An improved methodology for imaging cellulose nanocrystals by transmission electron microscopy

Abstract

Although transmission electron microscopy (TEM) is a method of choice for the analysis of cellulose nanocrystals (CNCs), it is still a challenging technique to use due to the low electron density and aggregation issues associated with this material. This work presents a robust and reproducible method to image CNCs by TEM, without the need for staining. It is demonstrated that low pH and hydrophilic TEM grids favored high dispersion of the sample for optimal imaging. Electron beam and voltage settings are also discussed. Three distinct types of CNCs are analyzed: never-dried, freeze-dried and spray-dried CNCs. Although a few reports accounted for mushroom structures, we demonstrate herein that, regardless of the sample history, this nanomaterial is always rod-shaped. The rods were measured to be 9.7 ± 4.4 nm in width and 216 ± 82 nm in length. By dismissing the use of heavy metal staining, multi-component systems, for instance, palladium nanoparticles onto CNCs, could be imaged by TEM.