Functionalized Magnetic Multiwalled Carbon Nanotubes And Its Application In Magnetic Resonance Imaging

Molecular imaging emerged in the early twenty-first century as a new discipline, at the intersection of medical imaging and modern molecular biology technology, so it can lead to a wide scope of application in biomedical field. Various types of molecular imaging probes have been developed for fluorescence imaging, magnetic resonance imaging (MRI), nuclear imaging (PET/SPECT), and ultrasonic molecular imaging. Along with the development of nanotechnology, a great deal of attention has been paid to nanomaterials-based molecular imaging probes.Magnetic resonance imaging (MRI) as one of the important molecular imaging technologies possesses non-invasive nature, real-time monitoring and multidimensinal tomographic capabilities, and it can provide the perfect anatomy detailed image for the soft tissue. MRI has further advanced by the development of contrast agents that enable more specific and clearer images, leading to a wide scope of application of MRI not only for diagnostic radiology but also for therapeutic medicine. Current superparamagnetic iron oxide (SPIO) are prevalent in molecular imaging as MRI contrast agent because of their localized shortening of spin-spin proton transverse relaxation times(T2) and effective transverse relaxation times(T2*), thus permit negative contrast enhancement between normal and tumor tissue. By functionalizing SPIO nanoparticles with targeting vectors (i.e. antibodies, biotin), targeting contrast agents for special MRI imaging could be prepared. However, most of magnetic nanoparticles are spherical with limited targeted site attaching to the receptors expressed on the tumor cell surface, and easily cleared by phagocytes, thus active targeting to specific tissue for effectively MRI imaging become very difficult. Therefore, it is necessary to develop a suitable MRI contrast agents, which provide polyvalent binding to amplify particle affinity for cell surface receptors and have an efficient magnetic labeling efficiencies for tumor cells that can enhance the MR signal of the targeting cells.In recently years, the one-dimensional linear nanomaterials have the outstanding advantages in biomedical application. Relative to spherical shapes, these nanomaterials could provide polyvalent binding sites, exhibit low mononuclear phagocytic system (MPS) uptake, prolonged blood half-life. Carbon nanotubes as typical one-dimensional tubular nanomaterials could provide very high surface area per unit weight for high fluorescening nanoparticles, magnetic nanoparticles and targeting biological molecule loading. These composites are expected to be used as a novel molecular imaging nanoprobes.This paper mainly studies the functionalized magnetic mutiwalled carbon nanotubes composites and their utility in magnetic resonance imaging (MRI).1. Fabrication and characterization of magnetic mutiwalled carbon nanotubes.MWNTs/Fe2O3 composites-magnetic mutiwalled carbon nanotubes (MAGCNTs) were synthesized through thermal decomposition of ferrocene to decorate MWNTs with iron oxide nanoparticles. The resulting products were systematically characterized by transmission electron microscopy ( TEM ),vibrating sample magnetometer(VSM),XRD,XPS,Raman.2. Preparation of functionalized magnetic mutiwalled carbon nanotubes and their biocompatibility.Anionic and cationic polyelectrolytes were used to modify magnetic mutiwalled carbon nanotubes (MAGCNTs) via layer-by-layer assembling to obtain functionalized MAGCNTs, in which there are a large of amine groups on their surfaces. The biological properties of functionalized MAGCNTs were analyzed by MTT and flow cytometry. The polymers modified MAGCNTs exhibited good solubility, stability and biocompatibility.3. Targeted MAGCNTs-based contrast agents and their application in magnetic resonance imaging (MRI)Folic acid (FA) as a targeting biological ligand, was further conjugated to the functionalized MAGCNTs composites via amide reaction to obtain the targeted MRI contrast agents. Systematic studies show the novel targeted contrast agent exhibit enhanced MRI effects on the cell level. Furthermore, dual functional imaging molecular probes with optical imaging and MRI were further prepared by decorating CdTe red Quantum dots onto the functionalized magnetic multiwall carbon nanotubes, in which the dual molecular probe for optical imaging could be investigated by confocal laser microscope.