Fluorescent polycation-coated magnetic nanohybrids (FPMNs) were synthesized for the marking of human mesenchymal stem cells (hMSCs) and non-invasive tracking by both magnetic resonance (MR) and optical imaging. FPMNs were prepared by a polycation-based nanoemulsion method using magnetic nanocrystals (MNCs) as MR probes and polycationic polyethylenimine (PEI) which not only enhanced the affinity for hMSCs but also increased colloidal stability in the aqueous phase. Polycation-coated magnetic nanohybrids (PMNs) were further conjugated with a fluorescent dye (fluorescein isothiocyanate) to serve as optical imaging agents. FPMNs exhibited excellent colloidal stability and biocompatibility as well as high affinity for hMSCs. MR and optical images of hMSCs treated with FPMNs clearly demonstrated abundant potential as brilliant dual-mode imaging agents.
