Cy5.5 (Cyanine 5.5)

Cyanine 5.5 (Cy5.5) is a far-red/near infra red (NIR) fluorescent dye that belongs to the Cyanine family of synthetic polymethine dyes. Cy5.5 is reactive, water-soluble, and has an absorbance maximum of 675 nm and an emission maximum of 694 nm. It is available as a phosphoramidite, and is used to fluorescently label oligonucleotides at either the 5' or 3' end, or internally. Cy5.5 plays a particularly important role in real-time PCR applications, being used as a reporter moiety in TaqMan probes (1), Scorpion primers (2) and Molecular Beacons (3). For such probes, Cy5.5 is most commonly paired with the dark quencher BHQ-3, as the two have excellent spectral overlap.

Cy5.5 can also be used to label DNA oligos for use as hybridization probes in other applications, such as Fluorescent In-Situ Hybridization (FISH).

Near Infrared Fluorophore Spectral Data & Quencher Selection Guide
Fluorophore Name	Excitation Max, nm +/-10	Emission Max, nm +/-10	Extinction Coefficient*	Color**	Quencher
Cy5	650	665	250,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
IRDye 650 NHS	650	665	230,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
AZ647 NHS	655	680	191,800	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
Cy5.5	684	710	198,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
IRDye 700 NHS	684	710	288,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
Cy7 NHS	740	773	199,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
IRDye 750 NHS	756	776	260,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
cy7.5 NHS	788	808	223,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
IRDye 800 NHS	795	819	240,000	Human vision is insensitive to light beyond ~650 nm.	BBQ-650 λ (max) = 650nm Range = 550-750 nm
* Extinction coefficient at λ (max) in cm-1M-1. ** Typical emission color seen through the eyepiece of a conventional fluorescence microscope with appropriate filters. Near-IR region. Human vision is insensitive to light beyond ~650 nm; it is not possible to view near-IR fluorescent dyes. Click here for a list of fluorophores.
Click here for list of quenchers.

References
1. Livak, K.J., Flood, S.J.A., Marmaro, J., Giusti, W., Deetz, K. Oligonucleotides with fluorescent dyes at opposite ends provide a quenched probe system useful for detecting PCR product and nucleic acid hybridization.PCR Methods Appl. (1995), 4: 1-6.
2. Thelwell, N., Millington, S., Solinas, A., Booth, J., Brown, T. Mode of action and application of Scorpion primers to mutation detection. Nucleic Acids Res. (2000), 28: 3752-3761.
3. Tyagi, S., Kramer, F.R. Molecular beacons: probes that fluoresce upon hybridization. Nat. Biotechnol. (1996), 14: 303-308.
4. Stoecker, K., Dorninger, C., Daims, H., Wagner, M. Double Labeling of Oligonucleotide Probes for Fluorescence In Situ Hybridization (DOPE-FISH) Improves Signal Intensity and Increases rRNA Accessibility. Appl. Environ. Microb.. (2010), 76: 922-926.
- Cy5.5 (Cyanine 5.5)