Photocytotoxicity and Magnetic Relaxivity Responses of Dual-Porous γ-Fe₂O₃@meso-SiO₂ Microspheres

Novel high magnetization microspheres with porous γ-Fe₂O₃ core and porous SiO₂ shell were synthesized using a templating method, whereas the size of the magnetic core and the thickness of the porous shell can be controlled by tuning the experimental parameters. By way of an example, as-prepared γ-Fe₂O₃@meso-SiO₂ microspheres (170 nm) display excellent water-dispersity and show photonic characteristics under externally applied a magnetic field. The magnetic property of the γ-Fe₂O₃ porous core enables the microspheres to be used as a contrast agent in magnetic resonance imaging with a high r₂ (76.5 s^–1 mM^–1 Fe) relaxivity. The biocompatible composites possess a large BET surface area (222.3 m²/g), demonstrating that they can be used as a bifunctional agent for both MRI and drug carrier. Because of the high substrate loading of the magnetic, dual-porous materials, only a low dosage of the substrate will be acquired for potential practical applications. Hydrophobic zinc­(II) phthalocyanine (ZnPC) photosensitizing molecules have been encapsulated into the dual-porous microspheres to form γ-Fe₂O₃@meso-SiO₂–ZnPC microspheres. Biosafety, cellular uptake in HT29 cells, and in vitro MRI of these nanoparticles have been demonstrated. Photocytotoxicity (λ > 610 nm) of the HT29 cells uptaken with γ-Fe₂O₃@meso-SiO₂–ZnPC microspheres has been demonstrated for 20 min illumination.