Immunoassay system

A method of generating a visually-perceptible signal in a competitive immunoassay for the detection of a ligand in a liquid sample when said ligand is absent, comprising the steps:

• a) providing a fluid sample, a particulate dye having a ligand analog adsorbed thereon, and a membrane having a multiplicity of immobilized receptors thereon having binding sites specific for said ligand and ligand analog, said ligand analog being present in an amount equal to or greater than the number of binding sites available upon said immobilized receptors;
• b) contacting said fluid sample with said particulate dye having said ligand analog adsorbed thereon to produce a first admixture;
• and
• c) contacting said first admixture with said immobilized receptors such that said ligand analog is freely allowed to bind therewith.

A competitive immunoassay for detecting two dissimilar first and second ligands in a liquid sample suspected of containing one or both of said ligands, said immunoassay comprising:

• a) an elongate strip of plastic backing having proximal and distal ends;
• b) a first absorbent pad being designed and oriented to contact and absorb at least a portion of said fluid sample;
• c) a second absorbent pad;
• d) a first ligand analog formed upon said second absorbent pad, said first ligand analog being adsorbed upon a particulate dye and formulated to dissolve into said portion of said fluid sample when said second absorbent pad is contacted therewith;
• e) a second ligand analog formed upon said second absorbent pad, said second ligand analog being adsorbed upon a particulate dye and formulated to dissolve into said portion of said fluid sample when said second absorbent pad is contacted therewith;
• f) a porous membrane having a first zone of immobilized receptors formed thereon having binding sites formed thereon for said first ligand and said first ligand analog, and a second zone of immobilized receptors having binding sites formed thereon specific for said second ligand and said second ligand analog;
• and
• g) wherein said first absorbent pad, said second absorbent pad and said membrane are arranged adjacent to one another in a linear fashion upon said elongate strip of plastic backing, said first absorbent pad, second absorbent and membrane defining a path of migration of said fluid sample such that in use, said first and second ligand analog-particulate dye complexes are caused to migrate to and contact said first and second zones of immobilized receptors such that in the absence of first ligand in the fluid sample, said first ligand analog-dye complex freely binds to said binding sites and correspondingly produces a visually perceptible signal thereat, and in the absence of second ligand in the fluid sample, said second ligand analog-dye complex freely binds to said binding sites and correspondingly produces a visually perceptible signal thereat.