HiLyte Fluor™ 680-streptavidin conjugate has been optimized in fluorophore/protein labeling ratio to ensure high fluorescent signal and uncompromised streptavidin function. The fluorescence of HiLyte Fluor™ 680 is only slightly red-shifted compared to those of Cy5.5 dyes, resulting in an optimal match to filters designed for Cy5.5 dyes. Fluorescence emission of HiLyte Fluor™ 680 is well separated from that of other commonly used red fluorophores, such as TAMRA, R-phycoerythrin and HiLyte Fluor™ 647 dyes, making it ideal for three- and four-color labeling. The fluorescence signal of HiLyte Fluor™ 680-conjugate can be observed at 699 nm with the excitation at 678 nm.