In order to combine the advantages of magnetic resonance imaging (MRI) with near-infrared fluorescence (NIRF) imaging

a dual-modality contrast agent is prepared based on MRI and NIRF

which could be used for labeling and tracking rat bone mesenchymal stem cells (RBMSCs). Superparamagnetic iron oxide (SPIO) nanocrystals are prepared by Fe(acac)3

1

2-hexadecanediol

oleic acid

and oleylamine via thermal decomposition method

which posses monodisperse property and uniformly size. Then the contrast agents are used for magnetic resonance imaging (MRI) and near-infrared fluorescence (NIRF) imaging by wrapping the SPIO nanocrystals and IR-780 dye with stearic acidmodified polyethylenimine (stPEI) self-assembly. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) are used to characterize the size and zeta potential

and MRI and IVIS Spectrum System used to characterize the imaging capability. The result shows that the contrast agents are reasonably nano-sized and positively charged. Moreover

the dual-modality contrast agent has showed effective bio and imaging compatibility for labeling and tracking rat bone mesenchymal stem cells (RBMSCs) both in vitro and in vivo.