are detectable because they either emit radiation, produce a color change in a solution, fluoresce under light, or can be induced to emit light. History Rosalyn Sussman Yalow and Solomon Berson are credited with the development of the first immunoassays in the 1950s. Yalow accepted the Nobel Prize for her work in immunoassays in 1977, becoming the second American woman to have won the award. Immunoassays became considerably simpler to perform and more popular when techniques for chemically linked enzymes to antibodies were demonstrated in the late 1960s. In 1983, Professor Anthony Campbell at Cardiff University replaced radioactive iodine used in immunoassay with an acridinium ester that makes its own light: chemiluminescence. This type of immunoassay is now used in around 100 million clinical tests every year worldwide, enabling clinicians to measure a wide range of proteins, pathogens and other molecules in blood samples. By 2012, the commercial immunoassay industry earned and was thought to have prospects of slow annual growth in the 2 to 3 percent range. Labels Immunoassays employ a variety of different labels to allow for detection of antibodies and antigens. Labels are typically chemically linked or conjugated to the desired antibody or antigen. Enzymes Possibly one of the most popular labels to use in immunoassays is enzymes. Immunoassays which employ enzymes are referred to as enzyme immunoassays (EIAs), of which enzyme-linked immunosorbent assays (ELISAs) and enzyme multiplied immunoassay technique (EMIT) are the most common types. Enzymes used in ELISAs include horseradish peroxidase (HRP), alkaline phosphatase (AP) or glucose oxidase. These enzymes allow for detection often because they produce an observable color change in the presence of certain reagents. In some cases these enzymes are exposed to reagents which cause them to produce light or chemiluminescence. Radioactive isotopes Radioactive isotopes can be incorporated into immunoassay reagents to produce a radioimmunoassay (RIA). Radioactivity emitted by bound antibody-antigen complexes can be easily detected using conventional methods. RIAs were some of the earliest immunoassays developed, but have fallen out of favor largely due to the difficulty and potential dangers presented by working with radioactivity. DNA reporters A newer approach to immunoassays involves combining real-time quantitative polymerase chain reaction (RT qPCR) and traditional immunoassay techniques. Called real-time immunoquantitative PCR (iqPCR) the label used in these assays is a DNA probe. Fluorogenic reporters Fluorogenic reporters like phycoerythrin are used in a number of modern immunoassays. Protein microarrays are a type of immunoassay