Abstract <p>Immunoassay (IA) methods performed in the wells of a polystyrene microplate are the basis of diagnostic studies. In the “sandwich” IA, a fundamentally important initial stage is the immobilization of anchor antibodies in the well of the plate, designed for specific binding of a given antigen from a biological fluid. One of the very promising options for antigen-recognizing molecules are single-domain antibodies (nanoantibodies, Nbs). The use of Nbs as anchor antibodies is hampered by their low efficiency of functioning after passive adsorption in the well of the plate. The development of a new format and immobilization method in the case of Nbs are fundamentally important for overcoming this problem. This work describes the development of a new format of an anchor bispecific nanoantibody (anchor-Nb) to improve the efficiency of both passive adsorption of anchor-Nb and subsequent stages of immobilization and detection of the target antigen in the well of a polystyrene plate.</p>