One-pot synthesis of magnetite-loaded dual-mesoporous silica spheres for T₂-weighted magnetic resonance imaging and drug delivery

The combination of mesoporous silica nanoparticles and superparamagnetic nanocrystals to fabricate multifunctional platforms presents great potentials for simultaneous imaging and drug delivery. In this work, we have successfully developed a simple one-step approach to synthesize magnetite-loaded dual-mesoporous silica spheres consisting of large pores in the core and small pores in the shell (Fe₃O₄@DMSSs) by embedding oil-soluble Fe₃O₄ into the large pores of DMSSs, which were prepared by employing polystyrene-b-poly(acrylic acid) (PS-b-PAA) and cetyl trimethyl ammonium bromide (CTAB) as duallates. The loading amounts of magnetite can be easily adjusted by varying the initial concentrations of Fe₃O₄ nanoparticles in the oil phase. The in vitro test indicates that Fe₃O₄@DMSSs possesses excellent T₂-weighted magnetic resonance (MR) imaging performance with a maximum T₂ relaxivity (r₂) of 421.5 mM_Fe^-1 S^-1. Furthermore, a high doxorubicin (DOX) loading capacity (65 wt%) was achieved and the obtained DOX-loaded Fe₃O₄@DMSSs (DOX/Fe₃O₄@DMSSs) exhibits pH-sensitive behaviour with accelerated release of DOX in acidic environment. Confocal laser scanning microscopy observation shows that DOX/Fe₃O₄@DMSSs was able to locate in the cytoplasm of MCF-7 cells and release DOX into the nucleus to kill cancer cells. Therefore, it is anticipated that Fe₃O₄@DMSSs can be promising candidates as both T₂-weighted MR contrast agents and drug delivery carriers in further biomedical applications.