For over 50 years, immunoassays have been used by physicians, biologists, and forensic scientists to diagnose disease, detect contamination, and to determine the origin of biological samples found at crime scenes. Immunoassays rely on the uniqueness of antibodies. Antibodies are typically produced by the immune system in response to antigens – bacteria, viruses, pollen, or anything that your body perceives as foreign. Our bodies are capable of producing billions of different protective proteins called antibodies, each one specific to a different antigen. When an antibody and an antigen are a match, they bind together – similar to a lock and key.