Visualization of Cellulose Structures with Cesium Labeling and Cryo-STEM

Cellulose, a pivotal component of plant cell walls, is a widely studied biologically derived material with vast potential for numerous applications. However, visualizing the arrangement of individual cellulose molecules within hierarchical structures with electron microscopy has proven challenging due to the material's low contrast and high beam sensitivity. In this study, a novel approach is introduced that combines labeling of cellulose functional groups with high-contrast cesium counter cations (Cs⁺) in conjunction with atomic resolution scanning transmission electron microscopy (STEM) in annular dark-field (ADF) mode at cryogenic temperatures. This technique allows for the identification of individual sulfate groups attached to cellulose chains within cellulose nanocrystal hierarchies at Ångström resolution. Systematic comparison of experimentally obtained interatomic Cs⁺ distances with simulations potentially enables the localization of the labeled functional groups at the macromolecular level. The method has the potential to elucidate the polymer chain arrangements in nanoscale soft materials.