This Cy3 dye is the same molecule to GE's Cy3 bisNHS ester. It has two NHS groups that might give brighter signal on some proteins than the Cy3 mono NHS ester (#141 and #271). A variety of cyanine 3 (Cy3) dyes has been used to label biological molecules for fluorescence imaging and other fluorescence-based biochemical analysis. They are widely used for labeling peptides, proteins and oligos etc. Cy3 dyes have enhanced fluorescence upon binding to proteins. Cy3 NHS ester readily reacts with amino groups. Cy3 is the trademark of GE Healthcare.