Imaging biological macromolecules in thick specimens: The role of inelastic scattering in cryoEM

We investigate potential improvements in using electron cryomicroscopy to image thick specimens with high-resolution phase contrast imaging. In particular, using model experiments, electron scattering theory, Monte Carlo and multislice simulations, we determine the potential for improving electron cryomicrographs of proteins within a cell using chromatic aberration (C-c) correction. We show that inelastically scattered electrons lose a quantifiable amount of spatial coherence as they transit the specimen, yet can be used to enhance the signal from thick biological specimens (in the 1000 to 5000 angstrom range) provided they are imaged close to focus with an achromatic lens. This loss of information quantified here, which we call specimen induced decoherence, is a fundamental limit on imaging biological molecules in situ. We further show that with foreseeable advances in transmission electron microscope technology, it should be possible to directly locate and uniquely identify sub-100 kDa proteins without the need for labels, in a vitrified specimen taken from a cell.

Automated summary

This study investigates the potential improvements in using electron cryomicroscopy to image thick specimens with high-resolution phase contrast imaging. The research demonstrates that chromatic aberration correction can enhance the imaging of thick biological samples. The study also suggests that with advancements in transmission electron microscope technology, it may be possible to directly locate and identify sub-100 kDa proteins in vitrified specimens taken from cells without the need for labels.