Application of low-energy scanning transmission electron microscopy for the study of Pt-nanoparticle uptake in human colon carcinoma cells

Abstract

High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) in a scanning electron microscope facilitates the acquisition of images with high chemical sensitivity and high resolution. HAADF STEM at low electron energies is particularly suited to image nanoparticles (NPs) in thin cell sections which are not subjected to poststaining procedures as demonstrated by comparison with bright-field TEM. High membrane contrast is achieved and distinction of NPs with different chemical composition is possible at first sight. Low-energy HAADF STEM was applied to systematically study the uptake of Pt-NPs with a broad size distribution in HT29 colon carcinoma cells as a function of incubation time and incubation temperature. The cellular dose was quantified, that is, the amount and number density of NPs taken up by the cells, as well as the particle-size distribution. The results show a strong dependence of the amount of incubated NPs on the exposure time which can be understood by considering size-dependent diffusion and gravitational settling of the NPs in the cell culture medium.

Keywords::

• electron microscopy
• low-energy HAADF STEM
• nanoparticles
• cells
• quantification of cellular dose

Acknowledgements

The authors would like to thank Prof. M. Türk (Institute for Technical Thermodynamics and Refrigeration, Karlsruhe Institute of Technology, KIT) for providing Pt-nanoparticles. The authors also appreciate fruitful discussions with Dr. Carsten Weiss and Dr. Silvia Diabaté (Institute of Toxicology and Genetics, Karlsruhe Institute of Technology).