Characterizing anomalous diffusion in crowded polymer solutions and gels over five decades in time with variable-lengthscale fluorescence correlation spectroscopy
| Autor: | Daniel S. Banks, Robert D. Peters, Felix Höfling, Cécile Fradin, Charmaine Tressler |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: |
0301 basic medicine
Physics Molecular diffusion Anomalous diffusion FOS: Physical sciences Fluorescence correlation spectroscopy General Chemistry Condensed Matter - Soft Condensed Matter Condensed Matter Physics 01 natural sciences Fick's laws of diffusion Molecular physics Condensed Matter::Soft Condensed Matter 03 medical and health sciences 030104 developmental biology Diffusion process Orders of magnitude (time) Biological Physics (physics.bio-ph) 0103 physical sciences Soft Condensed Matter (cond-mat.soft) Physics - Biological Physics Diffusion (business) 010306 general physics Brownian motion |
| Popis: | The diffusion of macromolecules in cells and in complex fluids is often found to deviate from simple Fickian diffusion. One explanation offered for this behavior is that molecular crowding renders diffusion anomalous, where the mean-squared displacement of the particles scales as $\langle r^2 \rangle \propto t^{\alpha}$ with $\alpha < 1$. Unfortunately, methods such as fluorescence correlation spectroscopy (FCS) or fluorescence recovery after photobleaching (FRAP) probe diffusion only over a narrow range of lengthscales and cannot directly test the dependence of the mean-squared displacement (MSD) on time. Here we show that variable-lengthscale FCS (VLS-FCS), where the volume of observation is varied over several orders of magnitude, combined with a numerical inversion procedure of the correlation data, allows retrieving the MSD for up to five decades in time, bridging the gap between diffusion experiments performed at different lengthscales. In addition, we show that VLS-FCS provides a way to assess whether the propagator associated with the diffusion is Gaussian or non-Gaussian. We used VLS-FCS to investigate two systems where anomalous diffusion had been previously reported. In the case of dense cross-linked agarose gels, the measured MSD confirmed that the diffusion of small beads was anomalous at short lengthscales, with a cross-over to simple diffusion around $\approx 1~\mu$m, consistent with a caged diffusion process. On the other hand, for solutions crowded with marginally entangled dextran molecules, we uncovered an apparent discrepancy between the MSD, found to be linear, and the propagators at short lengthscales, found to be non-Gaussian. These contradicting features call to mind the "anomalous, yet Brownian" diffusion observed in several biological systems, and the recently proposed "diffusing diffusivity" model. |
| Databáze: | OpenAIRE |
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