Abstract: The present invention provides specific binding solid phase assay methods and kits for the detection of the presence or absence of a microorganism by directly staining the microorganism and specifically capturing the stained microorganism on a solid support. The methods find particular utility in the detection of Candida. The methods may simultaneously detect the presence or absence of multiple microorganisms.

Abstract: This invention relates to a lateral flow immunochromatographic assay device without a plastic housing. The assay includes a sample receiving region, analyte detection region and end region all made of porous material and capable of lateral flow. The analyte detection region includes labeling reagents, a capture reagent and a control reagent. The back of the porous material is laminated with a semi-rigid material with adequate mechanical strength. The top is partially covered with a thin plastic material so as to leave a portion of the sample receiving region exposed for sample application.

Abstract: A test strip for a rapid immunoassay containing specific immunochemical reagent zones (7, 8, 9) is described. The test strip (10) has a backing sheet (1) and attached thereto a receiving end pad (3) and at a distance therefrom a finishing end pad (5). A test membrane (2) is provided between said pads (3, 5). Said membrane (2) is positioned in parallel relationship to said backing (1) at a distance therefrom so that said backing (1) and said membrane (2) limit between themselves an air gap (4) which is open at its edges. Said gap (4) functions as a sheltered reaction chamber for the immunolgical reaction taking place as a liquid is made to flow through said membrane (2). The test strip is simple to manufacture by lamination and easy to use and it is suitable for both diagnostic and environmental immunoassays.

Abstract: A carboxyterminal propeptide of type I procollagen free from type III procollagen carboxyterminal propeptide can be used to produce an antibody which is specific for carboxyterminal propeptide of type I procollagen and which has no affinity for the type III procollagen carboxyterminal propeptide. This antibody can be used to assay more accurately the propeptide which is a measure of the rate of production of type I procollagen and useful in diagnosing and monitoring e.g. bone diseases.

Abstract: The present invention is drawn to an immunoassay capable of the rapid detection of a variety of test substances that may be present in a test sample. One feature of the invention is that extraction or isolation of the test substance occurs simultaneously with the formation of the primary antigen-test substance complex. The primary antigen-test substance complex is then captured in a solid phase format having a plurality of interstitial spaces which facilitate rapid and efficient detection. The immunoassay of the present invention works over a wide range of environmental conditions and is simple enough to be used in the absence of laboratory facilities.

Abstract: This invention presents novel assay devices employing capture reagents, involving a specific binding member attached to a charged substance, and porous material containing a capture or reaction zone that is oppositely charged with respect to the charged substance included in the capture reagent. In one embodiment, a test sample suspected of containing the analyte of interest is contacted with the capture reagent to form a charged capture reagent/analyte complex. The complex is then contacted to the oppositely charged capture or reaction zone to attract, attach, and immobilize the capture reagent/analyte complex. With an appropriate indicator reagent, both sandwich and competitive assays can be performed.

Abstract: The invention relates to a method of using a pair of leucine zipper peptides for in vitro diagnosis, in particular, for the immunochemical detection and determination of an analyte in a biological liquid. In one method, the first leucine zipper peptide is immobilized by attaching it to a solid support, the second leucine zipper peptide is coupled to a specific binding partner for the analyte, the two peptides are brought into contact, the sample of the biological liquid is brought into contact with the immobilized first peptide and the specific binding partner for the analyte, and the amount of analyte bound to the binding partner is determined. The leucine zipper peptides are preferably v-fos and c-jun.

Abstract: A method is described for determining a hapten which method comprises (i) contacting the hapten with a binding partner of the hapten, whereby the hapten becomes bound to some of the binding partner, (ii) contacting the unbound binding partner with a secondary binding partner therefor, (iii) contacting the binding partner with an antibody which binds the binding partner which has bound thereto the hapten but which does not bind the binding partner which has bound thereto its secondary binding partner; and (iv) determining the amount of antibody bound to the binding partner. Kits for use in the method are also described.

Abstract: A method is revealed for the quantitative determination of the proportion of the free form of a thyroid hormone ligand in a sample of a biological fluid in which the ligand is present partly in the free form and also partly in a form in which it is bound to physiological binding proteins. In the first step, a ligand derivative of the thyroid hormone with an immunoglobulin, a labelled specific binder, and a test tube whose walls are coated with an excess of a protein material are provided. In the second step, a sample of the biological fluid containing an unknown amount of the free thyroid hormone ligand, a solution containing a known amount of the ligand derivative, and a solution containing a known, less than stoichiometric amount of the labelled specific binder are added to the test tube to form a liquid reaction mixture.

Abstract: The present invention relates to a process for determining complexes of .alpha.-1-antichymotrypsin and cathepsin G in a sample comprising adsorbing the cathepsin G portion of the complex to a solid phase coated with non-specific binding protein or gelatin, and detecting the .alpha.-1 portion of the complex with a detectably labelled anti-.alpha.-1-antichymotrypsin antibody. A diagnostic kit comprising the solid phase coated with non-specific binding protein or gelatin and the labelled anti-.alpha.-1-antichymotrypsin antibody is also provided.

Abstract: An analytical test device useful for example in pregnancy testing, includes a hollow casing (500) constructed of moisture-impervious solid material, such as plastics materials, containing a dry porous carrier (510) which communicates indirectly with the exterior of the casing via a bibulous sample receiving member (506) which protrudes from the casing such that a liquid test sample can be applied to the receiving member and permeate therefrom to the porous carrier, the carrier containing in a first zone a labelled specific binding reagent is freely mobile within the porous carrier when in the moist state, and in a second zone spatially distinct from the first zone unlabelled specific binding reagent for the same analyte which unlabelled reagent is permanently immobilised on the carrier material and is therefore not mobile in the moist state, the two zones being arranged such that liquid sample applied to the porous carrier can permeate via the first zone into the second zone, and the device incorporating an a

Abstract: An immunoassay process is provided for the detection of a target antigen in a fluid sample where an admixture of the target antigen and a labeled capture reagent against the target antigen is contacted by a solid polymeric carrier having bound to a portion of its surface a capture reagent against the target antigen and visual determination of a change in color of the bound labeled reaction product on the surface of the solid carrier member serves to readily detect the presence of the target antigen.

Abstract: The binding site on an immunoglobulin for a protein is blocked by hydrophobically coupling the immunoglobulin to a blocking agent such as a label. This results in a detection reagent useful in a variety of test assays in which a protein and an immunoglobulin are advantageously used together, but separately. The reagent is useful in the simultaneous determination of IgG and one of IgA or IgM. Anti-IgA-IgG or anti-IgM-IgG is coupled to a hydrophobic label, particularly a pigment or dye, which label blocks the binding site on IgG for Protein A, and labeled Protein A is added.

Abstract: This invention pertains to methods to detect antibodies in a sample. The methods use an amount of antigen that is up to 1000, preferably 10-100 times the minimum amount antigen that can be reliably detected and that is less than the maximum expected amount of antibodies in the sample. An antigen:antibody complex is formed and becomes bound to a binding agent that does not bind free antigen. The free antigen is then detected as a measure of antibodies present in the sample.

Abstract: An assay and method for screening newborns to determine risk of Sudden Infant Syndrome is described. The assay and method is based on the detection of elevated IgM-anti-IgG (MAG) levels in newborns' serum within the first year of birth. In particular, it has been discovered that elevated MAG levels indicate an increased risk of Sudden Infant Death Syndrome (SIDS).In a preferred embodiment of the invention, an ELISA is utilized in which a first binding agent having specific affinity for IgM is used to capture and separate IgM antibodies from the newborn's blood sample. A second binding agent having specific affinity for IgG which has been separated from the sample eluant by complexing with MAG, is then used in conjunction with an enzyme conjugate to indirectly determine the amount of MAG in the newborn's blood. The MAG level is then compared to a cut-off which is selected to separate out approximately 4% of the newborns which have the highest MAG levels.

Abstract: The amount of an analyte in a sample derived from a living sample is measured by reacting the analyte with an excess of a substance having affinity for the analyte, followed by separation of complex by high pressure liquid chromatography and measurement using a linear calibration curve representing the peak area values associated with known concentrations of analyte.

Abstract: An antibody raised to type I collagen carboxyterminal cross-linked telopeptide isolated from decalcified human or animal bone, may be used in an assay to determine the concentration of liberated carboxyterminal telopeptide region of the type I collagen molecule in a sample. When the sample is a body fluid such as serum or urine the degradation product measured is resistant to further degradation, since it contains a multivalent intermolecular cross-link, and can thus be found in the body fluid. The assay may be used to assess the degradation of type I collagen, the major organic constituent of bone matrix.

Abstract: An apparatus for magnetic cell separation using paramagnetic microbeads includes a base upon which is movably carried a rocker member. The rocker member carries both a primary processing container in which a mixture of liquid with cells and paramagnetic microbeads is received; and a primary magnet movable from a first position adjacent to the primary container to magnetically capture the microbeads, and a second position spaced from the primary container to magnetically release the microbeads. The mixture of liquid with cells and microbeads is agitated by tilting motions of the rocker assembly, thereby achieving the binding of target cells to microbeads. The paramagnetic microbeads, with bound target cells, are captured and released by movements of the primary magnet between its first and second positions. A secondary magnet is placed downstream from the primary magnet to capture any paramagnetic microbeads which might escape from the primary magnet.

Abstract: Assay reagents, devices, methods and kits used in the analysis of low molecular weight analytes which by themselves are too small or unable to bind to two specific binding members at the same time. The invention involves the use of an analyte-substitute reagent (ASR) comprising at least two components, the first of which is identical to or an analog of the analyte to be determined, while the second is an unrelated ligand for which an antibody or other specific binding member can be obtained or produced.

Abstract: A device for collecting a specimen, including (a) a test vessel for containing a solution containing an immunocomplex, which is a complex as a result of an antigen-antibody reaction between a specimen and a magnetic-labeled antibody containing a magnetic micro-particle and an antibody fixed to the micro-particle, (b) an external magnetic field generating device for generating a magnetic field, preferably a gradient magnetic field and applying it to the solution in the test vessel to effect local concentration of the immunocomplex to a predetermined position, (c) a magnetic member for collecting the immunocomplex at the position of local concentration, and (d) a moving mechanism for achieving relative movement between the magnetic member and the test vessel.

Abstract: Methods and test devices for detecting the presence or amount of target ligand in non-competitive sandwich ligand-receptor assay processes. Antibodies which bind to the complex of ligand receptor and target ligand but do not bind significantly to the ligand receptor and which bind the target ligand with substantially less affinity than the complex are taught and their uses described. These assays can be used to eliminate the "hook" effect in non-competitive sandwich assays. Furthermore, the antibodies are selected and assay methods described so that, as a result of the assay process, no detectable response is observed due to the binding of antibody and ligand receptor in the absence of target ligand.

Abstract: A method is described for determining a hapten which method comprises (i) contacting the hapten with a binding partner of the hapten, whereby the hapten becomes bound to some of the binding partner, (ii) contacting the unbound binding partner with a secondary binding partner therefor, (iii) contacting the binding partner with an antibody which binds the binding partner which has bound thereto the hapten but which does not bind the binding partner which has bound thereto its secondary binding partner; and (iv) determining the amount of antibody bound to the binding partner. Kits for use in the method are also described.

Abstract: A magnetic separator for isolating magnetically-labeled substances of interest, such as immunological agents, from a non-magnetic test medium using a method of high gradient magnetic separation. The target substance is contacted with microscopic magnetic particles having a receptor for binding with the target substance. The test medium containing the magnetic particles is held in a non-magnetic container and placed into a gap within an arrangement of magnets for causing the magnetic particles to adhere to selected locations upon the interior wall of the container. The quantity of magnetic particles may be controlled to cause the magnetic particles collected upon the interior wall to form a monolayer. The magnets are arranged upon a yoke which may provide linear, surrounding multipolar, or partially surrounding multipolar configurations of magnetic pole faces about the gap.

Abstract: An antigen capture method, and an antigen capture assay diagnostic kit, for detecting the presence or concentration of HIV in a biological sample without interference from antigen-antibody immune complexes is provided. The lysate of a biological sample obtained from an animal is contacted with a detectable amount of an antibody specifically reactive with the nucleocapsid p7 antigen or an immunoreactive fragment of the p7 antigen for a time and under conditions sufficient for p7 antigen contained in the lysate to form a p7-antibody complex. The presence or concentration of this p7-antibody complex is determined to detect or quantitate the presence of HIV in the biological sample. Uses of this assay and method include detecting the presence of HIV infection in an infant born to an HIV-infected mother, monitoring the progression of HIV infection, and evaluating the effectiveness of an anti-HIV treatment administered to an animal, such as a human.

Abstract: A patient's health is diagnosed by centrifuging blood samples in a transparent tube, which tube contains one or more groups of particles such as lyposomes or plastic beads of different densities for each group. Each group of density-defined particles carries antigens or antibodies which are specific to a complement antigen or antibody which may be in the blood sample being tested, and which are indicative of the patient's health. A label-tagged antibody which is specific to all bound antibody/antigen couples is added to the blood sample so as to form labelled antibody+antigen-antibody complexes (AAAC) in the blood sample. Upon centrifugation, the complexed particles will settle out in different areas in the tube according to the respective density of the particles, and the degree of label emission of the particle layers can enable qualitative or quantitative analyses of the blood sample to be made.

Abstract: The present invention includes novel digoxin assays employing a capture reagent, involving a first binding member conjugated to a polymeric anion substance, and a solid phase material containing a reaction site comprising a polymeric cation substance having a nitrogen content of at least about two percent. A test sample suspected of containing the analyte of interest may be contacted with the capture reagent to form a charged capture reagent/analyte complex. The complex is then contacted to the oppositely charged solid phase to attract, attach, and immobilize the capture reagent/analyte complex.

Abstract: An assay provides for detecting the presence of an analyte in a sample. Sample is applied to move through three zones. A mobilizeable receptor capable of binding to the analyte is present in the first zone. A trap for unbound receptor, consisting of immobilized ligand, is present in the second zone. Receptor bound to analyte will not bind to the ligand; unbound receptor will bind to the ligand. Mobilization and migration of the receptor can be detected in the third zone, which positively indicates that analyte is present. A device for carrying out the method is also provided.

Abstract: An improved method for performing immunoassays whereby specific binding proteins for vitamin B12, folate and other target analytes are utilized with antibodies with different specificities for the binding proteins. Antibodies bridge the specific binding protein directly or indirectly to a capturable material.

Abstract: The present invention relates generally to test articles and assays for the detection of analytes in biological fluid samples. More particularly, the present invention relates to test articles an assays which employ dyed microorganisms as visual labels to detect suspected analytes.

Abstract: The present invention is related generally to methods and compositions for identifying and quantitating particular .alpha.1-antichymotrypsin species in a biological sample. More particularly, the present invention is related to methods and compositions for detecting and measuring a brain .alpha.1-antichymotrypsin species that is produced in brain tissue of individuals having a neuropathological condition and which is detectable in accessible biological samples. The invention provides detection assays, such as sandwich binding assays, for detecting and quantitating brain .alpha.1-antichymotrypsin in a biological sample, such as blood, urine, cerebrospinal fluid, or tissue. These detection assays are useful for detecting and diagnosing neuropathological diseases and for identifying cells of a human central nervous system lineage, and for other medical applications. The invention also provides binding components, such as antibodies that bind to brain .alpha.

Abstract: The present invention relates to a process of preparing a sandwich immunoassay of NAG, which comprises (1) reacting NAG with an immobilized anti-NAG monoclonal antibody and a labeled anti-NAG monoclonal antibody to form a complex of immobilized antibody-NAG-labeled antibody and (2) detecting the activity of said reacted and unreacted labeled anti-NAG antibody.This sandwich immunoassay is useful for diagnosis of renal disease, hepatitis, leukemia, and other such diseases. It also allows the direct and specific detection of NAG isozymes B and I in urine and blood.

Abstract: Assay reagents, devices, methods and kits used in the analysis of low molecular weight analytes which by themselves are too small or unable to bind to two specific binding members at the same time. The invention involves the use of an analyte-substitute reagent (ASR) comprising at least two components, the first of which is identical to or an analog of the analyte to be determined, while the second is an unrelated ligand for which an antibody or other specific binding member can be obtained or produced.

Abstract: This invention relates to methods that have been found useful in reducing non-specific binding in immunochemical assays, via methods that can be implemented much faster than those used by Ishikawa. The techniques include the use of a lipophilic bridge, such as a liposome, or the elution of the antigen-antibody complex from the solid phase by the use of an anti-idiotypic antibody or an antibody, or the use of a heterologous reversible bridge.

Abstract: Methods for purifying and detecting IgM antibodies employ binding substances which are Borellia burgdorferi cells, or cellular or extracellular components obtained or derived therefrom and which bind to this class of antibodies. The binding substances may be attached to a solid substrate and then the substrate contacted with a solution containing IgM antibodies under conditions such that the antibodies bind to the binding substance on the substrate. The substrate is then contacted with a solution that releases the IgM antibodies from the substrate and the antibodies are recovered or detected. Applications of these methods include, for example, assays for diagnosing diseases which elicit primary and/or secondary IgM antibody-mediated immunity.

Abstract: Disclosed is a novel immunoassay methodology, bridge immunoassay, which employs a primary free solution analyte/receptor binding reaction, for example, in a sandwich-type format (two or more analyte receptors), in a competitive format (single analyte receptor) or in a related immunoassay format, and a universal solid phase and capture system. The universal capture system comprises a first receptor bound to a solid phase and a bridge receptor (a second receptor) which functions both as a ligand for said bound first receptor and as a receptor for a ligand conjugated to a sample analyte receptor (a third receptor). The bridge receptor is used to immobilize the immunocomplexes formed free in solution by linking them to the bound first receptor. The universal capture system can be used for assays for any analyte as the bridge receptor binds to a ligand, for example, a hapten or binding protein, conjugated to the sample analyte receptor. Methods, compositions and test kits for such bridge immunoassays are provided.

Abstract: A macroglobulin is used to improve the signal-to-background ratio in an affinity binding assay employing a proteinase (or precursor) as a label. The macroglobulin entraps unbound labeled reagent, thereby reducing its signal generating activity, relative to that of the affinity complex.

Abstract: A method disclosed for studying the interaction in solution of two molecules of the type such as a ligand and a receptor that are capable of reacting or binding with each other. The method comprises preparing an aliquot of a solution containing the first of the molecules. The second of the molecules is then added to the aliquot. A fluorescently labeled molecule is added to the aliquot, wherein the fluorescently labeled molecule is also capable of reacting or binding with the second of the molecules. A porous matrix that is optically transparent is immersed into the aliquot containing the two molecules being studied and the fluorescently labeled molecule, wherein the second molecule and any fluorescently labeled molecule bound thereto is sterically hindered from permeating the porous, optically transparent matrix, while any unbound fluorescently labeled molecule permeates the matrix.

Abstract: A device for the rapid qualitative and quantitative determination of the presence of a reactive ligand in a fluid.This device comprises a first reaction zone in which there is an at least temporarily impermeable membrane designed to receive a sample of test fluid and to be associated with at least one labeled reagent; a second reaction zone which is bounded on the one hand by the said membrane and on the other by a second at least temporarily impermeable membrane comprising a solid phase containing a reference reagent; and a third reaction zone which contains means for developing the reaction.A method for the rapid qualitative and quantitative determination of the presence of a reactive ligand in a fluid.Applications to the detection of the presence, in a biological fluid, of antibodies or antigens in particular.

Abstract: Methods for determining the presence and/or concentration of an analyte in a biological fluid sample are disclosed. The methods generally include admixing in solution certain polymer/reactant and reporter/reactant conjugates along with the biological fluid sample suspected of containing the analyte, thereby forming ternary complexes. The separation of the complexes from the reaction mixture is achieved through the affinity of certain selected polymer compositions for various solid phases. Upon separation, the amount of reporter activity in the solution may be measured, and therefrom the presence and/or concentration of the analyte determined. Multiple analyses on a biological fluid sample suspected of containing one or more analytes may also be performed, using either a variety of different reporters or selected polymers having varied affinity for the solid phase.

Abstract: Rapid assays for analytes of interest in a fluid sample utilize a first conjugate of a labelled reactant that specifically binds to the analyte, and a second conjugate that binds to the analyte coupled to a polymer that has an affinity for a selected solid phase. The reaction components are incubated briefly, then contacted with the selected solid phase and the labelled components determined. Optional wash steps provide for enhanced sensitivity and specificity. When the analyte of interest is an antibody to HIV, the first reactant may be a synthetic, recombinant or native HIV antigen, and the second reactant may be protein A or an anti-immunoglobulin.

Abstract: A buffered aqueous composition is useful simultaneously as a wash solution and a dye-providing composition in specific binding assays involving enzyme-labeled specific binding reagents. The wash composition includes a dye-providing composition, a buffer and an organic solvent having a certain molecular weight and water-solubility. Another useful composition includes a particulate substrate having avidin attached thereto, and a peroxidase reducing agent. Either composition can be provided in a diagnostic test kit, and can be used to detect a specific binding ligand in assays.

Abstract: The present invention provides monoclonal antibodies demonstrating specific reactivity with HIV-1 p24. One monoclonal antibody designated 31-42-19 recognizes an unique epitope on HIV-1 p24 that is not immunogenic in humans. 31-42-19 also reacts with an antigenically cross reactive epitope on HIV-2 p24. Another monoclonal antibody designated 31-90-25 recognizes an epitope within a highly immunogenic region of HIV-1 p24. The present invention also provides cell lines capable of producing these monoclonal antibodies. The invention also includes a highly sensitive enzyme immunoassay for the detection of HIV-1 p24 in biological fluids, using a monoclonal antibody mixture. The present invention further provides methods for the use of these monoclonal antibodies for the detection of anti-HIV-1 p24 antibodies and HIV-2 p24 antigen in biological samples.

Abstract: An in vivo method for preparing, inserting, isolating, collecting and assaying diagnostic ligates present in body fluids. Magnetically responsive particles with attached ligands specific for a particular ligate are introduced into the body fluid. Bonding between the ligand and ligate results in particle/ligand/ligate complexes. The complexes are removed by the application of a magnetic field and the complexes are permitted to cluster. The clusters are then quantitated to determine the concentration of the ligate in the body fluid. Associated materials and devices useful in the practice of this method are also provided.

Abstract: A novel material and device useful in solid-phase binding assays to determine the presence or amount of an analyte in a test sample, particularly antigens or antibodies, is disclosed. The material comprises a porous matrix of fibers and a plurality of substantially spherical, solid particles having an average diameter of from about 0.1 to about 5 microns. The particles are retained and immobilized upon the fibers of the matrix. Preferably, the particles have on their surfaces a substance capable of reaction with the analyte in the sample, and the average diameter of the particles is less than the average pore size of the matrix. The device, in a preferred embodiment, comprises a substantially planar layer of the described material.

Abstract: An apparatus is provided for the detection and semi-quantitative measurement of analytes. The assay results are visualized by the formation on a filter of a colored annular or circular spot, the diameter of the spot being related to the concentration of the analyte of interest. The filter on which the assay results are visualized is divided into multiple regions by strips of non-porous tape crossing the filter surface. The invention also includes a component for diluting sample to a suitable concentration for analysis, and dispensing the diluted sample onto the test filter.

Abstract: A rotary fluid manipulator utilizable as a diagnostic device includes a porous body having fluid passages defined therein by fluid blocking means in the porosities of the body such as openings or slots in the body or compaction of areas of the porous body to define fluid passages therebetween. Various substances or binding partners such as receptors, immunoassay or other assay test materials and test specimens can be deposited on the porous body to permit various types of tests to be made by rotation of the manipulator to cause conjunctive centrifugal and wicking induced flow of fluids deposited thereupon.

Abstract: An immunoassay method comprising applying an aqueous solution containing the analyte antigen to one end of a multi-zoned test strip device such that the solution moves along the strip by capillary action. The zones are arranged so that the solution (a) first contacts and reconstitutes dry, diffusible labelled component comprising colloidal gold conjugated to an antibody specific for said analyte antigen and then (b) contacts and reconstitutes dry, diffusible biotinylated second antibody specific for said analyte antigen such that a diffusible, dispersed sandwich reaction product forms. The reaction product diffuses along the strip with the solution and into a zone containing capture component consisting of a latex and avidin complex which avidin collects the reaction product by means of reaction with its biotin moiety. Thus, gold particles are collected and concentrated in the detection zone for visual determination.

Abstract: New and useful chromophores have been isolated from the reaction mixture of proteins exposed to reducing sugars in the presence of sulfite over time. The chromophores are believed to be intermediates in nonenzymatic polypeptide glycosylation. The measurement of this chromophore makes possible both qualitative and quantitative assessment of the presence of nonenzymatic browning. Diagnostic and test kits are also disclosed.

Abstract: Colloidal particles are converted into magnetic microagglomerates via manipulation of their colloidal properties, thereby facilitating their separation from solution.

Abstract: The invention relates to a heterogeneous immunoassay which is carried out using a multizoned test device. In particular, the invention involves the use of an inhibitor of a label which is used in the assay. The label which may be an enzyme, is attached to a receptor such as an antibody. The inhibitor is not acted upon by the label, but must be removed in order for a signal to be produced. Also described are test strips which can be used for the assay.