High-Resolution AFM Visualization of Nanocellulose Surface Grafting with Small Molecules

Nanocelluloses are attractive for bio-based materials development due to their renewability, intrinsic properties, and ease of functionalization. However, characterization of nanocelluloses functionalized with small molecules at low grafting densities is challenging. Here, the use of high-resolution frequency modulation atomic force microscopy (FM-AFM) to directly visualize the covalent grafting of small molecules is demonstrated for the first time. Using epichlorohydrin as a linker, α-cyclodextrin, β-cyclodextrin, and tris(4-tert-butylphenyl)methanol are attached to the surface of bacterial nanocellulose. The presence of these groups is verified through spectroscopic measurements, and their covalent attachment is confirmed with FM-AFM. Furthermore, the retention of cyclodextrin host-guest activity after surface grafting is also demonstrated. This work represents a novel application of FM-AFM for the characterization of small molecule-grafted nanocelluloses, allowing for future development of advanced functionalization strategies.