Network heterogeneity and structure in synthetic and biological networks are examined using single particle tracking (SPT) of nanoparticles (NPs).  First, we investigate how network confinement and heterogeneity slows NP diffusion in polyacrylamide gels (PEG).  Here, confinement is imposed by increasing the cross-linking density and adding a poor solvent to increase the confinement ratio (CR), the NP diameter divided by the network size.  In both cases, NP diffusion decreases as the CR increases; however, diffusion is more strongly inhibited in the collapsed gel.  This difference was attributed to the larger dynamic heterogeneity in the collapsed gel.  NP diffusion was also studied in tetra-poly(ethylene glycol) gels, which forms a nearly homogenous mesh.  During gelation, both NP mobility and NP spatial coverage decrease as the polymer concentration in the gel increases. NP diffusion is found to be sub-diffusive in the gels.  Further, the NPs become localized within a confining mesh. The onset of sub-diffusivity is marked by a rapid increase in dynamic heterogeneity during gelation providing insight into the mechanism of network formation that occurs at the nanoscale.  NP diffusion is also investigated in responsive gels, namely N-isopropylacrylamide or NIPAAM, near the volume phase transformation temperature.  Finally, we show how SPT provides insight into the cytoskeletal network organization within the cytoplasm by comparing diffusion in normal, cancerous and actin destabilized cells.  Time permitting, recent advances in iSCAT measurements of single gold particle (20nm) diffusion will be described.   In summary, these studies provide an understanding of the interplay between network heterogeneity and small particle (molecule) dynamics, insight that will enhance our understanding of transport in biological systems.<br/>

Nanoparticle diffusion probes network heterogeniety in gels and cells

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.