A conjugated antibody is an antibody that has been attached to a specific tag or substrate such as an enzyme, inorganic compound, or toxin. It is also known as a labeled, tagged, or loaded antibody. Conjugated antibodies are used in several immunoassay techniques to isolate and purify a protein of interest from a complex protein mixture, usually cells and tissues or sometimes whole organisms.

Horseradish peroxidase (HRP) is the most common enzyme that’s used to conjugate antibodies. Antibodies may also be conjugated with fluorescent molecules such as APC, PE, FITC, and PerCP.