Importance

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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. This value is compared with one or more corresponding values obtained in the same way using one or more standard liquid samples of known analyte concentration. An analytical device suitable for use in such a method comprises an extended solid substrate (20) bearing at a plurality of spaced-apart locations (21) a plurality of different receptors (22) each having binding sites on their molecule for an analyte, the receptor at any one location having binding sites specific for an analyte different from the analyte for which the receptor at one or more other locations has specific binding sites, each of the receptors being optionally labelled with a marker. This device can be used as part of a kit for the method.

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First Claim