1. What is Donor Lifetime with FRET?

The Donor Lifetime with FRET represents the fluorescence lifetime of a donor molecule in the presence of Förster Resonance Energy Transfer (FRET). It accounts for all de-excitation pathways including energy transfer to an acceptor molecule.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \zeta_{DA} \) — Donor lifetime with FRET (seconds)
• \( K_T \) — Rate of energy transfer (s^-1)
• \( K_r \) — Rate of radiative transitions (s^-1)
• \( K_{nr} \) — Rate of non radiative transitions (s^-1)

Explanation: The donor lifetime is inversely proportional to the sum of all de-excitation rates, including energy transfer to acceptors.

3. Importance of Donor Lifetime Calculation

Details: Calculating donor lifetime with FRET is crucial for understanding energy transfer efficiency, molecular interactions, and distance measurements in fluorescence spectroscopy and biological imaging.

4. Using the Calculator

Tips: Enter all rate values in s^-1. Ensure all values are non-negative. The sum of rates must be greater than zero for a valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is FRET efficiency?
A: FRET efficiency is the fraction of energy transferred from donor to acceptor, calculated as \( E = \frac{K_T}{K_T + K_r + K_{nr}} \).

Q2: How does donor lifetime change with FRET?
A: The presence of FRET shortens the donor lifetime due to the additional energy transfer pathway.

Q3: What are typical values for these rates?
A: Rates typically range from 10⁶ to 10⁹ s^-1, depending on the fluorophore and experimental conditions.

Q4: Can this calculator be used for time-resolved measurements?
A: Yes, the calculated lifetime is directly applicable to time-resolved fluorescence measurements.

Q5: What factors affect the rate of energy transfer?
A: The energy transfer rate depends on the donor-acceptor distance, spectral overlap, relative orientation, and the Förster radius.