Pixel-based analysis of FRAP data with a general initial bleaching profile.

Area of Science:

• Materials Science
• Polymer Science
• Biophysics

Background:

• Fluorescence Recovery After Photobleaching (FRAP) is a key technique for measuring molecular diffusion.
• Previous methods, like the Gaussian profile method, rely on assumptions about the initial photobleaching profile.
• Confocal Laser Scanning Microscopy (CLSM) is commonly used for FRAP experiments.

Purpose of the Study:

• To introduce an extended maximum likelihood framework (Monotone profile method) for diffusion coefficient estimation.
• To accommodate general, non-decreasing initial bleaching profiles and Poisson noise.
• To compare the accuracy and limitations of the Monotone and Gaussian profile methods.

Main Methods:

• Developed the Monotone profile method within a pixel-based maximum likelihood framework.
• Applied both Monotone and Gaussian profile methods to FRAP data of swelling superabsorbent polymers (SAP).
• Validated results using NMR diffusometry and simulated data.

Main Results:

• The Monotone profile method demonstrated accuracy across various initial bleaching profiles (step-like to Gaussian).
• The Gaussian profile method showed sufficient accuracy for most profiles but underestimated diffusion for step-like profiles.
• The Monotone method is computationally intensive, while the Gaussian method is faster but less universally accurate.

Conclusions:

• The Monotone profile method offers improved accuracy for diffusion coefficient estimation in FRAP experiments.
• A diagnostic plot is provided to guide the selection between Gaussian and Monotone methods.
• Understanding initial bleaching profile characteristics is crucial for accurate diffusion measurements.