Sputtering-Enabled Intracellular X-Ray Photoelectron Spectroscopy (SEI-XPS): A Versatile Method To Analyze The Biological Fate Of Metal Nanoparticles.

The investigation of the toxicological profile and biomedical potential of nanoparticles (NPs) requires deep understanding of their intracellular fate. Various techniques are usually employed to characterize NPs upon cellular internalization, including high-resolution optical and electron microscopies. Here, we show a versatile method, named sputtering-enabled intracellular XPS (SEI-XPS), proving that it is able to provide valuable information about the behavior of metallic NPs in culture media as well as within cells, directly measuring their internalization, stability/degradation, and oxidation state, without any preparative steps. The technique can also provide nanoscale vertical resolution along with semi-quantitative information about the cellular internalization of the metallic species. The proposed approach is easy-to-use and can become a standard technique in nanotoxicology/nanomedicine and in the rational design of metallic NPs. Two model cases were investigated: silver nanoparticles (AgNPs) and platinum nanoparticles (PtNPs) with same size and coating. We observed that, after 48 hours incubation, intracellular AgNPs were almost completely dissolved, forming nanoclusters as well as Ag-O, Ag-S, and AgCl complexes. On the other hand, PtNPs were resistant to the harsh endo-lysosomal environment, and only some surface oxidation was detected after 48 hours.