FRAP is an optical technique that has been broadly adopted in the bioscience community to quantify two dimension lateral diffusion rates of fluorescently labeled molecules in a thin film layer.
The physics and math can be best understood by the following illustration:
FRAP light path
❶ A pre-bleached sample image is taken as the baseline fluorescence intensity.
❷ The sample is photo-bleached by the laser.
❸ The intensity within this bleached spot is monitored as the bleached molecules diffuse out and fresh molecules diffuse in.
❹ Full recovery after bleaching.
The normalized fluorescence intensity versus time can be plotted and analyzed to retrieve two diffusion-related characteristics:
Mobile fraction: The value at which the intensity curve asymptotically settles.
Diffusion rate: Proportional to the slope at the curve starting point.
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