Binding assay device

Claim 1

A test system for performing a binding assay for determining the presence or absence of analyte in a sample or the relative concentrations of two analytes in a sample, comprising: a) an absorbent material in the form of an elongate strip having a sample application zone upstream of a plurality of transverse reagent zones, wherein said reagent zones of said absorbent material comprise, at least an enzyme-labelled reagent zone which includes an enzyme-labelled species comprising an enzyme-labelled analyte or an enzyme-labelled reagent that binds to said analyte, such that in use, said enzyme-labelled species is caused to migrate through the strip by passage of a developing solution through the strip, and an indicator reagent zone which includes an immobilized reagent that, directly or indirectly, binds and thereby immobilizes said enzyme-labelled species in an amount dependent on the quantity of said analyte present in said sample; and b) a developing solution, wherein said developing solution comprises a signal-producing substrate for the enzyme that generates signal only in or downstream from said indicator reagent zone, wherein the signal-producing substrate is a single color-producing compound or a compound acting as a cofactor with a further compound or compounds to produce a signal in the presence of enzyme, wherein said any further compound or compounds are present in the developing solution; wherein said developing solution is initially in contact only with that portion of said absorbent material upstream from said indicator zone but in which ultimately, by capillary action, sequentially contacts all reagent zones of said absorbent material; wherein said enzyme-labelled species is mobilized in said developing solution but does not react with said signal producing substrate to produce color except at or downstream form said indicator reagent zone; and wherein said signal-producing substrate is transported by the developing solution slower than, said enzyme-labelled species.