Single particle tracking of nanoparticle probes in homogenous and heterogenous polymer hydrogels

Hydrogels are hydrophilic polymeric networks found extensively in nature and in industrial applications. Many applications of hydrogels depend on understanding the dynamics and the underlying transport mechanisms of probes at the nanoscale in which there are often spatial heterogeneities on the length scale of the diffusing probe. Single particle tracking is a method to investigate particle dynamics at the nanoscale which retains the spatiotemporal characteristics of the diffusing probe, enabling the analysis of nanoscale heterogeneities. In our work, we use sub-10 nm quantum dots to investigate the effect of hydrogel microstructure, gelation and crosslinking density on nanoparticle dynamics. In particular, we find that pH-mediated interactions dominate probe dynamics in the hydrogel nanocomposites and rods diffuse faster than comparable spheres during the gelation of tetra-poly(ethylene glycol). This work offers important insights for predicting and controlling nanoparticle dynamics in gels, applicable to drug delivery and nanoscale filtration.