Abstract: Reagents for a liquid-phase immunodiagnostic assay (LIDA) method comprise a first enzyme; a second enzyme; a first agent which is capable of binding with an analyte to form a complex, the agent being attached to one of the first and second enzymes; and a complex-binding agent attached to the remaining enzyme, wherein the first enzyme is capable of interacting with a substrate for the first enzyme together with any necessary additional substrates for the first enzyme to produce a substrate for the second enzyme, and wherein the second enzyme is capable of interacting with the substrate produced by the first enzyme together with any necessary additional substrates, such that occurrence of the second of the interactions is detectable. The reagent optionally further comprises a scavenger substance capable of inactivating the substrate produced by the first enzyme.

Abstract: For the serodiagnosis of a fluid sample, it is particularly advantageous to use a device comprising (A) a supported, porous membrane wherein a first immunoreagent is bound so as to be capable of binding a foreign analyte and forming a complex when the foreign analyte is brought into contact therewith; and (B) a matrix which presents a first surface and an opposing second surface and which contains a second, labeled immunoreagent that is capable of binding the foreign analyte to form a labeled complex when the foreign analyte is sandwiched between the first immunoreagent and the second immunoreagent. In such a device, the first surface of the matrix is adjacent to a surface of the membrane, (ii) the matrix is wettable by or soluble in an aqueous fluid, and (iii) the second immunoreagent is mobilized when the matrix is wetted.