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Cyanines have been used for many years as dyes, for example in photographic emulsions. Cyanine dyes began to be used widely as labels for nucleic acids in the early 1990s, when Cy3, Cy5 and Cy7 were made commercially available as succinimidyl esters (by Molecular Probes, Inc., now part of Life Technologies). These Cy dyes were different from previous cyanine dyes in that they contain sulfonate groups, which makes the Cy dyes soluble in water (and also reduce fluorescence-quenching which can arise from dye–dye interactions). Since their introduction the Cy dyes have found widespread use in DNA and RNA labelling.
The Quasar® dyes, manufactured and sold by Biosearch Technologues, are replacements for the Cy dyes. The Quasar dyes are chemically very similar to the Cy dyes (). As such, the properties of the Quasar dyes are practically identical to those of the Cy dyes.
Some physical properties of the Quasar dyes are compared with those of the Cy dyes in Table 1.
Table 1 ⎪ Common fluorescent dyes; their associated wavelengths of absorption (excitation) and emission, and colours
| Name | λmax / nm (absorption) | λmax / nm (emission) | Colour | E at λmax | Φ | τ / ns |
|---|---|---|---|---|---|---|
| Cy3 | 550 | 570 | Dark pink | 136 000 | 0.15 | - |
| Cy3.5 | 591 | 604 | - | 116 000 | 0.15 | < 0.3 |
| Cy3b | 558 | 572 | - | 130 000 | 0.67 | 2.8 |
| Cy5 | 649 | 670 | Blue | 250 000 | 0.3 | - |
| Cy5.5 | 675 | 695 | Blue | 209,000 | 0.3 | - |
| Quasar 570 | 548 | 566 | Dark pink | 115 000 | - | - |
| Quasar 670 | 647 | 670 | Blue | 187 000 | - | - |
| Quasar 705 | 690 | 705 | Blue | 206 000 | - | - |
Our free online Nucleic Acids Book contains information on all aspects of nucleic acids chemistry and biology.
