Abstract: The invention relates to an immunoassay for the simultaneous immunochemical determination of an analyte (antigen) and a treatment antibody targeting the analyte in samples (recovery immunoassay). The inventive immunoassay comprises an optionally marked catcher antibody bound to a surface, a marked treatment antibody, or a marked antibody which has the same binding epitope as the treatment body, an antigen that binds to the catcher antibody and the treatment antibody in the region of various epitopes, and in this way forms an immunochemical sandwich, a solution of the unmarked treatment antibody of a known concentration, and an antigen solution to be added to the samples. The invention can be applied to the fields of medical diagnosis, treatment control and pharmacological research.

Abstract: The invention relates to surfaces coated with streptavidin and avidin for use in immunoassays, wherein the surfaces comprise a layer of streptavidin and avidin which are bonded on a surface of a solid supporting material through a biotinylated adhering agent.