Enzyme-Linked Immunosorbent Assay (ELISA) is used mainly to detect and quantify proteins, antibodies, peptides, or hormones in a sample. In ELISA, antigens are immobilized on a solid support, either coated directly or through specific capture antibodies. Primary detection antibodies are then applied, forming a complex with the antigen. If conjugated with an enzyme, the detection antibody can directly be used to quantify the antigen, or can itself be quantified by another enzyme-conjugated secondary antibody. The method chosen depends on which target you are investigating.