SY-21 NHS ester

Unit Size
Price (USD)
Cat.#: 1712-5
Unit size: 5 mg
in stock
Cat.#: 1712-25
Unit size: 25 mg
in stock
Cat.#: 1712-100
Unit size: 100 mg
in stock

SY-21NHS Ester (QSY®-21 succinimidyl ester equivalent) is a nonfluorescent acceptor dye often used for preparation of peptide and oligonucleotide FRET probes. A broad and intense quenching range from 580 nm to 680 nm makes it useful as an acceptor in fluorescence resonance energy transfer (FRET) applications in conjunction with fluorescent dyes at 580 nm to 680 nm, such as Fluorescein, Alexa Fluor® 568, 594, 633, 647, TAMRA, ROX, Texas Red and Cy5.

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.

Primary amine
Abs maximum
661 nm
Extinction coefficient
90,000 cm-1M-1
Spectrally compatible dyes
Alexa Fluor® 568, 594, 633, 647, TAMRA, ROX, Texas Red, Cy5.
Molecular weight
Storage conditions
Shipping conditions
Ambient temperature


Enter only one — either volume or amount of protein to be labeled
Enter only one — either maximum concentration of DMSO or volume DMSO added to label

QSY® is a trademark of a registered trademark of Thermo Fisher Scientific.