Digoxigenin (DIG) is a steroid found exclusively in the flowers and leaves of the plants Digitalis purpurea, Digitalis orientalis and Digitalis lanata (foxgloves), where it is attached to sugars, to form the glycosides (e.g. digoxin, lanatoside C). Digoxigenin is a hapten, a small molecule with high antigenicity, that is used in many molecular biology applications similarly to other popular haptens such as 2,4-Dinitrophenol, biotin, and fluorescein. Typically, digoxigenin is introduced chemically (conjugation) into biomolecules (proteins, nucleic acids) to be detected in further assays. Kd of the digoxigenin-antibody interaction has been estimated at ~12 nM (compare to Kd~0.1pM for the biotin-streptavidin interaction).