Rotational and translational diffusion in ficoll solutions

Abstract

techniques to measure changes of the translational diffusion times and the rotational diffusion times of two nanoprobes, Alexa488 and FITC-Ficoll, dispersed in aqueous Ficoll solutions at room temperature. Analysis of the data indicated that the lifetimes of the nanoprobes appeared to be unaltered by the Ficoll solutions. In contrast, the FCS functions of each nanoprobe, which demonstrated slowing down of diffusion due to Ficoll, were adequately fitted with the expression of a freely diffusing nanoparticle. Similarly, the FA data indicated that the rotational diffusion of both nanoprobes was slowed down. The changes of the diffusion times and the rotational times of both nanoprobes could not be accounted for, however, by the corresponding changes of the viscosity of the solutions. Instead, we applied the entropic model proposed by de-Gennes and his collaborators, and fitted each set of diffusion data with a stretched exponential [exp(- αc n )] with n being related to the quality of the solvent. We determined n-values close to the value one for both nanoprobes and for both diffusions, suggesting a theta-like behavior of the solutions. However, the 􀁄-values for the translation of both nanoprobes were larger than the corresponding ones derived for their rotation, indicating dissimilar local entropic effects. Together with calculations, the present results confirmed the slowing down of the diffusion processes of the nanoprobes due to crowding and, more significantly, provided through the nanoprobes insight into entangled but flexible polymeric structures of the concentrated solutions.