Binding assay device

Claim 1

A test system for performing a binding assay for determining the presence or absence of an analyte 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 an enzyme-labelled reagent zone includes an enzyme-labelled species, comprising either 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 wherein an indicator reagent zone 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 which 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 any of said 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, and wherein said signal-producing substrate is transported by the developing solution slower than said enzyme-labelled species either by addition to said absorbent material at least one compound that increases the attractive interaction between said absorbent material and said substrate relative to the attractive interaction between said absorbent material and said enzyme-labelled species or by provision of a substrate binding reagent zone which binds said substrate at a location upstream from said enzyme-labelled reagent zone, such that, in use, the substrate is prevented from passing through said binding reagent zone until said binding reagent zone is substantially saturated.