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Molecular FRET Reference Distance Point

Calculate ideal single-distance Förster transfer efficiency using an explicit positive Förster radius and sixth-power distance law.

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Description

Calculate an ideal single-pair FRET distance-efficiency term.

Biophysical scalar models require explicit signal, concentration, temperature, energy and geometric conventions. Effective concentration differs from dimensionless activity, a single displacement differs from mean-square displacement, and a fluorescence yield ratio needs absorption and refractive-index corrections. Supplied model parameters do not establish that the model applies to an experiment.

Calculate an ideal single-pair FRET distance-efficiency term.

When to use this tool

Use Molecular FRET Reference Distance Point when you already have distance, forsterRadius and need to calculate an ideal single-pair FRET distance-efficiency term.

How to use the tool and how it works

  1. Enter distance, forsterRadius. Use the units and conventions below.
  2. Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
  3. Read transferEfficiency. Use the output convention below.

Require distance>=0 and forsterRadius positive/finite; return 1/(1+(distance/radius)^6).1

The Förster distance dependence involves an inverse-sixth-power transfer relation. The supplied reference radius incorporates model assumptions about the fluorophore pair and environment; this helper does not infer them.2

Input fieldMeaning and unitsAccepted input
distanceDistanceRequired. Finite number; minimum 0.
forsterRadiusPositive supplied distance at which the model efficiency is 0.5; same unit as distance.Required. Finite number; strictly above 0.
Output fieldInterpretationReturned shape
transferEfficiency1/(1+(distance/forsterRadius)^6) under the supplied Förster model.Required. Finite number.
json
{
  "input": {
    "distance": 5,
    "forsterRadius": 5
  },
  "output": {
    "transferEfficiency": 0.5
  }
}

Limitations and assumptions

  • Lengths must match and radius/orientation assumptions are supplied. No FRET signal, distance distribution, fluorophore behavior or actual efficiency is measured; large ratios can numerically saturate to zero.
  • Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
  • Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Use the complete physical model, calibrated measurements and uncertainty analysis. Check reference states, photon-signal bases, diffusion assumptions and binding-constant conventions before interpreting local contributions as physical measurements.

References

  1. Calculation and input contract: biophysics/molecular-fret-reference-distance-point — tool.io

  2. Energy transfer: a spectroscopic ruler (1967) — Lubert Stryer and Richard P. Haugland

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