The amine-reactive dansyl-X succinimidyl ester can be used to create environment sensitive probes with this lipophilic dye. 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.