Deborah Sandrin wins the best presentation award at the Workshop FCS in Polymer Science, September 24th-25th, 2015 RWTH Aachen.
Title: Quantitative experimental and theoretical investigation of diffusion of macromolecules through gel matrices
Abstract:
The dynamical hindrance of polymers molecules diffusing through a polyacrylamide gel is systematically explored using dextran over a broad range of their molecular weight, applying three complementary methods. While Multiparameter Fluorescence Image Spectroscopy (MFIS) is applied to investigate the local diffusion of single molecules on a microscopic length scale inside the hydrogel, a macroscopic transmission imaging technique (MTI) and nuclear magnetic resonance (PFG-NMR) are used to study the collective motion of particles through the gel matrix. Interestingly, we find quantitative agreement for the long-time diffusion coefficient of the dextran molecules. The measured diffusion coefficients decay markedly with increasing molecular weight and fall on a master curve provided they are scaled with the free diffusion in the absence of the matrix. The trends are also described with Brownian dynamics simulations. We used a realistic model where the gel is described as floppy soft matrix: the model employs two contributions of forces. The steric interactions are represented by a repulsive Lennard-Jones potential and the attractive region assumes the size of the dye´s radius. In particular in MFIS we observe 3 different classes of td: fast, middle and slow component. We found temporarily trapped particles for td > 10 ms inside the matrix. The investigation of the interaction between gel and probe is studied under different salt conditions and clearly shows the dependency of the fraction of immobile molecules with the ionic strength. The temporary trapping was also confirmed by anisotropy measurements and a significant heterogeneity of the gel was shown. MTI method supports the idea of the interaction with Alexa-labeled particles and gel, showing that the fluorescence intensity of the hydrogel was higher than of the surrounding solution at the end of the measurement.