SY-9 (QSY®-9 equivalent) is a more hydrophilic version of the popular SY-7 dark quencher (QSY®-7 equivalent). This nonfluorescent acceptor dye is often used for the preparation of peptide FRET probes. A broad and intense quenching range from 500-600 nm makes it useful as an acceptor in fluorescence resonance energy transfer (FRET) applications in conjunction with dyes emitting at 500 nm to 600 nm, such as Fluorescein, Oregon Green, Carboxyrhodamine 110 (Rhodamine Green), Alexa Fluor® 488, 532, 546, 555, 568, Cy3, TAMRA and ROX dyes.
The NHS ester (or succinimidyl ester) is the most popular amine reactive group for labeling with the primary amines of proteins (Lys), amine-modified oligonucleotides, and other amine-containing molecules. The labeling occurs most efficiently at pH 7-9 and forms a stable, covalent amide bond.