Cy®5 dye is a bright, far-red-fluorescent dye with excitation ideally suited for the 633 nm or 647 nm laser lines. A significant advantage to using long wavelength dyes such as Cy®5 dye or Alexa Fluor® 647 dye over other fluorophores is the low autofluorescence of biological specimens in this region of the spectrum.
The Cy®5 fluorophore is also the basis for the lipophilic neuronal and long-term DiD cell tracing reagents, which append alkyl tails (≥12 carbons) onto the core fluorophore.