The efficiency of light emission–a key parameter determining fluorophore brightness and FRET sensitivity.
Donor quantum yield directly affects the Forster radiusLoading... through the equation R0 (ΦD)^(1/6). Higher donor quantum yield extends FRET range, enabling detection of interactions at slightly larger distances.
The ATTO488 donor used in QF-ProLoading... has quantum yield ~0.80 in aqueous solution, among the highest for green-emitting dyes. This contributes to the 5.83 nm Forster radius with Alexa594 acceptor.
What It Means: Quantum yield is the percentage of absorbed light that gets re-emitted as fluorescence. High quantum yield = bright fluorophore.
Why It Matters: For FRET, you need enough signal to detect. High quantum yield fluorophores provide better sensitivity, especially important when target proteins are sparse.
When a fluorophoreLoading... absorbs a photon, the excited electron can return to ground state through several pathways:
Fluorescence: Photon emission (what we detect)
Non-radiative decay: Heat dissipation (reduces QY)
FRETLoading...: Energy transfer to acceptor (the signal we measure)
High quantum yield means less non-radiative decay, leaving more energy available for either fluorescence or FRET.
Not All Energy Becomes Light: Excited molecules can release energy as fluorescence, heat, or through FRET. When FRET increases, fluorescence decreases—this is how we detect interaction.
The Balance: Good donor fluorophores have high intrinsic quantum yield, making the FRET-induced decrease easy to detect.
