The Synthesis and Characterizations of O-Carboxymethyl-Chitosan Ultra-small Superparamagnetic Iron Oxide Nanoparticles

OBJECTIVE To develop a novel USPIO-NPs system by surface-modifying superparamagnetic iron oxide nanoparticles (USPIO-NPs) with O-carboxymethyl-chitosans (OCMCS) to improve their biocompatibility and ability to evade reticuloendothelial system(RES). METHODS The OCMCS-USPIO-NP was synthesized by two-step methods: at first, the plain SPIO-NPs was synthesize by alkaline co-precipitation, then the surface of the SPIO-NPs were modified by conjugating the OCMCS to USPIO-NPs, orthogonal experimental design of L9(34) was used to optimize the technology of preparing OCMCS-USPIO-NPs. The resulting USPIO nanoparticles were characterized by dynamic light scattering (DLS), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), zeta-potential measurement and vibrating sample magnetometry (VSM) and MRI. The internalization of uncoated SPIO-NPs, dextran-SPIO-NPs and OCMCS-USPIO-NPs was visualized via prussian blue staining to evaluate the ability of the different SPIO-NPs to escape the macrophage capture. RESULTS The orthogonal experimental design demonstrated that the best technology was as follows: carboxymethyl chitosan molecular weight was 10-20 K, the concentration of OCMCS was 3%, ultrasonic time was 45 min, ultrasonic power was 600 W. FTIR and XRD results confirmed that the successful synthesis of OCMCS-SPIO-NPs. VSM results demonstrated both the modified magnetic Fe₃O₄ nanoparticles and the uncoated SPIO-NPs were superparamagnetic. The results of characterization also demonstrated that the modification with OCMCS results in a drop in hydrodynamic size, saturated hysteresis (r) while lead to a increase in zeta potential. The prussian blue staining in vitro results indicated the internalization of OCMCS-USPIO-NPs into macrophage was much lower than that of dextran-SPIO-NPs and further lower than SPIO-NPs. CONCLUSION The synthesized OCMCS-USPIO-NPs system is stable with hydrodynamic size less than 50 nm, strong electrostatic repulsion, strong super-paramagnetic and low macrophage uptake. Thus, OCMCS-USPIO-NPs system can be a desirable alternative for MRI contrast agent.