Abstract: A method for counting living cells of microbes in a fluid sample continuously while flowing the sample using an apparatus which comprises a system for supplying at a predetermined rate to the flow line of the sample a reagent, such as, a derivative of fluorescein, capable of reacting with one or more substances intrinsic of the living cell, such as enzyme, to form an accumulative fluorescent product within the living cells; a reactor inserted in the flow line of the sample and being provided for the reaction of the reagent with the cell-intrinsic substance in the living cells; a photometric detection system arranged subsequent to the reactor for detecting fluorescence emitted as individual luminous point from the fluorescent product in each of the living cells floating in the flowing sample upon irradiation of the fluorescent product by an exciting ray; and an electronic unit including a pulse counter for counting electric pulses produced from each fluorescence from the luminous point.

Abstract: A method for correcting for light scattering affects obtained from a sample to which a fluorophore has been added. In accordance with the invention, a sample to which a fluorophore has been added is irradiated with light in the adsorption band of the fluorophore such that the fluorophore emits light at a different intensity. By manipulating the pH of the sample, and obtaining both pre- and post-manipulation emission light intensity readings, the value of the reading attributed to "light scattering" can be determined, such that correction of an erroneous fluorescence reading can be obtained.

Abstract: Disclosed is an assay system including a compound comprising an analyte-specific moiety having substituted thereon a polymer comprising plurality of self-quenching emitter moieties and a plurality of isocharged functionality separating the emitter moieties. The present invention provides compounds that overcome the undesirable effects of self-quenching when multiple emitter moieties are used for labelling of assay reagents. Avoidance of this self-quenching phenomenon by the compounds of the invention makes it possible to introduce a more concentrated degree of labelling on to analyte-specific molecules such as oligo nucleotide probes, antibodies and other specific binding proteins and analyte-specific polysaccharides. Therefor, it is possible to effect greater assay sensitivity because the number of labels per recognition molecule(analyte-specific moiety) can be increased beyond the point previously possible without the reduction in signal caused by self-quenching.

Abstract: In an assay in which a ligand is labelled by conjugation to a dihydrophthalazinedione (DPD), e.g. luminol or isoluminol, and the conjugated DPD is reacted with an oxidant, e.g. hydrogen peroxide, and an active heme group catalyst, e.g. microperoxidase, the light intensity is enhanced by certain sterically hindered amines defined as saturated bicyclic compounds having a nitrogen atom at one or both bridgehead positions or a piperidine ring compound having four C.sub.1-4 alkyl groups at the 2- and 6- positions. 1,4-Diazabicyclo[2.2.2]-octane, known as "DABCO" is preferred.

Abstract: A system for rapid microbead calibration of a flow cytometer including a suspension of quantitative fluorescent microbead standards and analytical software. The software is used to take information on the microbead suspension from a flow cytometer and analyze data, smooth curves, calculate new parameters and notify of expiration of the system.

Abstract: A method of measuring at least one of a catecholamine and its metabolite including a biological sample pretreatment process, a fluorescence inducing process of converting into a fluorescence inductor the at least one of a catecholamine and its metabolite in the biological sample subjected to pretreatment by means of a fluorescence inducing reagent, and a measuring process of separating and measuring said fluorescence inductor by liquid chromatography, said method being characterized by addition of a specified volume of maleimide before said process of making the biological sample fluorescent.

Abstract: A method, a sensor and apparatus for detecting biological activities in a specimen, for example in a blood sample, are provided in which a sealable container is sealed with a culture medium therein into which the sample is introduced, metabolic processes are enhanced in the presence of microorganisms in the sample and changes taking place in the concentrations of the substances. Such processes are detected and monitored with an excitation and detection assembly assigned to concentration sensors, in the form of optodes which are optically coupled to the excitation and detection assembly and to thereby to an evaluation unit for determining concentration changes of the substances over time as indications of the presence of microorganisms.

Abstract: A process for assaying at least one analyte uses a tracer which includes multiple detectable substances. A tracer composition includes at least one ligand labeled with a particulate label, the particulate label containing at least one detectable substance. Two or more detectable substances in the assay may be in the same particulate label or in different particulate labels conjugated to different ligands.

Abstract: A method for rapidly lysing liposomes having transition temperatures in the range of 35.degree. to 65.degree. C. is provided. Such liposomes are treated with a surfactant including ##STR1## wherein x represents an average of 9 or 12. The method is applicable to fluorescence immunoassay procedures.

Abstract: Methods for characterizing and distinguishing reticulocytes and mature red blood cells use reagent compositions which include an organic cationic dye for staining the reticulocytes in the blood sample and a buffer solution for maintaining a pH of about 6 to about 9. The dyes may be the red excitable fluorescent dye Oxazine 750, or the blue excitable fluorescent dyes Acridine Orange or derivatives of Acridine Orange.

Abstract: A process for preparing phycoerythrin from Bangia atropurpurea or Porphyra angusta is disclosed. Spores of Bangia atropurpurea or Porphyra angusta, derived from their thalli, are cultivated under a controlled condition to germinate filaments. Phycoerythrin is then resulted from the extraction of filaments which are processed through drying powder-mill grinding, water or phosphate percolating and ammonium sulfate salting-out. The phycoerythrin is further purified by gel filtration. This process yields the phycoerythrin of 99% purity.

Abstract: Methods for characterizing and distinguishing reticulocytes and mature red blood cells use reagent compositions which include organic cationic dyes for staining the reticulocytes in the blood sample and buffer solutions for maintaining a pH of about 6 to about 9. The dyes may be the blue absorption dyes Oxazine 750 or New Methylene Blue.

Abstract: The invention relates to rare earth cryptates consisting of at least one rare earth salt complexed by a macropolycyclic compound corresponding to one of formulae I or II below, in which:the ring ##STR1## is the N.sub.2 O.sub.4 macrocycle, the N.sub.2 O.sub.3 macrocycle or the bis-bipyridine macrocycle;Y is a spacer arm or group which consists of a divalent organic radical selected from linear or branched C.sub.1 to C.sub.20 alkylene groups optionally containing one or more double bonds and/or optionally being interrupted by one or more heteroatoms such as oxygen, nitrogen, sulfur or phosphorus, or from C.sub.5 to C.sub.8 cycloalkylene groups or C.sub.6 to C.sub.14 arylene groups, the said alkylene or arylene groups optionally being substituted by alkyl, aryl or sulfonate groups;Z is a functional group capable of bonding covalently with a biological substance;R is a methyl group or represents the group --Y--Z; andR' is hydrogen or a group --COOR", in which R" is a C.sub.1 to C.sub.

Abstract: The complexing of an antibody-antigen binding pair is determined by observing the change in fluorescence of a pH-sensitive fluorochrome attached to one of the members of the binding pair. When the binding is conducted in a solution having a pH other than the isoelectric point of the antibody, there will be a change in the pH of the microenviromnent surrounding the fluorochrome. This change will correspond to a change in the observed fluorescent intensity. Either member of the binding pair can be labeled, and combined with that member whose presence is suspect, in an immunoassay.

Abstract: A method and apparatus for producing detectable intestinal parasites. The method includes obtaining an intestinal mucosa sample (e.g. feces) having intestinal parasites, such as Dienamoeba fragilis; and contacting the obtained intestinal mucosa sample with an acridine base compound (e.g. acridine orange and/or acridine yellow, etc.) such that the intestinal parasites become differentially stained and detectable by a human eye when viewed through a fluorescence microscope. The apparatus includes a kit or the like which includes at least one vessel or vial. Preferably, two vials are contained within the kit with one vial having an isotonic salt solution including a salt, such as sodium chloride, potassium phosphate, etc., and the other vial containing an acridine biological staining compound.

Abstract: Enzymatically cleavable chemiluminescent 1,2-dioxetane compounds capable of producing light energy when decomposed, substantially stable at room temperature before a bond by which an enzymatically cleavable labile substituent thereof is intentionally cleaved, are disclosed. These compounds can be represented by the formula: ##STR1## wherein: X and X.sup.1 each represent, individually, hydrogen, a hydroxyl group, a halo substituent, an unsubstituted lower alkyl group, a hydroxy (lower) alkyl group, a halo (lower) alkyl group, a phenyl group, a halophenyl group, an alkoxyphenyl group, a hydroxyalkoxy group, a cyano group or an amide group, with at least one of X and X.sup.1 being other than hydrogen; andR.sub.1 and R.sub.2, individually or together, represent an organic substituent that does not interfere with the production of light when the dioxetane compound is enzymatically cleaved and that satisfies the valence of the dioxetane compound's 4-carbon atom, with the provisos that if R.sub.1 and R.sub.

Abstract: Disclosed are immunofluorescence staining methods which increase the likelihood that antibodies expressed by a single B cell selected and sorted by fluorescence activated cell sorting are specific for the antigen of interest, and which also allow selection of B cells expressing antibodies of high affinity for the antigen of interest. The selection for B cells expressing antibodies to specific antigens is increased by labeling B cells with at least two antigen probes, where each antigen probe includes the antigen of interest and is labeled with a different fluorochrome. The positive selection is preferably combined with a negative selection step, in which autofluorescent cells and sticky cells are excluded out. The specificity of sorting of the desired B cells can be further enhanced by staining those antigen-specific B cells which produce the immunoglobulin isotype (typically IgG), with targeting molecules reactive with a B cell marker, such as .gamma.

Abstract: The invention relates to microparticles incorporating a series of two or more fluorescent dyes having overlapping excitation and emission spectra allowing efficient energy transfer from the excitation wavelength of the first dye in the series, transfer through the dyes in the series and re-emitted as an optical signal at the emission wavelength of last dye in the series, resulting in a desired effective Stokes shift which is controlled through selection of appropriate dyes.

Abstract: An analyzer has a reaction disk for holding a plurality of reaction containers and a fluorophotometer for measuring fluorescence stemming from solutions in the containers. Most of the containers contain solid phases attached with antibodies but at least one container does not contain any solid phase. In normal operation of the analyzer, a test sample containing antigens and a latently fluorescent reagent such as an antibody labeled by an enzyme are added to a container containing a solid phase. In this container, a fluorescent substance is created through an enzyme reaction. Light is irradiated on the container and the fluorescence emitted from the fluorescent substance is measured. While measuring test samples, fluorescence stemming from a reference sample, such as quinine sulfate, is measured to produce values for the reference sample by which measured values for the test samples are corrected.

Abstract: The invention relates to unsymmetrical cyanine dyes with a cationic side chain, typically benzothiazole or benzoxazole derivatives, that exhibit enhanced fluorescence on binding with DNA or RNA, where such fluorescence can be used for evaluating the presence of nucleic acid polymers. The dyes generally have the formula: ##STR1## where R.sup.1 is an alkyl group having 1-6 carbons; X is 0, S, or NR.sup.2, where R.sup.2 is an alkyl group having 1-6 carbons, or CR.sup.3 R.sup.4, where R.sup.3 and R.sup.4, which may be the same or different, are alkyl groups having 1-6 carbons;n=0, 1, or 2;Z.sup.1 and Z.sup.2, which may be the same or different, are independently hydrogen, an alkyl group having 1-6 carbons, or aryl, or Z.sup.1 and Z.sup.2 taken in combination complete a 6-membered aromatic ring;Y is HC.dbd.

Abstract: A substance having binding sites for at least two molecules may be detected within a sample. A molecule which can be recognized by the substance is labelled such that when at least two of the labelled molecules are bound the binding sites on the substance, the labels on the molecules electronically interact with each other and vary the wavelength dependance of their spectra. This variation in the spectra of the label can be detected. If the sample is suspected of containing the unlabelled form of a molecule, such as biotin or cocaine, a known amount of the above substance, along with a known amount of the corresponding labelled biotin or cocaine is added to the sample. In this instance, the amount of the suspect molecule in the sample is then determined by the extent to which the variation in the spectra of the label has been reduced. Alternatively, the present invention can be used to determine the binding characteristics of the substance within the sample.

Abstract: A method of setting up a flow cytometer using microbeads fluorescing at a plurality of wavelengths, control cells for each of said wavelengths, certified blank microbeads. The blank microbeads are run and the PMT voltages are adjusted so that the blank microbeads are on scale on the flow cytometer. The control cells are run and the photomultiplier tube voltages are adjusted so that the single population falls in selected channels. The fluorescent microbeads are run on the flow cytometer and the Target Channels for the flow cytometer are determined.

Abstract: This invention relates to a method for simultaneously detecting live and dead cells using two fluorogenic reagents: calcein AM and ethidium homodimer. Live cells are distinguished by an intense uniform green fluorescence generated by the enzymatic hydrolysis of calcein AM: ##STR1## Dead or damaged cells are distinguished by a bright red fluorescence resulting from nucleic acids stained with ethidium homodimer: ##STR2## The assay is useful to determine cell viability and to monitor cytotoxicity agents or events.

Abstract: A hematological specimen for classifying and counting leukocytes with a flow cytometer is prepared. A sample to be assayed is prepared by eliminating influences of erythrocytes from a hematological sample without changing leukocytes morphologically; adjusting the pH value to a level suitable for staining; and staining the leukocytes with at least two dyes including Astrazon Yellow 3G capable of specifically staining at least basophils and immature granulocytes and Neutral Red capable of specifically staining at least eosinophils. Thus leukocytes contained in the hematological sample can be classified at least three or six groups including immature granulocytes by measuring a single specimen with a flow cytometer.

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: Compounds which are useful as substrates for enzymes are disclosed. An enzyme-controlled process is provided for generating a colored species from an initially substantially colorless material as a result of enzymatic attack. The process can be exploited to provide an enzyme-amplified diagnostic assay method to detect an analyte of interest present in a test sample.

Abstract: A process of tumor identification comprising administering a carotenoporphyrin to a tumor-bearing mammalian host and irradiating the mammalian host with light whereupon the carotenoporphyrin, which has been preferentially taken up by the tumor tissue, fluoresces and permits precise identification of the location, size and shape of the tumor tissue. An improved process of synthesizing carotenoporphyrins 1-5 is also provided.

Abstract: Energy-transfer systems which can be used, inter alia, for measuring distances within or between different molecules are described, comprising derivatives of lumazine and ruthenium, in particular derivatives of DNA or RNA sequences.

Abstract: Novel pyrene-trisulfonate derivatives and the use thereof in a method for the determination of glycohydrolytic enzyme activity are provided. The method comprises the steps of (a) forming a test solution comprising a test sample containing the glycohydrolytic enzyme and a pyrene-trisulfonate derivative of the present invention, wherein the derivative is hydrolyzed by the glycohydrolytic enzyme to result in the formation of free 8-hydroxy-1,3,6-pyrene trisulfonate as a function of, and which can be correlated to, the amount of the glycohydrolytic enzyme present in the test sample, and (b) measuring and correlating either the intensity of fluorescence, or the optical density, of the test solution to the presence or amount of the glycohydrolytic enzyme in the test sample. A preferred pyrene-trisulfonate derivative is pyrene-1,3,6-trisulfonic acid) 8-.beta. -D-glucuronide for the determination of .beta.-D-glucuronidase for the diagnosis of periodontal disease.

Abstract: This disclosure related to a method and reagents for determining tetrahydrocannabinoids (THC) and THC metabolites in a biological fluid such as urine. In particular, this disclosure relates to a fluorescence polarization immunoassay procedure for determining the presence of THC and to a novel class of tracer compounds employed as reagents in such procedures. The procedure described also provides for novel wash reagent for a THC fluorescence polarization assay.

Abstract: A new and improved test device and method of determining the presence or concentration of a predetermined analyte, such as glucose, cholesterol or occult blood, in a test sample are disclosed. The test device includes a test pad comprising a suitable carrier matrix incorporating an indicator reagent composition capable of interacting with the predetermined analyte to produce a detectable or measurable response.

Abstract: A hematological specimen for classifying and counting leukocytes with a flow cytometer is prepared. A sample to be assayed is prepared by eliminating influences of erythrocytes from a hematological sample without changing leukocytes morphologically by adding a first aqueous solution of a low osmotic pressure including a buffer for adjusting the pH value within an acidic region and a second aqueous solution including an osmolarity compensating agent and a buffer for giving pH value suitable for staining, optionally further adding a salt, which dissociates into ions in aqueous solutions so as to control the electrical conductivity of the aqueous solution at a preferable level, while damaging the cell membranes of erythroblasts contained in said sample; and staining the leukocytes with at least four dyes including Astrazon Yellow 3G and Neutral Red.

Abstract: A method and compounds useful for this method are described for enzyme-amplified signal detection in analytical assays requiring extremely high detection sensitivity which uses a substrate capable of being transformed by an enzyme from a compound which does not form a luminescent lanthanide chelate into a product which forms a luminescent lanthanide chelate. The method in which a substrate not capable of forming a highly luminescent lanthanide chelate is enzymatically altered to produce a product which forms a highly luminescent lanthanide chelate and hence is particularly useful in time-resolved luminescence analysis as required in many different heterogeneous or homogeneous assay formats is described herein.

Abstract: The method for demonstrating the presence of an activity of an enzyme by(a) incubating said enzyme with a fluorogenic substrate A which is converted by the enzyme to a product B differing from A in respect to its fluorescent properties, A and/or B carrying a chromophore which is a triplet sensitizer having a triplet energy level above the excitation energy level of a lanthanide ion selected from the group consisting of Eu.sup.3+, Tb.sup.3+, Dy.sup.3+ and Sm.sup.3+ and which is capable of chelating said lanthanide ion by means of an oxygen or nitrogen atom in said chromophore, and that B differs from A either by(i) carrying a different chromophore, or(ii) having a different chelating ability, and(b) measuring the change in fluorescence caused by said enzyme.

Abstract: A biologic sample such as feces, sputum, cervical tissue, pleural fluids, exudates, cytologic specimens, or the like, is tested for the presence or absence of: ova; parasites; microorganisms; inflammatory, neoplastic tissue cells; or other target materials which are indicative of infestation, disease or infection. The sample is mixed with a buffer fluid and placed in a transparent tube which contains a volume-constricting cylindrical insert for gravimetric separation of components of the sample. The mixture is centrifuged, and the annular space between the insert and tube bore is examined under magnification for the presence of the target materials.

Abstract: A class of fluorescent rare earth chelates and the ligands upon which they are based whose molecular structure incorporates a plurality of substituted arylpyridine diacid units attached to a central template structure is disclosed. These ligands function as efficient energy transfer groups in fluorescent tagging reagents and tracers.

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: An improved fiber optic sensor, sensing apparatus, and methods for making optical detections are provided. The fiber optic sensor employs a fiber optic strand to convey light energy, an immobilized polymeric reaction matrix, and at least one controlled release polymeric carrier within said reaction matrix comprising a controlled release polymer material and a releasable reagent formulation able to react with the analyte of interest. The optic sensors and sensor construction have been demonstrated to be both functionally useful and long serving in duration.

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: 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: Enzymatic immunoassay for estimating the concentration of antigen or antibody comprising bringing an antigen-antibody complex, which is labelled by an enzyme and is present heterogeneously in a solution, into contact with a substrate where pH of the solution is so adjusted as to be suitable for the enzyme to be activated and also for measuring the fluorescence of the substrate, measuring the time-variation of fluorescent intensity of the substrate produced by the enzyme reaction, and estimating the concentration of the antigen or the antibody from the slope of the substantially linear portion, on a characteristic curve representing variation of the fluorescence intensity with the time.Fluorescence is measured while magnetic beads with antigen-antibody complex attached are oscillated at a specific frequency.

Abstract: A carrier having at least one kinetics and fluorescence enhancing support and a dry substance selected from the group consisting of fluorogenic substrates, B methylumbelliferone, 7-amino-4-methyl coumarin, B-napthylamine, fluoroscein, and resorufin deposited on the support demonstrates substantial enhancement of hydrolysis kinetics and fluorescence over pure liquid systems. When the device has a plurality of supports and the supports have different fluorogenic substrates an enzyme rate-of-reaction profile representative of a microorganism in the suspension can be determined and used to identify the organism. The device can also be used to characterize enzymes expressed by other biological specimens.

Abstract: A mass biosensor method provides enhanced quantification of analyte concentrations in a sample. In a direct approach, an analyte is derivatized to form an analyte chelate and then specifically bound to a sensor. In an indirect approach, a complement of the analyte is derivatized to form a complement chelate which is then bound to a sensor. In a direct/indirect hybrid approach, an analog of the analyte is derivatized to form an analog chelate that is bound to a sensor in competition with the sample analyte. In all three approaches, mass measurements taken as the ligand chelate attaches to the sensor permit the concentration of the analyte in the sample to be calculated. Once measurement is completed, a dissociation treatment is applied to dissociate the derivatized species from the sensor so that the sensor can be reused. The effects of the dissociation treatment can be monitored using phosphorescence detection.

Abstract: Genotoxic chemicals are an existing wide-spread health hazard to the human population. Advances in genetic toxicology testing have made it possible to assay potential mutagens, carcinogens, teratogens and clastogens in the environment. The mouse micronucleus assay provides an example of an excellent test for genetic damage to cells. When chromosome breaks occur in the blood stem cell population, the damaged piece of chromosome remains behind as a micronucleus in the normally DNA deficient red blood cells. However, currently available manual micronucleus assays are costly, time consuming, and labor intensive. In addition, the statistics are often marginal since the number of micronucleii (MNs) in 1000 polychromatic cells are scored manually, yielding limited amounts of data. This invention discloses the means for assaying the change in micronucleated cells by high speed flow cytometry.

Abstract: The invention concerns peptides which react immunochemically with antibodies directed against NANBH. A method for the detection of NANBH or anti-NANBH in a test fluid, an immunochemical reagent and a testkit to be used when applying said detection methods belong to the invention.

Abstract: A quantitative, sensitive, One-Step In Situ hybridization assay is provided which will detect as few as 1-5 copies of target biopolymer per cell and may be accomplished in 5 minutes to 4 hours. There is provided a simultaneous assay for detecting multiple biopolymers within the same cell.

Abstract: A reagent for proteolytic enzyme assays has the general formula ##STR1## where RCO-- is an enzyme reactive acyl, such as an amino acid, peptide or substituted amino acid or peptide. The reagent may by hydrolyzed by proteolytic enzymes and developed to form a distinctive color. The reagent may be formed by reacting RCOOH with N-hydroxysuccinimide to form the acyl N-hydroxysuccinimide ester. The ester may then be reacted to form the reagent.

Abstract: The invention provides a method capable of determining the presence or absence of each of a plurality of different ligands in a specimen. The specimen is contacted with a predetermined number of different homogenous populations of fluorescent beads having one or more predetermined antiligands affixed to their surface. The specimen and bead mixture is analyzed using a means having a single parameter of measuring fluorescence per ligand to determine the number of non-agglutinated beads, the number of agglutinated beads, the number of bead aggregates, and for each aggregate, the number of beads its comprises. This information is used to correlate the presence or absence in the specimen of each of the different ligands analyzed for. The method of the invention thus provides for the simultaneous determination of a predetermined number of ligands in a specimen using only a single bead contacting step.

Abstract: A reagent for proteolytic enzyme assays has the general formula ##STR1## where RCO-- is an enzyme reactive acyl, such as an amino acid, peptide or substituted amino acid or peptide. The reagent may be hydrolysed by proteolytic enzymes and developed to form a distinctive color. The reagent may be formed by reacting RCOOH with N-hydroxysuccinimide to form the acyl N-hydroxysuccinimide ester. The ester may then be reacted to form the reagent.

Abstract: The performance of double receptor, specific binding assays is improved by use of a receptor complex having the structureA.sub.BL (BL).sub.n A.sub.1wherein BL is a binding ligand, A.sub.BL is a receptor specific for binding ligand, A.sub.1 is a receptor, BL is covalently bonded to A.sub.1 and A.sub.BL is reversibly bonded to BL. Generally A.sub.BL is absorbed onto an insoluble surface and A.sub.1 is an antibody to the substance being assayed. The complex has particular utility in coated tube and rechargeable radioimmunoassay systems.