Biotin, also known as Vitamin H or Coenzyme R, is a water-soluble B-complex vitamin (vitamin B7) discovered by Bateman in 1916. It is composed of a ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a coenzyme in the synthesis of fatty acids, isoleucine, and valine, and it plays a role in gluconeogenesis.

The high affinity (10-15 M-1) between the glycoprotein avidin and biotin has been exploied for a variety of bioanalytical applications such as affinity chromatography, localization, immunodiagnostics, and detection of nucleic acids. A key feature of the avidin-biotin technology requires the prior covalent modification of the biological probe or matrix with biotinylated derivatives. Thus, a number of biotinylating reagents have been reported. For example, to name a few, biotinyl-p-nitrophenyl and biotin N-hydroxysuccinimide esters, biotin and biocytin hydrazides, photobiotin, and 3-(N-maleimidopropionyl)biocytin.