Method and apparatus for optically detecting presence of immunological components

An apparatus for visually detecting the presence of an analyte which is a member of an immunological pair (mip) in a liquid sample which comprises:

• a substrate having at least one flat surface for receiving a stepped layer;
• the stepped layer, coated onto said substrate with at least one step with flat surfaces parallel to the substrate flat surface wherein the reflectivity at a substrate-stepped layer interface is substantially the same as the reflectivity at the interface between the stepped layer and air;
• and,
• a detection zone in which a first mip is immobilized upon step surfaces of the stepped layer, the index of refraction of said immobilized first mip being substantially similar to the index of refraction of said stepped layer,
• whereby the presence of the analyte which is a second mip in the liquid sample is detected by wetting the detection zone with the liquid sample, and observing any color change in the detection zone resulting from an increased thickness of the at least one step caused by binding of the second mip to the first mip immobilized upon the at least one step.