Abstract: Objective： To prepare and characterize citric acid (CA)-modified super paramagnetic iron oxide nanoparticles (SPIONs) for magnetic targeting, hyperthermia and magnetic resonance imaging (MRI). Methods: CA-modified SPIONs (CA-SPIONs) were prepared by co-precipitation method and then the magnetic responsiveness, morphology, particle size, infrared feature, weight percentage of CA, magnetic property and X-ray diffraction pattern of CA-SPIONs were respectively characterized by magnet, transmission electron microscope, laser particle size analyzer, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry-differential thermal analyzer, vibrating sample magnetometer and X-ray diffractometer (XRD). The heating efficiency of the CA-SPIONs was investigated by a high frequency induction heater. The transverse relaxivity (r2) of the CA-SPIONs was evaluated by a 3.0 T MRI scanner. Results: The CA-SPIONs prepared were dispersed well in water with a dark black color and had good magnetic responsiveness. The CA-SPIONs were spherical in shape and uniform in size with an average size around 12 nm. The hydrodynamic average size of the CA-SPIONs was (72.35±4.47) nm with a polydispersity index of 0.231 ± 0.029. The result of infrared spectrum indicated that CA was successfully modified to the surface of SPIONs. The result of thermogravimetric analysis showed that the weight percentage of CA modified on the CA-SPIONs was 9.0%. The result of magnetic property evaluation demonstrated that the CA-SPIONs exhibited excellent superparamagetism with a saturation magnetism of 63.58 emu/g. The XRD result indicated that the CA-SPIONs were in inverse spinel structure. The crystallite size of the CA-SPIONs was calculated to be 12.4 nm by Debye-Scherrer equation. Under the high frequency alternating electromagnetic field with electric current of 9 A and frequency ranging from 45 to 50 kHz, the CA-SPIONs exhibited excellent heating efficiency and the specific absorption rate (SAR) value was calculated to be 26 W/g. The r2 of the CA-SPIONs was assessed to be 338 (mmol/L)-1·s-1 by a 3.0 T MRI scanner, which suggested the excellent negative contrast enhancement effect of the CA-SPIONs. Conclusion: The CA-SPIONs are expected to be used as a promising agent for magnetic targeting, hyperthermia and MRI detection.

Key words: Citric acid, Superparamagnetic iron oxide, Nanoparticles, Magnetic resonance imaging, Magnetic targeting