Mobility of proteins in highly hydrated polyelectrolyte multilayer films.

The lateral diffusion of a protein (human serum albumin labeled with fluorescein isothiocyanate) within a highly hydrated polyelectrolyte film is studied. The film is built up with poly(l-lysine) as polycation and hyaluronate as polyanion. Fluorescence recovery after photobleaching is used to evaluate the mobility of the labeled protein. Spatial Fourier transformation is applied to the fluorescence intensity recorded at various times after bleaching of a narrow rectangular area within an image representative of the film. This approach necessitates no hypothesis on the intensity distribution at the end of the bleaching provided that the bleach has not appreciably changed the concentration ratios of the different diffusing species. Furthermore, under the hypothesis that molecules move according to Fick’s law, we represent the Fourier transform by a weighted sum of exponentials each containing another diffusion coefficient and evaluate the proportion attached to each term of this sequence using the simulated...