Recent interest is focused on microcapsules stabilized using colloidal nanoparticles - termed 'colloidosomes - for encapsulation applications in food, drug and cosmetic industries. However, due to electrostatic repulsion between similarly charged particles, shells composed of single-type nanoparticles tend to be monolayer-thick and relatively permeable. We investigated a self-assembly method for controlling the permeability of colloidal shells using aggregates composed of oppositely charged silica nanoparticles. Using a combination of rapid fluorescence based method and theoretical diffusion models, we found that colloidosomes whose shells contained colloidal silica aggregates displayed lower permeability to peroxyl radicals than ones stabilized by single type of silica nanoparticles. Furthermore, the permeability varied as a function of the ratio of oppositely charged silica nanoparticles in the shell. The ability to control the permeability of colloidosomes, while using a simple self-assembly synthesis method, will enable enhanced control over release kinetics and oxidative stability of encapsulants. (C) 2013 Elsevier Ltd. All rights reserved.