carbon atoms or cycloalkyl having 5 or 6 carbon atoms in the ring, and R' is hydroxy. The method as claimed in claim 4 for the determination of a hormone, drug, bacterial or viral antigen or an antibody. The method as claimed in claim 4 for the determination of Actinobacillus actinomycetemcomitans , Porphyromonas gingivalis or Prevotella intermedius . The method as claimed in any of claims 4 to 6 wherein the complex is insolubilized on a microporous filtration membrane, and step D is carried out within 2 minutes after step C. The kit or method as claimed in any of the preceding claims wherein the compound is present in an amount of from 0.05 to 5 weight percent. The kit or method as claimed in any of the preceding claims wherein the peroxidase is horseradish peroxidase.

Inventors: BOYER BRADLEY PORTER, CONTESTABLE PAUL BERNARD, KISSEL THOMAS ROBERT, SNYDER BRIAN ANTHONY, BOYER, BRADLEY PORTER, CONTESTABLE, PAUL BERNARD, KISSEL, THOMAS ROBERT, SNYDER, BRIAN ANTHONY, BOYER, BRADLEY PORTER, C/O EASTMAN KODAK CO., CONTESTABLE, PAUL BERNARD, C/O EASTMAN KODAK CO., Kissel, Thomas Robert, c/o Eastman Kodak Co., SNYDER, BRIAN ANTHONY, C/O EASTMAN KODAK CO.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1992
Main classification: G01N33
IPC codes: G01N33, C12Q1