What are cyanine dyes?



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.

For applications to biotechnology, special cyanine dyes are synthesized from 2, 3, 5 or 7-methine structures with reactive groups on either one or both of the nitrogen ends so that they can be chemically linked to either nucleic acids or protein molecules. Labeling is done for visualization and quantification purposes. Biological applications include comparative genomic hybridization and gene chips, which are used in transcriptomics, and various studies in proteomics such as RNA localization,[7] molecular interaction studies by fluorescence resonance energy transfer (FRET) and fluorescent immunoassays .

Cyanine dyes are available with different modifications such as methyl, ethyl or butyl substituents, carboxyl, acetylmethoxy, and sulfo groups which alter their hydrophilicity.

Cyanine3 (CY3), Sulfo-CY3
It is a kind of anthocyanin dye that emits orange light, also called trimethyl cyanine dye, generally refers to fat-soluble CY3, which is difficult to dissolve in water, and the water-phase labeling needs to be co-dissolved in organic solvents, and another is sulfonated CY3 , it has better water solubility, brighter and more stable fluorescence, and can be used to label active groups, proteins, sugars, polypeptides, antibodies, etc.

Cyanine5 (CY5), Sulfo-CY5
It is a red fluorescent anthocyanin dye, also called Wujiachuan cyanine dye, and is also a common fluorescent labeling compound. Soluble in organic co-solvents (such as DMF or DMSO), it is more sensitive than CY3, and can be used to label amino groups of peptides, proteins and oligonucleotides. Sulfonated CY5 (water-soluble CY5) can label various functional groups in the aqueous phase and is suitable for labeling organic solvent-sensitive biomolecules.

Cyanine7 (CY7), Sulfo-CY7
It is a near-infrared cyanine fluorescent dye, also called heptacyanine dye. It has weak background fluorescence and strong penetrability in blood, body fluids and tissues of the body, so it is often used in in vivo imaging of small animals. The light it emits is invisible to the naked eye, so it can only be identified with some fluorescent instruments. Sulfonated CY7 (Sulfo-CY7) is a water-soluble biomolecule that can label various reactive groups and some organic solvent-sensitive biomolecules.