Coupling of antibodies to magnetic particles for radioimmunoassay and immunoradiometric assay of hormones

Silanized magnetic particles have been developed by means of a number of different methods for coupling antibodies for use in radioimmunoassay (RIA) and immunoradiometric assay (IRMA) of thyroid related hormones. Coarse and fine iron oxide particles were prepared by use of chemical precipitation of ferrous chloride and ferric chloride in NaOH or NH4OH under different reaction conditions. Carbodiimide, glutaraldehyde, glutaric anhydride and spacer arms coupling methods were studied for immobilization of triiodothyronine (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) antibodies on magnetic particles, respectively. The effect of the magnetic particle preparation and the properties of the particles on the couplings was discussed. The influence of coupling conditions, such as reaction time, coupling media and pH, concentration of coupling reagent and coupling ratio of antibody and magnetic particles, on the preparation of magnetic particle antibodies and the assay performance was also investigated. A comparison of five types of magnetic particles from different sources for coupling TSH antibody for TSH IRMA application was made. Silanized magnetic particles and other types of particles showed comparable results. Five TSH antibodies, including two polyclonal and three monoclonal antibodies coupled to silanized magnetic particles respectively, were used in TSH IRMA. It was found that each of them and a commercial monoclonal TSH antibody as label formed good sandwich partners and gave a high signal to low levels of TSH. T3, T4 and TSH antibodies coupled to silanized magnetic particles have been used in total T3, total T4, blood spot total T4 RIA and TSH IRMA. The storage stability and reproducibility were satisfactory. These magnetic antibodies have also been employed for free T3, free T4 RIA and blood spot TSH IRMA, but some of the technical problems remained to be solved. 13 refs, 7 tabs