Liquid STEM

A novel method for electron microscopy of whole eukaryotic cells in liquid with nanometer spatial resolution was recently introduced. A specimen in liquid is placed in an enclosure with electron transparent windows and imaged using a STEM. The STEM, which exhibits a particular sensitivity to materials of high atomic number, is used to image nanoparticles in a layer of liquid. Labels of different sizes and compositions can be distinguished. Liquid STEM will be used to investigate distributions of proteins in cells at the nanoscale, and also to study cellular processes by correlating light microscopy with electron microscopy. Liquid STEM offers the potential to combine the ultra-high resolution of electron microscopy with much of the functionality of light microscopy. The liquid STEM microchips and liquid specimen holder are provided by Protochips Inc. (NC).

State-of-the-art 3D electron microscopy makes use of tilt-series, or the averaging of signals of many identical particles. A new option is provided by 3D STEM in which the electron beam is scanned in three dimensions, similar as the optical sectioning of confocal laser microscopy. This technique has become available with a meaningful vertical resolution due to the enlarged beam opening angle of the aberration corrected STEM. 3D STEM appears of particular interest for structural biology, while it offers fast imaging times, absence of drift problems, the possibility to image large area samples, the option to image thick samples and high sensitivity for specific labels. 3D STEM has been demonstrated to work for conventional thin sections.

The research was funded by NIH project grant R01-GM081801. Dr. David.W. Piston has taken over the role of principal investigator after the transfer of Dr. Niels de Jonge to the INM-Institute in Saarbruecken, Germany.

Monte-carlo calculations of beam-sample interactions are performed in collaboration with Prof. Dominique Drouin of the University of Sherbrooke (Canada) using Casino software.