All groups can be seen to exhibit the same peaks, which match well with the standard Fe3O4 XRD pattern (JCPDS 75–0030). The mean particle size (D) can be calculated by the check details full-width at half-maximum

(FWHM) and the area/height ratio (β) of the XRD peaks with instrumental correction, using the equation D = Kλ / β × cosθ, where K is the Scherrer constant, λ is the wavelength, β is the FWHM (in radians), and θ is the peak angular position [22, 23]. The XRD information gave crystallite sizes of 14.9, 13.2, 12.1, and 7.3 nm (Figure 3). As MNPs synthesized by coprecipitation may contain some iron oxide crystals, the particle size calculated from the TEM images was larger than that from the XRD data (Figure 3b). Selleckchem Captisol Figure 3 A stack plot of XRD patterns of MNPs and size calculation. The nanoparticles were well crystallized, H 89 clinical trial and the peaks are in accordance with the typical CoFe2O4 XRD spectrum in which the main peaks are (111), (220), (311), (400), (511), and (440) (a). The mean diameters of the crystal particles calibrated from signal width for the four groups from A to D

were 14.9, 13.2, 12.1, and 7.3 nm, respectively (b). The size-dependent MR contrast (T2 relaxivity) of the MNPs was measured on a 4.7-T MRI system. Figure 4a shows the dependence of the T2 relaxation rate (R 2, s−1) on the MNPs of the four groups. The T2 relaxation rate was increased with increased Co/Fe

concentration, and the T2 relaxivities (r 2) for the groups were measured from the slopes of the data. The r 2 values were found to be 302 ± 9, 268 ± 8, 179 ± 5, and 66 ± 4 mM−1s−1 for groups A, B, C, and D, respectively (Figure 4b). These values are comparable to those Rebamipide in the study of Joshi et al. [24], in which the T2 relaxivity of cobalt ferrite nanostructures synthesized by the thermal decomposition method was reported to be 110 to 301 mM−1s−1 depending on the particle size (6 to 15 nm). Figure 4c shows an MRI phantom image with the four groups depending on the Co/Fe concentration measured on the 4.7-T MRI system. The increase in MR T2 negative contrast was shown to depend on both the particle diameter and the Co/Fe concentration, indicating that a well-controlled contrast with each size-selected group of MNPs could be obtained. The particle size dependence of T2 relaxivity was in accordance with other reports [25, 26], in which T2 spin-spin relaxation is affected by mass magnetization depending on the magnetic particle size in the range lower than approximately 1 μm. This demonstrates that each group of MNPs could be used for specific applications depending on the particle diameter. One concern regarding these as-prepared MNPs is that they are not stable to variations in pH. This is a problem that needs to be overcome if they are to be successfully employed in vivo.