QSY 21 has a wide - ranging and intense absorption with a peak at 661 nanometers. It emits no detectable fluorescence, which makes it highly useful as an acceptor in Fluorescence Resonance Energy Transfer (FRET) applications. As a commonly - used long - wavelength quencher, it can be optimally paired with fluorescent dyes such as Cy5, Alexa Fluor 647, iFluor 647, or other dyes with similar spectra.

Providing storage is as stated on the product vial and the vial is kept tightly sealed, the product can be stored for up to 24 months.
Wherever possible, you should prepare and use solutions on the same day. However, if you need to make up stock solutions in advance, we recommend that you store the solution as aliquots in tightly sealed vials at -20°C. Generally, these will be useable for up to one month. Before use, and prior to opening the vial we recommend that you allow your product to equilibrate to room temperature for at least 1 hour.