  Fluorescence recovery after photobleaching (FRAP) measurements offer an
important tool for analyzing diffusion and binding processes. Confocal scanning
laser microscopes that are used in FRAP experiments bleach regions with a
radially Gaussian distributed profile. Previous attempts to derive analytical
expressions in the case of processes governed by fast diffusion have overlooked
the characteristics of the instruments used to perform FRAP measurements and
therefore led to approximating solutions. In the present paper, bleaching laser
beam characteristics are incorporated into an improved model to provide a more
rigorous and accurate method. The proposed model simulates binding inside
bounded regions, and it leads to FRAP curves that depend on the on and off
rates that can be employed to determine the rate constants. It can be used in
conjunction with experimental data acquired with confocal scanning laser
microscopes to investigate the biophysical properties of proteins in living
cells. The model aims to improve the accuracy when determining rate constants
by taking into account amore realistic scenario of the light-matter
interaction.
