Preparation of dendrimer-loaded microcapsules by a layer-by-layer deposition of polyelectrolytes

Poly(amidoamine) dendrimer-loaded microcapsules were prepared by a layer-by-layer deposition of poly(allylamine hydrochloride) and poly(vinyl sulfate) on the surface of calcium carbonate (CaCO3) microparticles that contain poly(amidoamine) dendrimer, followed by dissolution of CaCO3 core. A fluorescence spectroscopy revealed that a fluorescent dendrimer labeled with trimethylrhodamine is successfully encapsulated in the microcapsules. The leakage of the dendrimer out of the microcapsule was negligible at pH 4.0, while 7% and 25% of dendrimer were released after 6 h in the media at pH 7.0 and 9.0, respectively. The binding and release properties of the dendrimer-loaded microcapsules were evaluated using two kinds of organic dyes Rose Bengal (RB) and 1-anilinonaphthalene-8-sulfonic acid (ANS). RB was accommodated in the microcapsules and released rapidly into buffer solution at pH 8.0, while the release was suppressed at pH 7.0 probably due to binding of RB to dendrimer in the capsules. A fluorescence emission of ANS was highly enhanced in the presence of dendrimer-loaded microcapsules, suggesting a successful binding of ANS to dendrimer in the microcapsules because the fluorescence intensity was not enhanced in the presence of dendrimer-free microcapsules. The kinetic studies revealed that the rate of uptake of ANS in the dendrimer-loaded microcapsules was determined by the rate of transport of ANS across the capsule wall. On the other hand, the dissociation of ANS from PAMAM is the rate-determining step for the release of ANS from the microcapsules.