Methods and kits are set out having improved selectivity and improved sensitivity for use in field and home immunoassays. A specifically binding biomaterial is attached to a macroextensive surface of a plastic strip or the like. A biological substance which is a specific binding partner to a binding site of the specifically binding biomaterial is attached to each of a plurality of synthetic particles. The particles are of a preselected size, refractive index, or the like to enhance their visibility in accordance with the Mie scattering phenomenon. Testing is by either contacting the particles with the strips to obtain adherence of the particles to the strips, or by exposing strips having the particles already adhering to them to a solution containing either the specifically binding biomaterial or the biological substance, whereby the particles adherence to the strip is eliminated. A quick and accurate pregnancy test is one result of the invention.

A stabilized radioimmunoassay product consisting of an antibody protein-bound to the cell wall of a selected bacterium whereby the antibody is irreversibly bound to the protein and remains specific for the antigen against which it was developed. The radioimmunoassay product is also characterized by the fact that the resultant complete product includes a phase of serum protein treatment to isolate the protein sites or other sites of nonspecific reactivity with the labelled antigen such that the non-specific binding of labelled antigen is significantly reduced. Also within the contemplation of the invention is the method of manufacturing the radioimmunoassay product which includes the initial phase of protein binding of the antibody to the selected bacterium and the subsequent serum treatment to isolate previously unutilized protein sites such that when said sites are subsequently exposed to labelled antigen it will be rejected. Further within the contemplation of the invention is the method of utilizing the aforesaid product to totally eliminate the necessity for the customary incubation stages necessitated by prior art radioimmunoassay techniques.