Abstract: An assay method and kit in which particles bearing a first reagent binding pair member (e.g., anti-digoxin antibody) react with a sample such that analyte binding pair member (e.g., digoxin) binds to the first reagent binding pair member. The reaction mixture is then passed through a filter or membrane or pore size sufficient to allow particles to pass through. A second reagent binding pair member (e.g., digoxin-albumin conjugate) is immobilized on the filter or membrane to trap preferentially either particles which have bound analyte binding pair members or particles which have not, leaving the other class of particles to pass through the filter for detection by resistive pulse techniques, by light absorbence or scattering, by enzymatic read-out (when the particles are enzyme-labeled) or otherwise.

Abstract: Competitive or inhibition assays are disclosed in which sample (e.g., containing target antigen), a reagent containing first particles (e.g., antibody-coated light particles) and a reagent containing second particles (e.g., antigen coated heavy particles) are reacted in a centrifugal field. Differential migration of first particles, of second particles and of first particles linked to second particles leaves a concentration of particles at a locus in solution after a time, which concentration is a function of the analyte concentration in the sample.

Abstract: A suspension of particles such as carboxylated polystyrene latex particles are coated (as by carbodiimide coupling) with an antigen (such as chemically modified Bovine Serum Albumin). The antigen-coated particles are incubated with a gamma-globulin to the antigen (such as can be produced by immunizing rabbits) under non-agglutinating conditions. The particles having antigen/gamma-globulin immune complexes are recovered and resuspended to form a diagnostic reagent which agglutinates when mixed with human serum containing Rheumatoid Factor.