STEM mode in the SEM: A practical tool for nanotoxicology

Abstract

The addition of a transmitted electron detector to a scanning electron microscope (SEM) allows the recording of bright and dark field scanning transmission electron microscope (STEM) images and the corresponding in-lens secondary electron images from the same region of a thin sample. These combined imaging techniques have been applied here to the analysis of ultrathin sections of cells exposed in vitro to nanomaterials for toxicology investigation. Electron microscopy in general permits the exact nature of the interaction of nanomaterials and cells to be elucidated, and in addition the use of STEM mode in the SEM enables the easy identification and exclusion of artefacts produced by ultramicrotome sectioning. The imaging and analysis obtained by using the STEM mode in the SEM configuration from three different nanomaterial systems of importance (iron oxide nanoparticles, single-walled carbon nanotubes and cadmium selenide quantum dots) indicate that it is a simple, practical and cost-effective tool for nanotoxicological research.

Keywords::

• Scanning transmission electron microscopy
• field emission scanning electron microscopy
• STEM mode in the SEM
• nanotoxicology
• ultrathin sections

Acknowledgements

The authors wish to thank Dr Alice Warley, Dr Anthony Brain and Mr Ken Brady (Centre for Ultrastructural Imaging, King's College London) for expert sample preparation and Mr Gordon England (KE Developments Ltd) for useful discussion regarding the STEM detector configuration.

Declaration of interest: The authors wish to acknowledge the University of Leeds, Swansea University, MRC (G0700865/82417), The Colt Foundation and EPSRC (EP/E059678/1 and EP/H008578/1) for financial support. Initial results were obtained using the Leeds EPSRC Nanoscience and Nanotechnology Research Equipment Facility (EP/F056311/1). The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.