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. SiO2 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(O2CCH2CH2CO2H)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.