Synthesis and characterization of core-shell nanoparticles, and a study of their use as encapsulation agents

A mixed-surfactant system was used for the preparation of templates for the synthesis of core-shell particles. One of the amphiphiles used contained silanol groups that were condensed to fortify the templates. Subsequently, a silica coating was chemically attached, obtaining core-shell particles. It was observed by different techniques that the templates and core-shell particles were spherical and their diameter could be tuned by varying component composition. Atomic force microscopy studies after deposition on a hydrophilic substrate showed that these particles flattened dramatically, due to the formation of a flexible matrix in their interior. Formation of the shell increased their rigidity, preventing flattening to a certain degree. An experimental approach based on the use of hydrophobic fluorescent dyes was designed to study the polarity and rigidity of the templates and particles. By using a set of two different probes we found that the polarity of the interior of the particles decreased while its rigidity increased after coating. We used the fluorescence response of these dyes to study the uptake of hydrophobic compounds by the particles. It was determined that, based on their chemical structures, the sequestered probes were placed in different parts of the particles, sensing different environments. We used this information to study the compartmentalization of the interior of the templates and particles by using probes that could undergo resonance energy transfer if they were placed in close environments. These studies suggested that the sequestered probes could interact with each other producing a dynamic quenching of the donor. Finally, we covalently attached another hydrophobic fluorescent probe to the particles to study the level of interaction with the solvent, observing that the probe preferred to react in the interior pores of the particles to reduce interaction with the polar media.