Core/shell structured hollow mesoporous nanocapsules: A potential platform for simultaneous cell imaging and anticancer drug delivery

A potential platform for simultaneous anticancer drug delivery and MRI cell imaging has been demonstrated by uniform hollow inorganic core/shell structured multifunctional mesoporous nanocapsules, which are composed of functional inorganic (Fe₃O₄, Au, etc.) nanocrystals as cores, a thin mesoporous silica shell, and a huge cavity in between. The synthetic strategy for the creation of huge cavities between functional core and mesoporous silica shell is based on a structural difference based selective etching method, by which solid silica middle layer of Fe₂O₃@SiO ₂@mSiO₂ (or Au@SiO₂@mSiO₂) composite nanostructures was selectively etched away while the mesoporous silica shell could be kept relatively intact. The excellent biocompatibility of obtained multifunctional nanocapsules (Fe₃O₄@mSiO₂) was demonstrated by very low cytotoxicity against various cell lines, low hemolyticity against human blood red cells and no significant coagulation effect against blood plasma. The cancer cell uptake and intracellular location of the nanocapsules were observed by confocal laser scanning microscopy and bio-TEM. Importantly, the prepared multifunctional inorganic mesoporous nanocapsules show both high loading capacity (20%) and efficiency (up to 100%) for doxorubicin simultaneously because of the formation of the cavity, enhanced surface area/pore volume and the electrostatic interaction between DOX molecules and mesoporous silica surface. Besides, the capability of Fe₃O ₄@mSiO₂ nanocapsules as contrast agents of MRI was demonstrated both in vitro and in vivo, indicating the simultaneous imaging and therapeutic multifunctionalities of the composite nanocapsules. Moreover, the concept of multifunctional inorganic nanocapsules was extended to design and prepare Gd-Si-DTPA grafted Au@mSiO₂ nanocapsules for nanomedical applications, further demonstrating the generality of this strategy for the preparation of various multifunctional mesoporous nanocapsules.