Electrostatic Barriers to Nanoparticle Accessibility of a Porous Matrix

Abstract

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 nanoparticle diffusion within periodic porous nanostructures, where electrostatic interactions were mediated via ionic strength. The effects of electrostatic interactions on nanoparticle transport were surprisingly large. For example, an increase in the Debye length of only a few nanometers (in a material with a hole diameter of ∼100 nm) increased the mean cavity escape time 3-fold. A combination of computational and experimental analyses indicated that this hindered cavity escape was due to an electrostatic energy barrier in the region of the hole, which was quantitatively explained using DLVO theory. These findings explicitly demonstrate that the cavity escape process was barrier-limited and dominated by electrostatic effects.

Mechanisms of transport enhancement for self-propelled nanoswimmers in a porous matrix

“…However, the depletion region obtained from experimental observations of passive Brownian particles was significantly more extended, suggesting long-range repulsion from cavity walls (Fig. 3B), consistent with previous findings (35,36,41). In particular, electrostatic repulsion between cavity walls and passive Brownian particles can inhibit the cavity escape process and decrease the effective hole size, leading to a barrier-limited escape process.…”

“…This can be modeled as a reduction in the apparent hole size. Added salt can screen this repulsion, increasing the effective hole size and accelerating cavity escape (36). Therefore, we performed additional experiments using the same passive particles and porous medium with 0.001 M sodium chloride added, and, as expected, the mean sojourn time was reduced from 68.2 to 32.5 s (Fig.…”

“…The key parameter to characterize cavity escape is the sojourn time, also known as the first passage time through a given cavity. To determine these time intervals, we identified the escape from one cavity to another by monitoring the positional fluctuations in all three dimensions using a maximum allowed displacement algorithm (36). Fig.…”

“…A successful cavity escape consists of two processes: 1) the search for an opening on the cavity and 2) the subsequent translocation through the opening. By directly comparing the motion of nanoswimmers and equivalent passive Brownian particles (31)(32)(33)(34)(35)(36)(37)(38)(39),…”

Kinetics of Nanomedicine in Tumor Spheroid as an In Vitro Model System for Efficient Tumor-Targeted Drug Delivery With Insights From Mathematical Models

“…The neutral charge exhibits the most rapid penetration rate in contrast with the positive and negative charges. Having any kind of charge, whether cationic and anionic, manifests slower penetration due to interaction between the charged particle with the cell surface of the spheroid, resulting in deceleration of their diffusion ( Gao et al, 2013 ; Wu et al, 2020 ). The interaction of nanomedicines with the cell component expelled in the extracellular medium, which is already negatively charged, leads to the change in the size of charged nanomedicines remarkably as compared to the neutral drug molecules.…”