Immunoassay using test strip with immobilised antibody - based on displacement of tracer from antibody by analyte, esp. for determn. of pollutants

摘要

Immunoassay for determn. of an analyte (5) in a sample, using a test strip (1) of absorbent material with a zone in which an analyte-specific antibody (3) is immobilised, comprises (a) binding a 'tracer' (4) to the antibody, where the tracer is an analyte conjugate (6) capable of binding a labelled reagent, and where the antibody has greater affinity for the analyte than for the tracer; (b) contacting one end of the strip with a test soln. contg. the sample and the labelled reagent (9); (c) allowing the test soln. to migrate along the strip under capillary action, so that the labelled reagent binds to the tracer and the tracer is displaced from the antibody by the analyte; (d) washing the strip; (e) contacting the strip with a developer soln. contg. a signal-producing system capable of producing a detectable signal in the presence of the label; and (f) comparing the signal with standards. Also claimed is an assay as above comprising (a) binding a tracer to the antibody, where the tracer is an analyte analogue which is linked to a dye or is capable of binding a dye present in the test soln., and where the antibody has greater affinity for the analyte than for the tracer; (b) contacting one end of the strip with a test soln. contg. the sample (and opt. the dye); (c) allowing the test soln. to migrate along the strip under capillary action, so that the analyte displaces dye-labelled tracer from the antibody; and (d) comparing the signal produced by the dye with standards. Also claimed is a device for performing the first assay. The antibody is immobilised by covalent, adsorptive or hydrophobic/hydrophilic interaction. The strip is made of paper or a membrane material, opt. with a plastics support. The detectable signal is a colour change in the antibody zone, produced by a chemical or enzymatic reaction or by a coloured particle or molecular complex present in the labelled reagent. The test strip may have a second antibody zone downstream from the first, in which the immobilised antibody has greater affinity for the tracer than the first antibody or has affinity for another component of the reaction system. USE/ADVANTAGE - The assays may be used for determn. of low-molecular-wt. analytes, esp. pollutants (e.g. pesticides or their metabolites) in soil, water or air samples. Only one antibody is required; the strip has only one antibody zone (no capture zone is needed); the antibody is, in many cases, stabilised by the tracer, so strips with preformed antibody-tracer complex may be stored for long periods; no reactions take place in the test soln., so controlled conditions are not required; only the amt. of antibody needs to be fixed (other reagents may be used in excess).