Superparamagnetic iron oxide nanoparticles (SPION) are commonly prepared by co-precipitation, a convenient and high yield producing method. However, this method produces large particles and wide size distribution. Thus, this study aims to optimize and determine the processing condition during the direct co-precipitation synthesis of citrate stabilized SPION (SPION-C). Processing conditions were optimized to achieve the suitable hydrodynamic size and zeta potential; measured straight after preparation, at weeks 3, 10, and 30. Characterization of optimized SPION and SPION-C was done by Fourier transform infrared spectroscopy (FTIR), fluorescence spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The optimized processing condition (stirring speed of 9000 rpm, stabilizer concentration of 1.006 M, and a 90oC stabilizer adsorption temperature), resulted in suitable SPION-C with a hydrodynamic size of 25.58 ± 7 nm, and zeta potential value of -50.8 ± 3.9. Particles with an almost sphere morphology with below 20 nm size were shown by TEM. The XRD analysis presented magnetite phase with a 2.79 nm core size which indicated the formation of stabilized SPION. The maximum excitation and emission wavelength of SPION after stabilization were proved to be uninterrupted by fluorescence spectroscopy. Further FTIR results supported the successful conjugation of citrate onto SPION. Highly stable and crystalline SPION-C were successfully produced through an optimized processing condition using direct co-precipitation. The obtained SPION-C conveyed desired nanoparticle size with narrow size distribution and stability for 30 weeks of storage at 4oC.
