Escape of a Nanoparticle from Cavities in a Porous Matrix

Translocation from one cavity to another through a narrow constriction (i.e. a “hole”) represents the fundamental elementary process underlying hindered mass transport of nanoparticles and macromolecules within many natural and synthetic porous materials, including intracellular environments. This process is complex, and may be influenced by long-range (e.g. electrostatic) particle-wall interactions, transient adsorption/desorption, surface diffusion, and hydrodynamic effects. Here, we used a three-dimensional (3D) tracking method to explicitly visualize the process of passive Brownian nanoparticle and self-propelled Janus particle diffusion within periodic porous nanostructures. Specifically, we quantified the spatial dependence of particle motion and the residence times of individual particles in the interconnected confined cavities, allowing us to test hypotheses regarding the effects of self-propulsion on mass transport in confined porous environments.