Transmission electron microscopy artifacts in characterization of the nanomaterial-cell interactions
We investigated transmission electron microscopy artifacts obtained using standard sample preparation protocols applied to the investigation of Escherichia coli cells exposed to common nanomaterials, such as TiO2, Ag, ZnO, and MgO. While the common protocols for some nanomaterials result only in known issues of nanomaterial-independent generation of anomalous deposits due to fixation and staining, for others, there are reactions between the nanomaterial and chemicals used for post-fixation or staining. Only in the case of TiO2 do we observe only the known issues of nanomaterial-independent generation of anomalous deposits due to exceptional chemical stability of this material. For the other three nanomaterials, different artifacts are observed. For each of those, we identify causes of the observed problems and suggest alternative sample preparation protocols to avoid artifacts arising from the sample preparation, which is essential for correct interpretation of the obtained images and drawing correct conclusions on cell-nanomaterial interactions. Finally, we propose modified sample preparation and characterization protocols for comprehensive and conclusive investigations of nanomaterial-cell interactions using electron microscopy and for obtaining clear and unambiguous revelation whether the nanomaterials studied penetrate the cells or accumulate at the cell membranes. In only the case of MgO and ZnO, the unambiguous presence of Zn and Mg could be observed inside the cells.
KeywordsTEM SEM Nanoparticles Escherichia coli
Financial support from the Strategic Research Theme, University Development Fund, and Seed Funding of the University of Hong Kong are acknowledged.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This paper does not contain any studies with human participants. Ethics approval by The Committee for the Use of Live Animals in Teaching and Research (CULATR 2781-12), the University of Hong Kong, with a valid Cap.340 license was obtained for animal experiments on fish embryos.
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