Biocytin is a conjugate of biotin and lysine known formally as ɛ-N-(d-biotinyl)-L-lysine. The addition of lysine to biotin increases the chain length extending from biotin, allowing the synthesis of medium-chain reagents. It also provides terminal carboxyl and amino groups for derivatization or conjugation to proteins and other molecules. Covalent linking reactions typically involve carbodiimide or NHS-ester crosslinking chemistries. Biocytin is also used as an anterograde, retrograde, or intracellular neuroanatomical tracer that is fixable with aldehyde-based fixatives.1,2,3 For this and other applications, biocytin is detected with avidin or streptavidin probes.WARNING This product is not for human or veterinary use.