Fluorescent biocytin conjugates are cell-impermeant, fixable polar tracers with biotin and an aldehyde-fixable primary amine groups. Polar tracers are commonly used to investigate cell-cell and cell-liposome fusion as well as membrane permeability and transport through gap junctions or cell uptake during pinocytosis. CF® dyes are Biotium's line of next-generation fluorescent dyes with advantages in brightness, photostability, and conjugate specificity compared to other fluorescent dyes. • Green fluorescent CF®488A dye has excitation/emission at 490/515 nm. • Red fluorescent CF®568 dye has excitation/emission at 562/583 nm. • Deep-red fluorescent CF®594 dye has excitation/emission at 593/614 nm. • Far-red fluorescent CF®640R dye has excitation/emission at 642/662 nm.