Cyanine 3.5 (Cy3.5 NHS ester) chloride, a red fluorescent dye and reactive Cy3.5 fluorophore analog, is utilized for the labeling of amino groups in peptides, proteins, and oligonucleotides. It exhibits an excitation wavelength (λ ex) of 591 nm and an emission wavelength (λ em) of 604 nm. [1] [2]