Anomalous Colloidal Motion under Strong Confinement

Diffusion of biological macromolecules in the cytoplasm is a paradigm of colloidal diffusion in an environment characterized by a strong restriction of the accessible volume. This makes of the understanding of the physical rules governing colloidal diffusion under conditions mimicking the reduction in accessible volume occurring in the cell cytoplasm, a problem of a paramount importance. This work aims to study how the thermal motion of spherical colloidal beads in the inner cavity of giant unilamellar vesicles (GUVs) is modified by strong confinement conditions, and the viscoelastic character of the medium. Using single particle tracking, it is found that both the confinement and the environmental viscoelasticity lead to the emergence of anomalous motion pathways for colloidal microbeads encapsulated in the aqueous inner cavity of GUVs. This anomalous diffusion is strongly dependent on the ratio between the volume of the colloidal particle and that of the GUV under consideration as well as on the viscosity of the particle's liquid environment. Therefore, the results evidence that the reduction of the free volume accessible to colloidal motion pushes the diffusion far from a standard Brownian pathway as a result of the change in the hydrodynamic boundary conditions driving the particle motion.

Automated summary

This study aims to investigate the diffusion of biological macromolecules in the cytoplasm, where there is a strict limitation on the accessible volume. By studying the thermal motion of spherical colloidal beads in giant unilamellar vesicles (GUVs), it is found that confinement and environmental viscoelasticity result in anomalous motion pathways for the encapsulated microbeads. This anomalous diffusion is dependent on the ratio between the particle and GUV volume, as well as the viscosity of the particle's liquid environment.