Ultrasmall inorganic molecular imaging probes

In this study, nearly monodisperse cobalt ferrite (CoFe2O4) and zinc ferrite (ZnFe2O4) nanoparticles (NPs) without any size-selection process have been fabricated through an alluring method in an oleylamine (OAM)/benzyl ether system. Samples were synthesized by thermal decomposition of metal acetylacetonates in a high-boiling solvent and in the presence of oleylamine as surfactant and reducing agent. XRD analysis confirmed the purity and nanosized of both products and TEM analysis showed the monodispersion of them also. The oleylamine coated nanoparticles exhibited semiconducting nature at lower frequencies i.e. conductivity enhances with temperature. The dc conductivity curves of ZnFe2O4@OAm and CoFe2O4@OAm NPs indicate significant temperature-dependent behavior. The temperature and frequency-dependent variations of dielectric loss (ε″) of MFe2O4@OAm NPs display an almost sharp exponential decrease with frequency which becomes more considerable at higher temperatures and at low at low frequency regime. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values have been determined. Although the Mössbauer spectra for the ZnFe2O4@OAm consists only one paramagnetic central doublet and CoFe2O4@OAm NPs have also one paramagnetic doublet and three magnetic Zeeman sextet.