Functional magnetic porous silica for T ₁– T ₂ dual-modal magnetic resonance imaging and pH-responsive drug delivery of basic drugs

A smart magnetic-targeting drug carrier γ -Fe₂O₃@p-silica comprising a γ -Fe₂O₃ core and porous shell has been prepared and characterized. The particles have a uniform size of about 60 nm, and a porous shell of thickness 3 nm. Abundant hydroxyl groups and a large surface area enabled the γ -Fe₂O₃@p-silica to be readily loaded with a large payload of the basic model drug rhodamine B (RB) (up to 73 mg g⁻¹). Cytotoxicity assays of the γ -Fe₂O₃@p-silica particles indicated that the particles were biocompatible and suitable for carrying drugs. It was found that the RB was released rapidly at pH 5.5 but at pH 7.4 the rate and extent of release was greatly attenuated. The particles therefore demonstrate an excellent pH-triggered drug release. In addition, the γ -Fe₂O₃@p-silica particles could be tracked by magnetic resonance imaging (MRI). A clear dose-dependent contrast enhancement in both T ₁-weighted and T ₂-weighted MR images indicated the potential of the γ -Fe₂O₃@p-silica particles to act as dual-mode T ₁ and T ₂ MRI contrast agents. (paper)