A Cryo‐to‐Liquid Phase Correlative Light Electron Microscopy Workflow for the Visualization of Biological Processes in Graphene Liquid Cells

Liquid phase electron microscopy (LP‐EM) has emerged as a powerful technique for in situ observation of material formation in liquid. Especially the use of graphene as window material provides new opportunities to image biological processes because of graphene's molecular thickness and electron scavenger capabilities. However, in most cases the process of interest is initiated when the graphene liquid cells (GLCs) are sealed, meaning that the process cannot be imaged at early timepoints. Here, a novel cryogenic/liquid phase correlative light/electron microscopy workflow that addresses the delay time between graphene encapsulation and the start of the imaging, while combining the advantages of fluorescence and electron microscopy is reported. This workflow allows imaging to be initiated at a predetermined space and time by vitrifying and thawing at a selected time point. The workflow is demonstrated first by observing multiple day crystallization processes and subsequently highlight its potential by observing a biological process: the complexation of calciprotein particles. The ability to correlate the dynamic complexation observed in a GLC with cryogenic TEM and dynamic light scattering, confirms the validity of observations and underlines the exciting possibilities for LP‐EM in biology.