Ion Density Deviations in Semipermeable Ionic Microcapsules

TL;DR

This paper uses nonlinear Poisson-Boltzmann theory to analyze how the permeability of ionic microcapsule shells affects ion distribution and pH deviations inside the capsules, with implications for biosensor design.

Contribution

It introduces a self-consistent theoretical model to study the impact of shell permeability on ion densities and pH deviations in ionic microcapsules.

Findings

Semipermeable capsules induce larger pH deviations than permeable ones.

Increasing capsule charge amplifies the effect of permeability on pH deviations.

The model predicts practical design considerations for biosensor microcapsules.

Abstract

By implementing the nonlinear Poisson-Boltzmann theory in a cell model, we theoretically investigate the influence of polyelectrolye gel permeability on ion densities and pH deviations inside the cavities of ionic microcapsules. Our calculations show that variations in permeability of a charged capsule shell cause a redistribution of ion densities within the capsule, which ultimately affects the pH deviation and Donnan potential induced by the electric field of the shell. We find that semipermeable capsules can induce larger pH deviations inside their cavities that can permeable capsules. Furthermore, with increasing capsule charge, the influence of permeability on pH deviations progressively increases. Our theory, while providing a self-consistent method for modeling the influence of permeability on fundamental properties of ionic microgels, makes predictions of practical significance for the design of microcapsules loaded with fluorescent dyes, which can serve as biosensors for diagnostic purposes.