The amine-reactive Rhodamine Red™-X, succinimidyl ester can be used to create red-fluorescent bioconjugates with excitation/emission maxima ∼560/580 nm. This reactive dye contains an additional seven-atom aminohexanoyl spacer ('X') between the fluorophore and the succinimidyl ester group. This spacer helps to separate the fluorophore from its point of attachment, potentially reducing the interaction of the fluorophore with the biomolecule to which it is conjugated.