Considerations for imaging thick, low contrast, and beam sensitive samples with liquid cell transmission electron microscopy.

Transmission electron microscopy of whole cells is hindered by the inherently large thickness and low atomic contrast intrinsic of cellular material. Liquid cell transmission electron microscopy allows samples to remain in their native hydrated state and may permit visualizing cellular dynamics in-situ. However, imaging biological cells with this approach remains challenging and identifying an optimal imaging regime using empirical data would help foster new advancements in the field. Recent questions about the role of the electron beam inducing morphological changes or damaging cellular structure and function necessitates further investigation of electron beam-cell interactions, but such comparisons are complicated by variability in imaging techniques used across various studies currently present in literature. The necessity for using low electron fluxes while imaging biological samples requires finding an imaging strategy which produces the strongest contrast and signal to noise ratio for the electron flux used. Here, we experimentally measure and evaluate signal to noise ratios and damage mechanisms between liquid and cryogenic samples of intact cells using multiple electron imaging modalities all on the same instrument and with equivalent beam parameters to standardize the comparison. We also discuss considerations for optimal electron microscopy imaging conditions for future studies on whole cells within liquid environments.