Several reports are available regarding

the size regulation of MNPs synthesized by coprecipitation, including a temperature-controlled coprecipitation method that requires specialized equipment and a piezoelectric nozzle method [20, 21]. These processes are either highly complex or relatively ineffective owing to the requirement for a high level of control over parameters such as temperature during the synthesis. In addition, the produced particles still have an inadequate size distribution. The piezoelectric nozzle method is more effective for controlling the size; however, this technique requires specialized equipment such as a piezoelectric transducer and a frequency amplifier. To address these issues, a facile method for controlling the MNP core size via the coprecipitation find more process is introduced here. Initially, we synthesized CoFe2O4 nanoparticles using an aqueous solution coprecipitation buy CT99021 method and then separated the particles into four groups depending on their size by employing a variety of centrifugation speeds. The physicochemical properties of the four groups were subsequently evaluated. The size distribution was assessed by transmission electron microscopy (TEM) and dynamic light scattering (DLS), crystallographic confirmation was carried out by X-ray diffraction (XRD), the water proton T2 relaxation rate (R 2) versus Co/Fe concentration was evaluated, and

MR image contrast was measured at 4.7 T. Methods Synthesis of CoFe2O4 nanoparticles The CoFe2O4 MNPs were synthesized by an aqueous solution coprecipitation method reported previously [14]. Initially, the reagents, 0.5 M FeCl3·6H2O (≥98%; Sigma-Aldrich, Tokyo, Japan) and

0.25 Thymidylate synthase M CoCl2·6H2O (99% to 102%; Sigma-Aldrich), were mixed in an aqueous solution, giving a Co/Fe ratio of 1:2. The reaction mixture was stirred vigorously for 6 h in boiling distilled water with 1 M NaOH (96%; Junsei, Tokyo, Japan), and then, the resulting dark brown suspension was centrifuged at 1,771 × g. The precipitate was dissolved in a 2-M HNO3 solution with stirring for 20 min and then centrifuged again at 1,771 × g. The resulting precipitate was dissolved in 0.5 M Fe(NO3)3 (≥98%; Sigma-Aldrich) and stirred vigorously for 30 min at 100°C. After the reaction, centrifugation at 1,771 × g and redispersion in distilled water were performed three times. Finally, the suspension was dissolved in water and stored at room temperature until further use. Size selection of MNPs and synthesis of SiO2-coated MNPs As the synthesized MNPs had a broad size distribution between 5 and 300 nm, they were separated depending on their size by stepwise centrifugation. A high-speed vacuum centrifuge system was used (SUPRA 25K; Hanil Scimed, Gangneung, Korea), with five different speeds of 1,771 × g, 2,767 × g, 11,068 × g, 24,903 × g, and 35,860 × g in order to separate the synthesized particles into four groups.