Synthesis And Application Of Biomedical Magnetic Nanoparticles

1. Superparamagnetic Fe₃O₄ nanoparticles functionalized with carboxymethyl dextran (CM-dextran) were synthesized by a two-step method. First, Fe₃O₄ magnetic nanoparticles (MNPs) coated with dextran (Mw≈20000) were prepared by co-precipitation. Then, dextran on the surface of Fe₃O₄ nanoparticles reacted with monochloroacetic acid in alkaline condition. The obtained nanoparticles were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM) and thermogravimetry (TG). The influences of temperature and reactant concentration on the amount of–COOH on the surface of nanoparticles were systematically studied. The influences of pH and ionic strength for the stability of CM-dextran coated MNPs were also investigated. The obtained Fe₃O₄ MNPs coated with CM-dextran were stable over the entire range of pH and NaCl concentration and exhibited excellent magnetic resonance imaging (MRI) property for cancer diagnosis.2. Polyethlenimine (PEI) has been proposed as alternative cationic polymers that are suitable for gene delivery. The DNA-MNPs polyplexes comprised of PEI coated magnetic Fe₃O₄ nanoparticles (PEI-MNPs) and plasmid DNA was successfully prepared. CM-dextran coated MNPs was synthesized firstly by a two-step method. Then PEI was conjugated to the carboxyl group on the surface of CMD-MNPs by DCC/NHS coupling. At last, PEI-MNPs condense plasmid DNA through electrostatic interactions to form polyplexes. The PEI-MNPs polyplexes exhibited a typical superparamagnetic behavior and were well stability over the entire range of pH and NaCl concentration. DNA-MNPs polyplexes uptake by the cells was monitored by magnetic resonance imaging. The transfection efficiency and gene expression efficiency transfected with a magnet are much higher than standard transfection. 3. Spherical microparticles, capable of responding to magnetic fields, were prepared by encapsulating dextran-coated Fe₃O₄ nanoparticles into chitosan (CS) poly(acrylic acid) (PAA) microspheres template. The CS-PAA microspheres were obtained by polymerization of acrylic acid (AA) in chitosan solution. The obtained magnetic microspheres were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and thermogravimetry (TG). The results showed that the microspheres were formed with a diameter of 100 nm and demonstrated magnetic behavior in an applied magnetic field. In addition, magnetite particles were well encapsulated and the composite particles have high magnetite content, which was more than 40%.