The uniform-sized manganese oxide nanoparticles (the oleic-capped MnO NPs) were synthesized by the thermal decomposition of Mn-oleate complex and were transferred into water with the help of cationic surfactant of cetyltrimethyl ammonium bromide (CTAB), then the poly(vinylpyrrolidone) (PVP) membrane was further coated on to them with the aid of anionic dispersant of poly(styrenesulfonate) (PSS) by layer-by-layer electrostatic assembly to render them water soluble and biocompatible. They were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and MTT assay. In vitro cellular uptake test revealed the MnO@PVP NPs were low cytotoxic, biocompatible and could be used as a T,-positive contrast agent for passive targeting magnetic resonance imaging (MRI). Interestingly, signal enhancement in cerebral spinal fluid (CSF) spaces in vivo experiment suggested that the MnO@PVP NPs can pass through the blood brain barrier (BBB). These results show that MnO@PVP NPs are good candidates as MRI contrast agents with the lack of cytotoxicity and have great potential applications in magnetic nano-device and biomagnetic field.
