Green fluorescent dye for the labeling of primary amines. Comprising fluorescein, with a commonly used fluorophore, the hexanoic spacer that separates the fluorophore from the molecule to which it is conjugated and makes the NHS ester group more accessible to biopolymers for conjugation. Excitation maximum = 494 nm; emission maximum = 520 nm, extinction coefficient: 74,000 cm-1M-1. Purity 90%. MW (observed): 586.55