Silica nanohybrids integrated with CuInS₂/ZnS quantum dots and magnetite nanocrystals: Multifunctional agents for dual-modality imaging and drug delivery

A strategy is presented for the synthesis of dual-modality and theranostic silica (SiO₂) nanohybrids that exert excellent properties for drug delivery vehicles as well as optical and magnetic resonance imaging. SiO ₂ nanohybrids are composed of CuInS₂/ZnS quantum dots and magnetite nanocrystals, with an outside SiO₂ shell grafted with poly(ethyleneglycol) and amine groups to provide better biocompatibility and allow subsequent bioconjugation, respectively. The synthesized nanohybrids are of ultra-small size (diameter < 30 nm) and highly monodispersed and stable in aqueous suspension. In vitro results showed that the SiO₂ nanohybrids were efficiently taken up by the cells and localized in the intracellular vesicles, emitting strong fluorescence from the cytoplasm and nearby nucleus. It was also demonstrated that SiO₂ nanohybrids could be used as a new class of magnetic resonance imaging probes, demonstrating a high spin-spin (T₂) relaxivity (r₂ = 214 mM^-1 s^-1). The Pt(iv) anticancer drug, c,c,t-[Pt(NH₃) ₂Cl₂(O₂CCH₂CH₂CO ₂H)₂], was used as a model drug to attach to the surface of dual-modality SiO₂ nanohybrids by using n-ethyl-N′-(3- dimethylaminopropyl)carbodiimide and hydroxysuccinimide as the activating agents. The drug readily formed amide linkages with amines on the surface of the SiO₂ nanohybrids, resulting in Pt(iv)-conjugated SiO₂ nanohybrids. The results reveal that the Pt(iv)-conjugated SiO₂ nanohybrids show higher cytotoxicity than the free Pt(iv) anticancer drug, indicating the potential for using the obtained multifunctional SiO₂ nanohybrids simultaneously as highly effective dual-modality imaging probes for cancer diagnosis and chemotherapy.