Designing multifunctional nanomaterials for minimally-invasive biomedical imaging and therapy is an emerging area that integrates imaging and therapy modalities into single functional platform. In this study, we fabricated a multi-functional theranostic platform comprising of (MnxFe1-x)Fe2O4/SiO2 (MFO/SiO2) nanoparticles and fluorescein isothiocyanate. The high saturation magnetization and magnetic susceptibility of MFO/SiO2 provides high relaxivity and specific absorption rate (SAR), which are favorable for high performance MRI and magnetic hyperthermia. The fluorescence signal from the NIH/3T3 cells labeled with the PEGylated fluorescent MFO/SiO2 nanoparticles suggests these nanoparticles passed the cell membrane. The low cytotoxicity, high colloidal stability and the multiple functions demonstrated by our theranostic platform proved its usefulness for multi-purpose biomedical applications. (C) 2017 Elsevier B.V. All rights reserved.