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Abstract: A ubiquitous observation in crowded cell membranes is that moleculartransport does not follow Fickian diffusion but exhibits subdiffusion. Themicroscopic origin of such a behaviour is not understood and highly debated.Here we discuss the spatio-temporal dynamics for two models of subdiffusion:fractional Brownian motion and hindered motion due to immobile obstacles. Weshow that the different microscopic mechanisms can be distinguished usingfluorescence correlation spectroscopy FCS by systematic variation of theconfocal detection area. We provide a theoretical framework for space-resolvedFCS by generalising FCS theory beyond the common assumption of spatiallyGaussian transport. We derive a master formula for the FCS autocorrelationfunction, from which it is evident that the beam waist of an FCS experiment isa similarly important parameter as the wavenumber of scattering experiments.These results lead to scaling properties of the FCS correlation for bothmodels, which are tested by in silico experiments. Further, our scalingprediction is compatible with the FCS half-value times reported by Wawreziniecket al. Biophys. J. 89, 4029 2005 for in vivo experiments on a transmembraneprotein.



Author: Felix Höfling, Karl-Ulrich Bamberg, Thomas Franosch

Source: https://arxiv.org/



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