– 6-CR110, SE [6-Carboxyrhodamine 110, succinimidyl ester]*Single isomer* is a Fluorescein for peptide and oligonucleotide labeling. Compared to fluorescein labeling reagents such as FITC and FAM, CR110 reagents give more photostable and pH-independent bioconjugates that have the absorption maximum around the preferred 488 nm excitation wavelength. They are photostable alternative reagents superior to FITC and FAM.