Abstract: The invention relates to methods of detecting a target antigen by optical detection, isotopic detection, or detection by electron microscopy, comprising contacting a first or second antibody with at least one monovalent antibody that specifically binds said first or second antibody, wherein the monovalent antibody has one or more fluorescent label(s), chromophore label(s), isotope label(s), or metal label(s) attached to it. The invention also relates to complexes formed by the methods of the invention, kits for performing the method of the invention, monovalent antibodies useful for conducting the methods of the invention, as well as uses of the monovalent antibody according to the methods of the invention.