Cellular uptake of FITC-labeled Ce$_{0.8}$Gd$_{0.2}$O$_{2-x}$ nanoparticles in 2D and 3D mesenchymal stem cell systems

Cerium-containing nanoparticles have recently been identified as promising nanozymes for advanced biomedical applications. Additional modification of the core or the surface of CeO$_2$ nanoparticles (CeO$_2$ NPs) provides them with new functionalities, making them a unique theranostic agent. In this study, dextran-stabilized CeO$_2$ NPs doped with Gd (Ce$_{0.8}$Gd$_{0.2}$O$_{2-x}$) were synthesized and further functionalized with fluorescein isothiocyanate (FITC). The synthesized nanoparticles have a high degree of biocompatibility at concentrations up to 5 mg/mL and are readily internalized by human mesenchymal stem cells cultured both in monolayers (2D system) and cellular spheroids (3D system). The functionalization of CeO$_2$ NPs with Gd and FITC dye allows for monitoring their accumulation within organs and tissues using both magnetic resonance imaging (MRI) and fluorescence spectroscopy techniques.