A Cryo-to-Liquid Phase Correlative Light Electron Microscopy Workflow for the Visualization of Biological Processes in Graphene Liquid Cells
Luco Rutten, Ben Joosten, Judith Schaart, Marit de Beer, Rona Roverts, Steffen Gräber, Willi Jahnen-Dechent, Anat Akiva, Elena Macías-Sánchez*, Nico Sommerdijk*
Liquid phase electron microscopy (LP-EM) has emerged as a powerful technique for in-situ observation of material formation in liquid. However, monitoring these processes requires the repeated interaction of the electron beam with the aqueous environment leading to the decomposition of water molecules (radiolysis), which affects the formation processes under investigation. Graphene's ultra-conductive properties have made it an efficient way to mitigate this problem, as it acts as an electron scavenger when used as a window material. Using the strategy, the process of interest is initiated when the graphene liquid cells (GLCs) are sealed. This means that the process cannot be imaged at early time points since microscope preparation and initiation of image acquisition at the region of interest are time-consuming.
Here we report a novel cryogenic/liquid phase correlative light/electron microscopy workflow that addresses the most significant limitations of the graphene liquid cells, while combining the advantages of fluorescence and electron microscopy. This workflow allows imaging to be initiated at a predetermined space and time by vitrifying and thawing at a selected time point. We demonstrate the workflow first by observing multiple day crystallization processes and highlight its potential by observing a biological process: the complexation of calciprotein particles. With this observation, we show the exciting possibilities for LP-EM in biology.
Size-dependent amorphous–crystalline phase transitions in ultra-small gold colloids
Vinavadini Ramnarain, Adrien Moncomble, Maxime Moreaud, Ricardo Gatti, Romain Moreau, Guillaume Wang, Christian Ricolleau, Jaysen Nelayah, Nathaly Ortiz Peña, Alexandre Gelabert, Hakim Amara and Damien Alloyeau*
Understanding the atomic-scale mechanisms governing the structural evolution of ultra-small metal nanoparticles (NPs) is critical for controlling their synthesis and properties in catalysis and nanomedicine. Using aberration-corrected high-resolution transmission electron microscopy in graphene liquid cells, we investigated the dynamics of ultra-small gold colloids at the atomic scale during their growth by Ostwald ripening. This slow coarsening process in which atoms flux between NPs can make them grow or shrink allows us to shed new light on the size-dependent amorphous–crystalline phase transition in gold colloids. Indeed, NPs larger than 2.3 nm are crystalline, while NPs smaller than 1.7 nm are always amorphous. Interestingly, the phase transition between these two phases is systematically observed between 1.7 and 2.3 nm, both during the growth and the dissolution of NPs. The reversibility of this transition suggests a size-dependent equilibrium between amorphous and crystalline phases that is confirmed by Monte Carlo simulations performed within a tight-binding framework. Beyond offering quantitative insights into the phase diagrams of ligand-free gold colloids, these in situ observations provide mechanistic insights into the formation of monocrystalline nanostructures that could help rationalize the growth control of metal NPs.