Biodegradable dye-doped silica fluorescent coating: multifunctional nanoparticles for cell assays and toxicity reduction

In vivo imaging and therapy represent one of the most promising areas in nanomedicine. Particularly, the identification and localization of nanomaterials within cells and tissues is a key issue to understand their interaction with biological components, namely their cell internalization route, intracellular destination, therapeutic activity and possible cytotoxicity. Here, we show the development of multifunctional nanoparticles (NPs) by providing luminescent functionality to zinc (ZnO) and iron oxide (Fe3O4) NPs, which have already demonstrated cellular toxicity and application in nanotherapy for imaging and cancer treatment, respectively. Specifically, we describe simple synthesis methods based on modified Stöber procedures to incorporate fluorescent molecules on the surface of oxide NPs. These procedures involve successful coating of NPs with a size-controlled shell of amorphous silica (SiO2) incorporating standard chromophores like fluorescein, rhodamine B or rhodamine B isothiocyanate. Our coating procedures allow identification and location of ZnO and Fe3O4 NPs inside the cellular cytoplasm using confocal microscopy imaging. Besides, the SiO2 shell provides a platform for further functionalization that enables the design of targeted therapeutic strategies. Finally, we studied the degradation of the shell in different physiological environments.