The increasing use of engineered nanoparticles (NPs) in industrial and medical applications has increased the potential for intended and unintended human exposure.  However, the impact of such exposure on living cells and ultimately on human health is still unclear. Cerium oxide (ceria) NPs, in particular, have been shown to induce diverse biological effects, ranging from toxic to beneficial. These disparate effects have been linked to distinct oxidation states of the NPs, but direct measurements of oxidation states in the cellular environment are still missing. Here we used scanning transmission x-ray microscopy (STXM) to measure the oxidation states of ceria NPs in intact hydrated cells, correlated with super resolution fluorescence structured illumination microscopy (SIM) to localize the NPs within distinct organelles. We focused on alveolar epithelial cells, which represent a vulnerable target for airborne NP exposures.  Using STXM, elemental maps and line scan spectra were obtained with 50 nm resolution, along with singular value decomposition from reference spectra, to determine the oxidation state of individual sub-micrometer aggregates of ceria NPs outside and inside the cells. By analyzing hundreds of aggregates, an increase in the fraction of aggregates containing a higher level of Ce3+ was found inside the cells, compared with aggregates outside the cells.  We further used fluorescent antibodies specific to lysosomes and acquired SIM images, which are currently aligned with STXM images to identify the oxidation state of NPs inside the lysosomes. This analysis will determine whether the shift to a higher Ce3+ content occurs early or late in the internalization pathway.  Together with toxicity assessments showing no increase in membrane damage or cell death, our observations indicate that an increase in Ce3+ content takes place in a fraction of ceria NPs as they enter the cellular environment with no adverse effects in these cells.

Shifts in oxidation states of cerium oxide nanoparticles detected inside living cells by correlated X-ray and super resolution fluorescence microscopy

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.