Core–shell superparamagnetic iron oxide nanoparticle (SPION) clusters: TEM micrograph analysis, particle design and shape analysis

For the first time, particle shape analysis of silica coated iron oxide (maghemite/magnetite) nanoparticle clusters (core–shell nanostructures) is discussed using computational methods. We analyzed three samples of core–shell nanostructures synthesized with different thickness of the silica shell. A new computational method is presented and successfully applied to the segmentation of the core–shell nanoparticles, as one of the main problems in image analysis of the TEM micrographs. We have introduced the “circularity coefficient”, marked with kcirc and defined as the ratio of circularity measure C2(S) of nanoparticles core and circularity measure core–shell nanoparticles in order to answer the question how the shell affects the overall shape of the final core–shell structure, with respect to circularity. More precisely, the “circularity coefficient” determines whether the circularity of the core–shell nanoparticle is higher, lower or equal to the circularity of the core. We have also determined the shell's share in the overall area of the core–shell nanoparticle. The core–shell nanoparticle clusters here investigated exhibit superparamagnetic properties at room temperature, thus emphasizing their potential for use in practical applications such as in biomedical and particle separation. We show that the saturation magnetization strength can be easily adjusted by controlling the thickness of the silica shell.