Cyanine dyes are a class of fluorescent dyes. They are used to label amine groups on peptides, antibodies, oligonucleotides, or nucleic acids. Labeling is done for visualization and quantification purposes. Cyanine dyes are suitable for use in a wide range of fluorescence detection techniques including flow cytometry, microscopy, and fluorescence resonance energy transfer (FRET).

There are several different cyanine dyes. Each one differs with respect to their molecular structure, charge, and membrane permeability.