How to determine the brightness of a fluorescent molecule?
Posted August 5, 2019
The brightness of a fluorescent molecule depends on two factors:
- Extinction Coefficient (ε) - how strongly a fluorescent molecule absorbs light at a particular wavelength.
- Fluorescence Quantum Yield (Φ) - how efficiently the absorbed light is converted into emitted light.
To calculate a fluorescent molecules 'brightness' use the following formula:
Brightness = Extinction Coefficient (ε) x Fluorescence Quantum Yield (Φ)
For example, let's use the above formula to compare the practical brightness of Phycoerythrin (PE), Allophycocyanin (APC) and Cy5.
- PE = 1,960,000 cm-1M-1 x 0.84 = 1,646,400
- APC = 700,000 cm-1M-1 x 0.68 = 476,000
- Cy5 = 250,000 cm-1M-1 x .20 = 50,000
Therefore, PE > APC > Cy5, in brightness
To view extinction coefficient or fluorescence quantum yield data for a particular molecule, use our: