The T2 relaxivity of the SiO2-coated MNPs made from group C was 130 ± 2 mM−1s−1 (Figure 5b), which was approximately 27% lower than that of the original core particles. Group C was BIBW2992 selected for SiO2 coating in order to get final SiO2-coated SPIO MNPs with a diameter of 50 to 100 nm and with a moderate T2 relaxivity value. The SiO2 coating would facilitate the addition of therapeutic BMS202 mw and targeting functions such as drugs and antibodies

to the MNPs, enabling them to serve as both imaging agents and a therapeutic carrier species. Figure 4 Calculated T 2 relaxation rates and relaxivity and representative MR image for the four groups. Concentration-dependent T2 relaxation rates (1/T2) (a), calculated T2 relaxivity r 2 (b) for the four groups at 4.7 T (200 MHz for protons), and representative MR image (c) for the four groups depending on the Co/Fe concentration. The slopes of the fitted lines provide the T2 relaxivity (r 2) at the concentration of 1 mM for each group; the values are 302 ± 9, 268 ± 8, 179 ± 5, and 66 ± 4 mM−1s−1 for groups

A, B, C, and D, respectively. A representative T2-weighted MR image (TE/TR = 10/10,000 ms, slice thickness = 2 mm, number of scans = 2), obtained by a conventional spin-echo pulse sequence on a 4.7-T MRI system, from the samples with four different Co/Fe concentrations (0.25, 0.5, 0.75, and 1.0 mM) for the groups A to D is shown (c). The signal decrease due to T2 negative contrast is higher with increasing Rabusertib ic50 particle size and increasing Co/Fe concentration, especially for group A, which is in accordance with the result shown in (a). Figure 5 TEM images (a) and T 2 property measurement (b) of the SiO 2 -coated MNPs. The TEM images show that the particles consisted of core CoFe2O4 nanoparticles and a SiO2 coating with

a shell thickness of approximately 25 nm, providing a total particle diameter of 70.8 ± 4.3 nm (note the inset for the particle shape in detail). The measured r 2 was 130 ± 2 mM−1s−1, which was 27% smaller than that of the MNP group C core alone. There have been several reports on Fe3O4-based MNPs with a narrow size distribution made by the coprecipitation method. Lee et al. used a piezoelectric nozzle [20], which, despite effectively controlling the particle Lck size, requires specialized equipment and many steps. Jiang et al. employed a coprecipitation methodology using urea, which provided SPIO MNPs with a narrow size distribution [27]. The average diameter of these MNPs could be adjusted from 8 to 50 nm depending on the decomposition of urea in the ferrite solution; however, they required additional dextran coating in order to make them water soluble. In the present study, the use of centrifugation in combination with the coprecipitation method enabled effective regulation of the size of the MNPs without the requirement for a specialist. A large quantity of each size of particles could be produced, overcoming many of the shortcomings of the coprecipitation method.