Journal of Radioanalytical and Nuclear Chemistry, Articles, VoL 102, No. 2 (1986) 429-434 A SOLID PHASE RADIOIMMUNOASSAY FOR TRIIODOTHYRONINE USING ANTIBODY-IMMOBILIZED SERUM ALBUMIN MICROSPHERES M. R. A. PILLAI, J. H. GUFI~, R. S. MANI ISOPHARM, Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Turbhe Complex, New Bombay 400 705 (lndiaj (Received March 19, 1986) A solid phase radioimmunoassay for triiodothyronine (T3) has been developed using antibody-immobilized serum albumin microspheres. Antibody albumin mictosphetes were prepared using a "spinning disc aerosol generator". The low density of the antibody-albumin mierospheres gives greater mobility for the particles there by ensuring better kinetics to the antigen-antibody reaction. The assay has a single incubation of one hour at 37 ~ and the separation of the antigen-antibody complex is accomplishedby centrifugation. The sensi- tivity of this assay is 0.3 ng/cma and has a range of 0.3-4 ng/ern a . Introduction Solid-phase radioimmunoassays in which the antibodies are physically adsorbed to polystyrene tubes, beads disc or chemically coupled to insoluble polymers like cellulose, sephadex, sepharose, etc., are in wide use due to their simplicity in separation of the antibody bound antigen from the free antigen J,2 Assays based on physically adsorbed antibodies are found to be imprecise, while the chemically coupled antibody based assays are superior with respect to precision and accuracy. However, chemical coupling of the antibody is generally accomplished using cyanogen bromide activation method. Toxicity of cyanogen bromide necessitates the use of elaborate handling facilities during the coupling procedure. Here we report a simple and novel alternative for the preparation of solid-phase antibodies. In this procedure antibody immobilized serum albumin microspheres were prepared in a 'spinning disc aerosol generator' and used in the assays . Experimental Materials 3, 3', 5-Triiodothyronine and bovine serum albumin (BSA) were purchased from Sigma Chemical Company, USA. Elsevier Sequoia S. A., Lausanne Akaddmiai Ktad6, Budapest