Universal Black 2 Quencher (UBQ-2, Black Hole Quencher®-2 (BHQ®-2) equivalent) is a dark quencher with no native emission due to the polyaromatic-azo backbone. This nonfluorescent acceptor is often the quencher of choice for qPCR probes and for other fluorescence-quenched probe applications. A broad and intense quenching range from 560-670 nm makes it useful as an acceptor in fluorescence resonance energy transfer (FRET) applications in conjunction with orange to far-red emitting dyes such as Cy3, Cy5, ROX, Texas Red, Alexa Fluor® 546, 555, 594, 633, 647, and IRDye® 650.
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.