Tracking stem cells and macrophages with gold and iron oxide nanoparticles – The choice of the best suited particles

Nanoparticle (NP)-based cell imaging offers good potential for future diagnosis tools in medicine. Gold and iron oxide NPs can be used as contrast agents for imaging by computed tomography (CT) and magnetic resonance imaging (MRI), respectively. Thus, also cells which have been labeled with these NPs may be tracked. This may be important for in vivo tracking of administered or transplanted cells. In this work, we optimized the conditions to label stem cells and macrophages with a library of gold and iron oxide NPs of different sizes (5–100 nm core diameter) and shapes. We investigated the amount of NPs which can be delivered to different cells, as well as their related toxic effects, in relation to the physicochemical properties of the NPs. Our study revealed that in general, when cells are exposed to NPs at similar elemental concentration (e.g., Au or Fe), bigger NPs lead to higher internalized elemental amounts as compared to exposure with smaller sized NPs. While the exposure concentrations are limited concerning the onset of toxicity, bigger NPs lead to better labeling than small NPs, resulting in improved contrast for imaging with enhanced biocompatibility.