Template-assisted synthesis of pH-responsive hollow mesoporous silica nanocarriers: the role of engineered pores and surface characteristics

Hollow silica nanoparticles (HSNPs), characterized by a hollow interior enclosed within a solid mesoporous silica shell, offer several advantages, including low density, high surface area, excellent adsorption capacity, and biocompatibility, making them highly attractive for diverse applications in fields such as food, construction, electronics, imaging, and nanomedicine. To investigate the largely unexplored role of the hollow interior and surface functionality in the design of smart nanocarriers, we propose a facile, green-chemistry-based approach for the synthesis of HSNPs, utilizing polystyrene nanoparticles (64 ± 11 nm in diameter) as sacrificial templates. An ultrathin mesoporous silica shell, 10-12 nm in thickness, is conformally deposited through the controlled hydrolysis of a Si precursor, yielding a nanocarrier system that enables the high adsorption of macromolecules with a pH-sensitive desorption profile. Comprehensive analytical techniques reveal that the method of template removal significantly influences both the interior and exterior pore structures. Notably, calcination produces HSNPs with a higher specific surface area ( > 195 m² g⁻¹), a larger average pore diameter ( ~ 20 nm), and an ink-bottle-like mesoporous structure. It is shown that these structural differences, combined with tailored surface functionalities, critically modulate the triggering response of the nanocarrier. To demonstrate functionality, doxorubicin hydrochloride (DOX) was employed as a model drug. A pH-responsive desorption behavior, releasing the biomacromolecule four times faster at pH=4.5 than at pH=7.4, is presented. This finding underscores the impact of surface chemistry and pore architecture on the adsorption and desorption kinetics of macromolecules. The results of this study pave the way for the rational design of stimuli-responsive ceramic nanocarriers with enhanced adsorption efficiency and precise, controlled desorption capabilities.