𝓃

Refractive index of the medium (1.33 is used for the table calculations)

κ²

Orientation factor (0.667 is used for the table calculations)

λmax_D

Excitation maximum of the donor (nm)

Δλ_em

Separation between emission maxima of the donor and acceptor (nm). FRET pairs with small emission seperation are difficult to use in practice due to overlapping emission.

QY_D

Quantum yield of the donor

ε_A

Extinction Coefficient of the acceptor (M^-1 cm^-1)

QY_A

Quantum yield of the acceptor. FRET acceptors with low quantum yield may provide very low dynamic range between low and high FRET conditions (unless you're doing FLIM and only looking at the lifetime of the donor).

J(λ)

Overlap integral of the donor emission and acceptor excitation spectra, where:

R₀

Förster radius: distance at which 50% FRET efficiency occurs (Å), where:

R₀×QY_A

Förster radius multiplied by the quantum yield of the acceptor. A useful indication of how large of an emission peak ratio change one might expect to see under high FRET vs. low FRET conditions

Helpful References

• Wu & Brand (1994). Resonance Energy Transfer: Methods and Applications. Analytical Biochem. 218(1)
• Bajar et al. (2016). A Guide to Fluorescent Protein FRET Pairs. Sensors 16(9)
• Mastop et al. (2017). Characterization of a spectrally diverse set of fluorescent proteins as FRET acceptors for mTurquoise2. Sci. Rep. 7(1)

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