Synthesis-Dependent Surface Defects and Morphology of Hematite Nanoparticles and Their Effect on Cytotoxicity in Vitro

In this study we investigated the toxicity of hematite nanoparticles on the Madin-Darby Canine Kidney (MDCK) cell line. Hematite precursors were prepared using precipitation and spray precipitation, which were then... [ view full abstract ]

In this study we investigated the toxicity of hematite nanoparticles on the Madin-Darby Canine Kidney (MDCK) cell line. Hematite precursors were prepared using precipitation and spray precipitation, which were then subsequently annealed to form crystalline iron oxide nanoparticles. The crystalline structure, morphology and magnetic properties of these nanoparticles were investigated using X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, and Physical Properties Measurement System. X-ray Photoelectron and Raman Spectroscopy were also used in order to probe the fine structure and surface characteristics. The biological effect of these nanoparticles was also assessed, using a clonogenic assay for overall cytotoxicity, as well as flow cytometric studies to investigate cellular uptake of the nanoparticles, as well as their effects on the cellular reactive oxygen species (ROS) levels.
While the traditional precipitation method produced roughly spherical hematite particles, the use of spray precipitation resulted in highly porous nanorods. Through XPS and Raman analysis it was found that these nanoparticles feature a small defects of maghemite (γ-Fe2O3) on their surface, in the form of tetrahedrally-coordinated Fe3+. This is due to a a thermodynamically-favoured phase transition on their surface due to being formed from amorphous iron oxide precursors. The concentration of these defects were found to decrease when the precursor was annealed at the higher temperature.
It was found that these defects have an effect on the biological activity, with the spherical nanoparticles showing much lowered toxicity and ROS generation than their rod-shaped counterparts. The particles featuring these maghemite defects, which has been shown to scavenge free radical species, even showed to lower the ROS levels in the cytometric assay relevant to the control. The rod shape of the spray precipitation nanoparticles also had preferential uptake into the MDCK cells compared to the spherical nanoparticles.
This work highlights the need for in-depth understanding of the materials properties of nanomaterials in order to understand the factors governing their toxicity, including effects on their fine structure from synthesis parameters.