Answer:
protein
Explanation:
For instance, in some Enzyme-linked immunosorbent assay (ELISA) kits, the wells of the microplates are coated with antigens while in some others, the wells of the microplates are coated with antibodies. When the wells are coated with antigens for instance, the antigens will naturally elicit a reaction with specific protein/antibodies in the sample and hence makes it possible for the protein/antibody to be detected at specific wavelength using a microplate reader.
It should be noted that Antigens and Antibodies are both proteins and hence the interaction experienced in these processes are a form of protein-protein interaction.
Western blotting (done after a SDS-PAGE electrophoresis) and immunofluorescence light microscopy (used on cells and tissues) are both used to analyze and identify proteins also.
