Cy3 Acid (also sold under Sulfo-Cyanine3 Acid) is a bright, water-soluble, and pH insensitive from pH 4 to pH 10 orange-fluorescent dye. Cy3 conjugates of antibodies, peptides, and proteins can be excited using the 532 nm or 555 nm laser line and visualized with TRITC (tetramethylrhodamine) filter sets. Cy3 conjugates give less background than TAMRA and most other commonly used fluorescent dyes.
The carboxylic acid of Cy3 dye is a reagent of choice for the preparation of custom activated esters that often are not commercially available. Examples of such activated esters include sulfo-NHS, TFP (2,3,5,6-Tetrafluorophenol), STP (4-Sulfo-2,3,5,6-Tetrafluorophenol, Sodium Salt). Another common application for non-activated carboxylic acid is peptide modification during solid phase synthesis, which usually requires in-situ activation with peptide coupling regents, for example HATU. Cy3 Acid is also often used for control experiments, and for calibration.