CF® Dye Succinimidyl Esters (SE, also known as NHS esters) are amine-reactive fluorescent dyes. SE dyes are commonly used to label antibodies and other proteins on free amine groups, such as lysine residues. CF® dyes are Biotium's line of next-generation fluorescent dyes with advantages in brightness, photostability, and conjugate specificity compared to other fluorescent dyes. Far-red fluorescent CF®633 dye has excitation/emission at 630/650 nm.