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Quantitative Metric

FRET Efficiency

The quantitative metric calculated from donor lifetime reduction–providing continuous numerical output that distinguishes interacting from non-interacting protein pairs with physics-based precision.

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Definition
FRETLoading... Efficiency (Ef) quantifies the proportion of energy transferred from donor to acceptor chromophoreLoading.... Calculated as Ef = [1 - (τDA/τD)] × 100, where τDA is donor lifetimeLoading... in presence of acceptor and τD is donor-only lifetime. A 4% threshold–corresponding to ~10 nm separation–provides a physics-based cutoff for true molecular interaction.
Video Segments
Fluorescence Lifetime & Why It Matters
Primary
QF-Pro Score: How FRET Efficiency Is Calculated
Primary
The 2.13% Clinical Cutoff
Primary
Interaction threshold
10 nm cutoff
Continuous variable
Not binary positive/negative
Lifetime-derived
Intensity-independent
Violet 3.0
Regulatory compatible
Quantitative endpoint

Lifetime-Based Measurement

In the iFRETLoading... and QF-ProLoading... platforms, FRET efficiency is calculated from fluorescence lifetime rather than intensity. This approach offers critical advantages for clinical applications:

Intensity-independent: Lifetime is an intrinsic property of the chromophore, unaffected by variations in excitation intensity, photobleaching, or sample thickness. This ensures reproducible measurements even in heterogeneous tissue samples.

Robust at low expression: Because lifetime measurements are ratiometric, they remain accurate even when absolute signal intensity is low–precisely the situation where expression-based assayLoading...s fail.

Simplified

How It's Calculated: FRET efficiency (E) is measured from the change in donor lifetime: E = 1 - (τDA/τD), where τDA is lifetime with acceptor and τD is lifetime without acceptor.

What It Tells You: Higher efficiency means closer distance. The percentage gives a quantitative, continuous measure—not just "interacting" or "not interacting" but how strongly.

Clinical Validation Data

  • MelanomaLoading... (176 patients): Higher median FRETLoading... efficiency correlated with improved overall survival (p=0.05). PD-L1 expression showed no correlation (p=0.87)
  • NSCLCLoading... (40 patients): FRET efficiency range 0.00%–29.90%. Patients with lowest 60% median efficiency showed significantly worsened survival on anti-PD-1 therapy (p=0.05)
  • Breast Cancer (230 TMAs): Akt/PKBLoading... activation measured by FRET efficiency (range 2.5%–6.0%) predicted disease-free and overall survival–where IHCLoading... intensity ratio failed

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