Visualizing cellulose chains with cryo scanning transmission electron microscopy

Cellulose, the most abundant biopolymer on earth, is prevalent in the cell walls of plants,
algae, bacteria, fungi, and even some sea animals. Its versatility makes it a valuable
renewable, biodegradable, and non-toxic material for various applications such as papers,
textiles, packaging, and medical products. Within plant cellulose, the cellulose microfibril
(CMF) forms the basic structural element of supramolecular structures. Acid hydrolysis
liberates ordered periodic crystalline regions, forming cellulose nanocrystals (CNCs) with
dimensions of 100-200 nm in length and a few nanometers in width. Despite its abundance
and technological importance, the detailed structure of cellulose remains elusive, with
various proposed models. Transmission electron microscopy (TEM) under cryogenic
conditions offers insights into biomolecular structures. However, imaging cellulose at atomic
resolution is challenging due to its susceptibility to electron beam damage and low contrast.
Here, we present sulfated cellulose chain visualization using low-dose cryo high-resolution
scanning TEM (STEM). We utilize the high contrast provided by heavy ions in annular darkfield
(ADF) imaging to visualize cellulose chains.