Cyanine dyes, a kind of polymethine dye derivatives with amidine ion vinylogies established at both ends of the chromophore conjugates between N-N atoms, belong to organic dyes. Typical cyanine dyes are formed when two nitrogen atoms and part of the polymethine chain are part of a heterocyclic nucleus. It is composed of two nitrogen atoms as heterocyclic nuclei, and has the advantages of stable fluorescence, chemical structure of polymethine bridged chain, high molar absorption coefficient and high fluorescence quantum yield. According to the type of molecular structure, it is divided into straight chain, bridged chain, cyclobutenedione, gram ketone, etc. For labeling biomolecules such as DNA and proteins, the more common cyanine dyes are CY3, CY5, CY7 and Sulfo-CY3, sulfo-CY5, sulfo-CY7.