Controlled Nanostructuring of Multiphase Core-Shell Iron Oxide Nanoparticles

Iron oxide nanoparticles have attracted wide attention due to applications in biomedical sciences like MRI contrast agents, drug delivery, etc. In this work iron oxide ( Fe₃O₄) nanoparticles (NPs) with very narrow size distribution are obtained by using sol-gel method. FeCl₃·6H₂O, ethanol and NaOH are used as precursor, solvent and gelation agent, respectively. Controlled addition of oleic acid helps in the reduction of uncoated particle/crystallite size down to 10 nm and in achieving superparamagnetic behavior of iron oxide NPs. Coating of magnetic NPs is quite important to make them biocompatible and to prevent the aggregation and degradation of metal oxide. Silica, being nontoxic, biocompatible and containing hydroxyl groups attached to its surface, is used for coating purposes. Silica provides hydrophilic properties and thus helps in the attachment of specific drugs and biomolecules. For comparative purposes NPs are also coated by carbon which provides a barrier to oxidation of NPs. XRD studies show the formation of crystalline core shell nanoparticles with decrease in peak intensities as compared to uncoated nanoparticles due to the shielding effect of an amorphous silica shell. Wall thickness of the shell is varied by changing the concentration of ammonia and water to ethanol ratio in silica coated nanoparticles whereas concentration of glucose solution in carbon coated NPs. Coated NPs from 20-50 nm are observed by scanning electron microscopy by changing the concentration of coating solution. Saturation magnetization decreases as the particle size increases due to increased thickness of silica shell. Core-shell nanoparticles show high thermal stability as compared to uncoated nanoparticles.