Abstract: In order to measure the concentration of an analyte in a liquid sample the sample is contacted with a receptor molecule having binding sites for the analyte and labelled with a first marker, whereby a fraction of the binding sites on the receptor molecule become occupied by the analyte, the sample being contacted with such a small amount of the receptor, having regard to its affinity constant with the analyte, that only an insignificant fraction of the analyte becomes bound to the receptor. The receptor having fractionally occupied binding sites is then back-titrated by means of a back-titration technique involving a system including a second marker different from the first, and the relative strengths of the two signals produced by the two markers are measured to provide a value representative of the fractional occupancy of the binding sites on the receptor molecule by the analyte.

Abstract: The present invention provides methods for determining the concentration of analytes in liquid samples in which the amount of binding agent having binding sites specific for a given analyte in the liquid sample is immobilized in a test zone on a solid support, the binding agent being divided into an array of spatially separated locations in the test zone. The concentration of the analyte is obtained by back-titrating the occupied binding agent with a developing agent having a marker and integrating the signal from each location in the array. The present invention also provides a method for determining a value representative of a fraction of binding sites of the binding agent which are occupied by the analyte, comprising immobilizing the specific binding agent on a solid support, wherein the specific binding agent used for the fractional occupancy is present in an amount less than 0.

Abstract: A method for determining the concentration of an analyte 6 in a liquid sample is described. The method uses a binding agent 2 capable of binding the analyte 6 and first and second developing agents 8, 12, the first developing agent 8 capable of binding to unoccupied binding sites on the binding agent 2 and having a first marker 10, the second developing agent 12 capable of binding to the bound analyte or to the occupied binding sites and having a second marker 14 different from the first. The concentration of the analyte is determined by measuring the signals from the markers on first and second developing agents 8, 12. Thus, the method combines the competitive and non-competitive methods of the prior art and preferably has the advantage of extending the working range and/or sensitivity of the assay. A kit for performing the assay is also disclosed.

Abstract: A method for determining the ambient concentrations of a plurality of analytes in a liquid sample of volume V liters, comprisesloading a plurality of different binding agents, each being capable of reversibly binding an analyte which is or may be present in the liquid sample and is specific for that analyte as compared to the other components of the liquid sample, onto a support means at a plurality of spaced apart locations such that each location has not more than 0.1 V/K, preferably less than 0.

Abstract: A method of measuring the ambient concentration in a fluid, especially a body fluid, of an analyte, such as a hormone or other biologically active material, whose concentration in the fluid is dependent on thedilution of the fluid is disclosed. The fluid is contacted with a trace amount of a binding agent, such as an antibody, specific for the analyte, the proportional occupancy of binding sites on the binding agent is determined and from that figure the analyte concentration is estimated without the need to measure accurately beforehand the volume of the fluid or fluid sample being tested. It is therefore possible to design a concentration-measuring device for insertion into a body fluid of a living creature for in situ measurement of concentration.

Abstract: A binding assay process for an analyte, using a capture binding agent with binding sites specific for the analyte and a developing binding material capable of binding with the bound analyte or with the binding sites on the capture binding agent either occupied by the bound analyte or the remaining unoccupied binding sites, employs the capture binding agent in an amount such that only an insignificant fraction of the sample analyte becomes bound to the capture binding agent, which is preferably provided at high surface density on microspots. A label is used in relation to the developing binding material and is provided by microspheres which are less than 5 .mu.m and carry a marker preferably fluorescent dye molecules. To determine the concentration of sample analyte, the signal strength, which represents the fractional occupancy of the binding sites on the capture binding agent by the analyte, is compared with a dose-response curve computed from standard samples.

Abstract: A method for determining the ambient concentrations of a plurality of analytes in a liquid sample of volume V liters, comprisesloading a plurality of different binding agents, each being capable of binding specifically and reversibly an analyte of interest onto a support means at a plurality of spaced apart locations such that not more than 0.

Abstract: A method for determining the amount of free ligand in a test ample where the ligand is also present bound to one or more endogenous receptors, comprising combining the test sample, ligand receptor and unlabelled, differential binding ligand analogue, incubating to permit the free ligand and unlabelled, differential binding ligand analogue to compete for the ligand receptor separating the ligand analogue, determining the amount of ligand receptor bound to the ligand or to the ligand analogue, and correlating the amount of bound ligand receptor to the amount of free ligand present in the test sample.

Abstract: In order to measure the concentration of an analyte in a liquid sample the sample is contacted with a receptor molecule having binding sites for the analyte and labelled with a first marker, whereby a fraction of the binding sites on the receptor molecule become occupied by the analyte, the sample being contacted with such a small amount of the receptor, having regard to its affinity constant with the analyte, that only an insignificant fraction of the analyte becomes bound to the receptor. The receptor having fractionally occupied binding sites is then back-titrated by means of a back-titration technique involving a system including a second marker different from the first, and the relative strengths of the two signals produced by the two markers are measured to provide a value representative of the fractional occupancy of the binding sites on the receptor molecule by the analyte.

Abstract: A method of measuring the concentration of a free ligand in a biological fluid containing the free ligand and ligand bound to endogenous binding agent, by the steps of(a) mixing a sample of the fluid with an analogue of the ligand, a specific binder with which the free ligand and the ligand analogue bind, and an exogenous binding agent which binds the ligand analogue but not the ligand, either the ligand analogue or the specific binder being labelled,(b) incubating the resulting mixture,(c) determining either the amount of the labelled analogue bound or the amount of labelled specific binder bound, or not bound, to the ligand analogue, and(d) correlating the determined amount to the amount of free ligand present in the sample.The method is useful to measure concentration of free thyroid hormones and other hormones in body fluids, employing antibodies specific to the ligand analogue as the exogenous binding agents.

Abstract: A method for indirect measurement of the concentration of a free ligand in a liquid sample also containing the ligand bound to endogenous binding material, comprising the steps of performing two separate measurements, wherein the first measurement is used to determine the total concentration of free and reversibly bound ligand in the sample to be tested, and the second measurement comprises the steps of (i) exposing separately to a known amount of a labelled ligand (a) the sample to be tested, and (b) each of a plurality of standard solutions containing known concentrations of the free ligand, (ii) thereafter exposing each resulting mixture from (i) (a) and (i) (b) separately to an immobilized binding agent to bind a portion of the free labelled ligand and a similar proportion of the free unlabelled ligand to the immobilized binding agent in each mixture, (iii) separating the immobilized binding agent with its bound ligand from the residual material in each mixture, (iv) measuring the proportion of labelled l

Abstract: In an instrument for measuring radioactivity, the total measuring time for each sample is optimized by considering the maximum acceptable total counting error as well as the count rate. Each sample is counted for a period of time that is considerably shorter than the required measuring time but long enough to estimate the average pulse frequency, then the measuring time is determined as a function of the estimated pulse frequency and of the experimental error as determined by the channels ratio method.