Abstract: A method for carrying out a binding assay is described wherein a member of a specific binding pair (sbp) and a sample are combined with a matrix of non-porous beads in a liquid medium under conditions such that the beads bind to the sbp member. The liquid medium is removed from the beads by aspiration using an aspiration tube having one or more orifices each of a diameter smaller than the minimum diameter of the smallest bead thereby allowing removal of the liquid medium while prohibiting aspiration of the beads.

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: A target substance is detected by a sandwich immunoassay using fine particle (A) having bound to it a fluorescer and an antibody reacting specifically with the target substance, and a fine particle (B) having bound to it a quencher and an antibody reacting specifically with the target substance, through a different antigenic determinant. Also disclosed is a competitive immunoassay having a fine particle (C) bound to it a fluorescer or a quencher, and an antibody reacting specifically with the target substance, a bound product (D) composed of the remainder of the fluorescer and the quencher, or a known amount of the target substance. Binding of the fluorescer and the quencher to the fine particle (A), (B) or (C) is affected so that the fluorescer and the quencher are covalently bound to a substance adsorbed on the fine particle.

Abstract: A method useful for determining the content of a first hemoglobin in a blood sample which also contains other forms of hemoglobin is based on capillary electrophoresis. In the method, a specific binding partner to the first form of hemoglobin is added to the sample, and the sample is then subjected to capillary electrophoresis. The method is particularly suited for the determination of the percentage of Hb A.sub.1c in a blood sample using anti-Hb A.sub.1c antibody.

Abstract: On a slab-like board formed of a transparent material is closely attached a wedge-shaped transparent cover member provided with a recess in a central inner portion, thereby to form a clearance. The height of the clearance between the recess and the board is configured to decrease continuously or in steps. When an immunological active substance such as a monoclonal antibody is caused to sensitize carrier particles F, and a reagent having the carrier particles F dispersed into a liquid medium mainly composed of the water is mixed with a specimen, the reaction will occur in which the flocculate is formed from plural carrier particles. When this reaction liquid is poured into the clearance through the opening, the reaction liquid penetrates in the direction having a narrower vertical spacing due to surface tension. A single carrier particle unflocculated can move deep within the recess because it is small in diameter, but the flocculate G is trapped on its way and can not move because of its size.

Abstract: Hybridomally produced monoclonal IgM antibodies having high affinity are useful for the immunoassay and purification of vital antigens.

Abstract: Disclosed is a primary chromatographic support containing an immobilized flocculating agent for use as a separation media for a secondary support consisting of microparticles used in affinity separation and heterogeneous immunoassays. In a specific embodiment, a flocculating agent such as polyethyleneimine is immobilized on a chromatographic resin packed in a column. The column so formed is then used to trap microparticles having an affinity ligand or binder for the ligand affixed thereon. Such microparticles are used as a solid support for the affinity reaction involved in a variety of immunoassay formats.

Abstract: The present invention relates to an apparatus for determining the presence or absence of a target analyte in a liquid sample, comprising:(i) a container capable of accommodating the liquid sample and having a transparent portion; and(ii) an insertion member which is capable of being inserted into the container comprising;a porous member which has a main surface and a reverse surface and which has on the main surface a substance capable of specifically binding to the target analyte; andan absorbent bonded to the reverse surface of the porous member;the porous member being supported in the insertion member whereby, when the insertion member is inserted into the container, the main surface can be observed from the outside of the container through the transparent portion of the vessel and the liquid sample is absorbed into the absorbent through the porous member.According to the analyzer of the present invention, the presence or absence of a target analyte in a sample can be easily determined.

Abstract: Peptides comprising between 20 and 39 amino acids capable of reacting with antibodies against the Sm-D polypeptide. These peptides may be used in a diagnostic method to detect of antibodies against the Sm-D polypeptide in a biological sample from a person suffering from systemic lupus erythematosus.

Abstract: A method is provided, in one embodiment, for the determination of an analyte in a biological fluid sample in the presence of a substance interfering with an assay for the analyte. This embodiment is implemented by using antibodies to cause the selective immunoreaction of at least one of the analyte or the interfering substance and then conducting an assay for the analyte in at least one of the immunoreactants or the non-reactants. Another embodiment provides a disposable reaction device to implement the method. The invention is applicable to the detection of a wide variety of analytes, including cholesterol in a targeted lipoprotein class in the presence of cholesterol in another class; to targeted isozymes of enzymes such as creatine kinase, lactate dehydrogenase, amylase, and alkaline or acid phosphatases in the presence of other isozymes; as well as to targeted immunoglobulins in the presence of non-targeted immunoglobulins.

Abstract: An assay is provided in which a target ligand is detected in a biological specimen. The method involves treating the target ligand with detergent and then binding the treated ligand to a particle by means of a capturing substance on the particle, thereby forming a complex. The complex is then applied to a porous membrane having a charge similar to that of a glass fiber filter in order to immobilize the complex in the porous membrane. The pore size of the membrane is substantially larger than the size of the complex such that the immobilization of the complex is substantially accomplished by means of the attraction of the complex to the charge of the porous membrane, and not as a function of the pore size of the membrane. Thereafter, the presence of the complex in the porous membrane is detected.

Abstract: A method for determining total analyte concentration in a sample having both free and bound analyte is described. This method involves (a) disassociating immune complexes, (b) assaying for the concentration of free analyte, (c) assaying at least once for the concentration of free analyte in the sample wherein said sample contains a known quantity of analyte which has been added to the sample, and (d) determining total analyte concentration from the assayed concentrations obtained in steps (b) and (c).

Abstract: The present invention provides unique prepared immunogens, site-specific polyclonal antisera and monoclonal antibodies against the DNA-binding domain of estrogen receptor protein, and immunoassay to determine the functional status of estrogen receptors in a cellular sample. Collectively or individually the component parts of the invention provide the ability not only to identify accurately the presence of human estrogen receptor but also the capability of determining whether the estrogen receptor exists in a functional or non-functional state.

Abstract: Method for monitoring patients having connective tissue autoimmune diseases comprising contacting patient specimens with (U1)RNA and detecting immune complexes formed, the level of reaction indicating the severity of the disease.

Abstract: A method, composition, device, apparatus, and kit for the determination of the presence or amount of an analyte by monitoring an analyte-mediated ligand binding event in a test mixture which contains the analyte to be assayed, a specific binding member, a Raman-active label, and a particulate having a surface capable of inducing a surface-enhanced Raman light scattering. The test mixture is illuminated with a radiation sufficient to cause the Raman-active label in the test mixture to emit a detectable Raman spectrum. The differences in the detected surface-enhanced Raman scattering spectra are dependent upon the amount of the analyte present in the test mixture. Thus, by monitoring these differences, the presence or amount of the analyte are determined.

Abstract: The present invention provides a method for type determination in body fluids of antibodies of a definite immunoglobulin class which are directed against an antigen A according to the immunoassay principle by incubation of the sample solution with at least two receptors R.sup.1 and R.sup.2, of which R.sup.1 is immobilizable and binds with the antibody to be determined and R.sup.2 is labelled and binds either with the antibody to be determined or with the antigen A, separation of the solid phase from the liquid phase and measurement of the label in one of the two phases, wherein the immunological reaction is carried out in homogeneous phase and the sample solution is incubated simultaneously with receptor R.sup.1 and an excess of human antibodies or fragments thereof which belong to the same immunoglobulin class as the antibody to be determined and are not bindable with the antigen A and subsequently receptor R.sup.2 and possibly further receptors are added thereto.

Abstract: A system for assaying a fluid sample, typically employing a fluorescent tag, the system comprising a lens capable of focussing both excitation and fluorescent radiation, a fluid-flow conducting conduit being provided in the lens extending transversely of the optical axis of and through the focal region of the latter. One or more mechanical screens are disposed adjacent the focal region in the conduit to arrest passage of beads as a function of bead diameter. The beads, precoated with at least a moiety of a ligand/conjugate complex, e.g. a specific-binding ligand, are preferably substantially transparent to both the excitation and fluorescent radiation.

Abstract: There are described a device and method for doing confined reactions such as PCR amplification and detection, wherein solids (e.g., beads) used to obtain separation between bound and "free" label reagents, are transferred from region to region, specifically through a wash liquid so as to wash off the "free" label reagent from the solids. Separate chambers have dividers that are overcome by piercing or by liquification, to create passageways for the transfer of the solids. The passageways remain contained within the device.

Abstract: A method is described for measuring the amount of analyte present in a sample containing the analyte using a homogeneous amperometric immunoassay. The analyte is chemically bonded to a suitable carrier molecule, which is also chemically bonded to an electroactive molecule. The electroactive molecule, such as ferrocene carboxylic acid, contains a redox center which is capable of transferring a charge to an electrode. A preferred carrier molecule is bovine serum albumin (BSA), while suitable analytes include digoxin, theophylline and HCG. The immunoassay is conveniently performed by applying a voltage to a set of electrodes.

Abstract: A method is described for the detection of anti-streptokinase antibodies in a sample which comprises detection of a complex between lactate dehydrogenase, streptokinase, and antistreptokinase antibodies. The method is useful for the detection of antistreptokinase antibodies in the serum of patients prior to clinical streptokinase administration.

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 labeled 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: 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 method of detecting target antibodies or antigens by reaction with specific binding partners thereto is disclosed. One of the target or the binding partner is bound to a carrier, and the other is unbound. The complex between the target and the binding partner, with one being carrier-bound, forms an optically detectable binding complex. A microreaction vessel having an upper portion, a transition portion and a lower portion is utilized, wherein the upper portion has a greater diameter or width than the lower portion, and the transition portion is situated between the upper portion and the lower portion, and is funnel shaped. The microreaction vessel contains a slurry or suspension of inert particles, and unbound target or binding partner thereto. A solution of the carrier bound target or binding partner thereto is added to the vessel, which is then centrifuged to produce an optical determination of the target.

Abstract: The instant invention is directed toward an immunoassay which can determine the presence of amphetamines in a sample suspected of containing amphetamine and/or methamphetamine by employing at least two conjugates, each comprised of a functionally similar label bound to an amphetamine analog and a methamphetamine analog respectively and an antibody to amphetamine and an antibody to methamphetamine wherein at least one of the antibodies is a monoclonal antibody.

Abstract: The invention relates to a method based on fluorescence, especially time-resolved fluorescence for quantitative assay of a bioaffinity reaction involving bioaffinity components. The method comprises the labelling of one or several of the bioaffinity components participating in the reaction with a lanthanide chelate, forming of a lanthanide chelate for a fluorescence measurement after the reaction, and measuring the fluorescence of the chelate. The lanthanide (Eu, Tb, Sm or Dy) is brought to a strongly fluorescent form before the fluorescence measurement by incorporating the lanthanide in an aggregated particle that comprises the lanthanide chelate and a chelate of a fluorescence-increasing ion (Y, Gd, Tb, Lu or La) to bring about a cofluorescence effect. An aliphatic or aromatic beta-diketone is used as the chelating compound in the aggregate.

Abstract: Biologically active reagents are prepared from particles of copolymers having highly active succinimid groups. The reagents are prepared by covalently attaching biologically active substances, for example antibodies, to the particles, directly or indirectly through amide groups by displacement of highly active succinimid groups on the particle surface. These reagents are used to advantage in analytical elements, methods for the detection of specific binding ligands (such as immunological species) and immunoassays, and in purification methods such as affinity chromatography.

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 primary chromatographic support containing an immobilized flocculating agent for use as a separation media for a secondary support consisting of microparticles used in affinity separation and heterogeneous immunoassays. In a specific embodiment, a flocculating agent such as polyethyleneimine is immobilized on a chromatographic resin packed in a column. The column so formed is then used to trap microparticles having an affinity ligand or binder for the ligand affixed thereon. Such microparticles are used as a solid support for the affinity reaction involved in a variety of immunoassay formats.

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: The invention concerns a method for the detection of an analyte in a sample liquid by an enzyme-immunoassay in which an enzyme-labelled compound is partitioned between a solid and a liquid phase and the amount of enzyme label in the liquid phase outside the solid phase is determined as a measure of the concentration of the analyte. The measurement is carried out in a non-porous molding having the liquid phase contained therein in contact with the solid phase. The method is particularly suitable for carrying out in a cuvette which can be filled via the porous matrix or on a test strip having a space in contact with the solid phase.

Abstract: A microorganism detection system provides initial warning, confirmation of dentity, and recognition of pathogenic factors in microorganisms from environmental samples. The method and apparatus of the invention uses different sized antibody coated microspheres which react with unknown antigens, are sized by electronic volume sizing, and are sorted by size. The sized particles are quantitated in addition to being sized. The microsphere sizes indicate the presence of specific microorganism groups.The samples can be further analyzed using fluorescent microspheres which agglutinate with the sized microspheres. The presence of specific microorganisms is indicated by a change in the fluorescence of the sample.

Abstract: The type of a blood specimen is determined by adding a portion thereof, either a diluted solution of its red cells or a portion of its plasma, to each of a multiplicity of wells in a transparent tray, by adding a blood type specific reagent to each of the wells in the tray, different reagents being added to different ones of the wells of the tray, periodically tilting the tray at a substantial angle of at least approximately 50.degree.

Abstract: Methods are disclosed for separating a component of interest from a mixture containing the component of interest and other components. The method comprises contacting a first liquid medium containing the component of interest and other components with a second liquid medium that is of different density than and/or of different viscosity than the first liquid medium. The contact is carried out in such a way that mixing of the media is minimized or avoided. The component of interest is bound to magnetic particles. The contacted first liquid medium and second liquid medium are subjected to a magnetic field gradient to allow the magnetic particles to migrate into the second liquid medium and separation of the component of interest from other components is realized. Also disclosed are assays employing the present method. Kits for carrying out the present method and assays are also disclosed.

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: The invention concerns a process for the preparation of hybridoma cells which secrete monoclonal antibodies specific for hirudin, the hybridoma cells themselves, the monoclonal antibodies specific for hirudin secreted by these hybridoma cells, derivatives thereof, and a process for the preparation of said antibodies and derivatives. These monoclonal anti-hirudin antibodies and their derivatives are useful for the determination of hirudin and as an antidote to hirudin. The invention also concerns test kits and pharmaceutical compositions comprising said monoclonal antibodies and/or derivatives.

Abstract: The invention provides for methods and compositions to detect the presence of anti-HLA antibodies, HLA antigen or preformed HLA-containing immune complexes in biological samples. The complement protein Clq is bound to a solid substrate, then mixed with a biological sample containing immune complexes. The immune complexes are preformed, or formed by adding HLA antigens to a biological sample containing antibodies to HLA, or alternatively, by combining a biological sample containing HLA antigens with defined antibodies to HLA. The immune complexes bind to Clq, and are then detected by the addition of a labeled reagent.

Abstract: Diluent and wash compositions are useful in a rapid and sensitive assay for detecting antibodies, and especially retroviral antibodies, in a biological specimen. The diluent composition is buffered to a pH of 6 to 10 and includes a protein or carbohydrate, a surfactant and a negatively-charged organic compound. The wash composition is buffered to a pH of 5 to 10 and includes a surfactant. These compositions can be included in a diagnostic kit. The method of this invention includes mixing the biological specimen with the diluent composition, forming an immunological complex between ligand and antibodies in the specimen and separating complexed materials from uncomplexed materials using a filtration membrane and a washing step. An enzyme labeled anti-antibody is added to form a ligand-antibody-antibody complex followed by its detection using suitable reagents.

Abstract: A cell surface antigen determination method for determining an immunocyte having an immune antigen-antibody complex composed of an antigen and an antibody combined therewith in a liquid which contains immunocytes having various antigens and also containing many kinds of antibodies, and an apparatus used in this method. In accordance with the inventive method and apparatus, non-specific reactions are restrained so as to reduce the background without using a complement.

Abstract: Specific binding methods are used for diagnostic assays and purification separations whereby the specific binding capture reagent is prepared from copolymers having highly reactive carboxy groups. These groups are extended from the polymer surface with a linking group having from 8 to 50 atoms in the chain and two or more alkylene, arylene, alkylenearylene or arylenealkylene groups. To these reactive groups is attached a biologically active substance such as a protein or oligonucleotide which then participates in the diagnostic assays or purification separation methods.

Abstract: The selectivity of immunoselection systems employing insolubilized avidin and biotinylated specific antibody is amplified, and nonspecific recovery is improved, by employing an indirect sandwich technique using a biotin-conjugated antispecies immunoglobulin that is directed to one or more nonbiotinylated specific antibodies in conjunction with insolubilized avidin. Specific cell populations can be removed and recovered from bone marrow, providing excellent recovery of bone marrow and preservation of hematopoietic stem cells for transplantation. Mixed populations of T cells or of tumor cells can be conveniently and simultaneously removed with minimal manipulation of the marrow cells. An improved positive immunoselection method provides viable and functional recovered cells, e.g., hematopoietic stem cells or activated killer cells, that can be clinically employed.

Abstract: Analytes, having a characteristic determinant that selectively interacts with a specific binding substance, are determined by coupling a reporter substance to the analyte, or to the specific binding substance, causing complex formation between the analyte and the specific binding substance in a test medium, separating the complexes thus formed from the test medium, and determining the presence or quantity of the analyte of interest by detecting the occurrence of the reporter substance in the complexes or the separated test medium. The determination is preferably performed on biomembrane-containing entities, such as cell subpopulations and/or subsets thereof, the reporter substance being stably associated with the lipid component of the biomembrane. Reagents and test kits are disclosed for performing the analyte determination.

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 method and device for testing for the presence of substances such as drugs in body fluids while simultaneously positively identifying the test subject. The device comprises an absorbent pad and a membrane mounted to the absorbent pad containing a plurality of separated areas provided with different immobilized ligand having a specific receptor site for capture or rejection of specific antigens produced by different predetermined drugs.

Abstract: A simultaneous dual analyte assay for determining the fertile period of the human menstrual cycle. The assay utilizes a capture reaction component consisting of P-3-G immobilized on a microporous membrane, a blocking reaction component consisting of anti E.sub.1 -3-G antibody, a labelled reaction component consisting of gold particle labelled anti E.sub.1 -3-G antibody, and an ambifunctional reaction component consisting of a hybrid immunoreactive substance having an anti P-3-G antibody binding site and a plurality of E.sub.1 -3-G determinant binding sites. An aqueous sample containing P-3-G and E.sub.1 -3-G is contacted with the components and the assay is calibrated to provide a positive assay result only when the concentration of P-3-G in the sample is less than a predetermined concentration and the concentration of E.sub.

Abstract: The present invention relates to an optical apparatus and a uniaxial method for rapidly measuring spectroscopically labelled specific binding analytes in a reaction assay mixture that contains unbound label without requiring the physical separation of the unbound label from the reaction mixture or sequential reagant additions and incubations. Moreover, the technique is equally applicable to measurements in either serum or whole blood.

Abstract: Disclosed is a method and a family of materials useful for removing immune complexes from blood preferentially to soluble antibodies. The material comprises analogs of proteins which bind to the Fc region of immunoglobulin. The analogs are produced by truncating or otherwise altering the amino acid sequence of the binding protein to reduce their affinity for Fc. An array of such analogs disposed about the surface of an insoluble matrix has the ability to form multiple points of attachment to the multiple Fc's in a complex so as to bind complex strongly, whereas only weak associations are developed between the Fc region of soluble IgG and individual analogs. The preferred analogs are truncated proteins homologous to a portion of the domains of Protein A or Protein G which bind with Fc. Complex may be removed from whole blood or serum using the material and conventional plasmapheresis techniques.

Abstract: A method of high sensitivity immunoassay characterized by inclusion of processes (A), (B), (C) and (D) described below.Process (A): A process of binding of a solid carrier and a complex comprising the specific antibody or antigenic substance to be assayed in the test solution and one or more active components.Process (B): A process of dissociating said complex from the solid carrier.Process (C): A process of binding this complex to another solid carrier.Process (D): A process of assay for the complex on the solid carrier mentioned in the description of process (C) above.Permitting rapid, high sensitive immunoassay irrespective of whether the subject of assay is an antibody or an antigen, the method of the present invention is very useful for quick diagnosis of various diseases.

Abstract: The invention relates to an assay for determining an analyte in a fluid sample. Three receptors are used, with formation of a quaternary or four member complex. One of the receptors is bound to a solid phase, and binds to complexes of another receptor and the analyte. A third receptor is labelled, and it, too, binds analyte. The invention also involves the use of a displacement solution to wash fluid sample from solid phase after the first portion of the quaternary complex forms, i.e., prior to binding with the labelled receptor.

Abstract: A method of, apparatus for and test kit for determining the presence of an analyte in a sample during an immunoassay, wherein the sample is contacted with a porous carrier carrying, an immobilized form on its surface, a binding partner for the analyte of interest, the carrier is backwashed to remove unbound material at said surface, and the presence of analyte bound to the carrier surface is determined.

Abstract: Methods for determining the presence of a first ligand, preferably a hapten, in a sample suspected to contain the first ligand are provided, along with reagent systems and apparatus suitable for performing the methods. The methods depend upon a color visualization indicating the presence or absence of the first ligand in the sample. Preferred methods comprise contacting the sample with a reagent system which comprises: (1) colored particles which bear on their surface a second ligand which may be the same as or different than the first ligand; and (2) an amount of a receptor which is specific for the first ligand and the second ligand, wherein the amount is sufficient to stabilize the particles. The methods further comprise passing the contacted sample and reagent system through a filter, and then analyzing the color of the filtrate. The presence of ligand in the sample is established where the color of the filtrate is substantially different from the color of the ligand-bearing particles.