Recently, our lab has demonstrated a flexible, simple, safe and scalable method of synthesizing microcapsules called as nanoparticle-assembled capsules or NACs [1]. These capsules are synthesized by depositing negatively charged nanoparticles around cationic polyamine aggregates crosslinked by multivalent counteranions. As an example, commercial silica nanoparticles (Snowtex-O) have been deposited on polyallylamine aggregates crosslinked by either citrate or phosphate to form silica NACs [2-3].

We have successfully demonstrated the ability to encapsulate various water-soluble materials like cardiogreen [3] and sodium fluorescein [4] in these NACs. Depending on the application, the encapsulated material is either required to be completely entrapped in the capsule (e.g. photothermal therapy with cardiogreen) or be released at a controlled rate (e.g. drug delivery). The current technique to form NACs presents a porous surface that neither completely contains the encapsulated material, nor releases the material at a predesigned rate. In this study, we attempted to control the permeability of silica NACs by depositing silicic acid on the capsule surface. These studies that were performed with sodium fluorescein as the model encapsulated material will be presented here.

[1] R. K. Rana, V. S. Murthy, J. Yu, and M. S. Wong, "Nanoparticle self-assembly of hierarchically ordered microcapsule structures," Adv. Mater. 17, 1145-1150 (2005)

[2] V. S. Murthy, R. K. Rana and M. S. Wong, “Nanoparticle-Assembled Capsule Synthesis: Formation of Colloidal Polyamine-Salt Intermediates,” J. Phys. Chem. B 110, 25619-25627 (2006)

[3] J. Yu, M. A. Yaseen, B. Anvari, and M. S. Wong, "Synthesis of Near-Infrared-Absorbing Nanoparticle-Assembled Capsules," Chem. Mater. 19, 1277-1284 (2007)

[4] E. M. Tavera, S. B. Kadali, H. G. Bagaria and M. S. Wong, “Experimental and Analytical Modeling Studies of Diffusive Release from Multilayered Microcapsules,” in preparation