Theranostic fluorescent silica encapsulated magnetic nanoassemblies for in vitro MRI imaging and hyperthermia

Abstract

This article reports the synthesis of manganese ferrite nano-assemblies (MNAs) encapsulated with fluorescent silica shell and demonstrates their applicability for magnetic hyperthermia, optical and T₂ contrast MRI imaging with HeLa cancer cells. The MNAs were encapsulated by a double layer of silica shell through a two-step sol–gel process. The inner silica shell contains rhodamine-B isothiocyanate (RITC) dye, whereas the outer silica layer is without RITC-dye, helps to prevent photo-bleaching and increase photo-luminance. MNAs@Dye–SiO₂@SiO₂ exhibited a high magnetization of 90.43 emu g⁻¹ with a remarkably high r₂ value of 598 ± 2 mM⁻¹ s⁻¹ (Mn + Fe). The cellular uptake of MNAs@Dye–SiO₂@SiO₂ was observed by the presence of fluorescent red granulated spots in the cytoplasm of HeLa cells, confirming its efficacy for optical imaging. High transverse relaxivities r₂ (darkening effect) were observed in HeLa cells incubated with MNAs@Dye–SiO₂@SiO₂ in comparison to HeLa cells without particles. An 80–85% cell death was achieved on induction of magnetic hyperthermia with HeLa cells at the lowest H_f factor value (3.3 × 10⁹ A m⁻¹ s⁻¹). Our results show MNAs@Dye–SiO₂@SiO₂ as a novel multifunctional theranostic nanoprobe, which can realize its applicability for diagnostic and real time monitoring the efficacy of ongoing cancer therapy.