Antibodies, also known as immunoglobulins, are proteins produced by the immune system that are able to bind to specific molecules, known as antigens. There are several applications of antibodies in medicine, including: Diagnostics: Antibodies can be used to detect the presence of specific molecules in a sample, such as a virus or cancer marker. This is the principle behind many diagnostic tests, such as ELISA (enzyme-linked immunosorbent assay) and Western blot. Therapy: Antibodies can be used to treat certain conditions, such as cancer or autoimmune diseases. This is known as immunotherapy. For example, monoclonal antibodies (mAbs) can be used to target and block specific molecules on cancer cells, or to stimulate the immune system to attack them. Research: Antibodies can be used to study the function and localization of specific molecules in cells and tissues. This is commonly done in the fields of cell biology and biochemistry. Antibodies can also be used to purify specific protein from a mixture of proteins. This is commonly used in the field of protein purification. Antibodies are also used to detect the presence of certain pathogens like SARS-Cov-2 in COVID-19 tests. Antibody purification is the process of isolating a specific antibody from a mixture of proteins. This is typically done by using techniques such as protein purification, chromatography, or electrophoresis. The most common method is protein A or G affinity chromatography, which uses the binding of antibodies to a protein A or G magnetic beads. Other methods include protein A/G and protein L ion-exchange chromatography, and protein A/G and protein L HPLC. The purified antibody can then be used for various applications, such as ELISA, Western blotting, or as a therapeutic agent.