Co-Assembly of Cellulose Nanocrystals Through Their Click Chemistry Enabled Surface Functionalization with Single-Stranded DNA

Nature provides in abundance and inspires implementation of functional materials and natural polymers. Among these, cellulose can be further broken down into nanocelluloses, particularly cellulose nanocrystals (CNCs), which are promising candidates in various advanced applications due to their spontaneous self-assembly into complex multifunctional architectures. The chiral twisted assembly of CNCs results in high mechanical strength, iridescent coloration, and polarized light reflection properties, making them excellent candidates for advanced materials. However, engineering nanocomposites with tailored mechanical, thermal, and optical properties requires precise control of the assembly process, including the refinement and tuning of surface chemistry and directed assembly.<br/><br/>In this work, we present a synthetic route for functionalizing CNCs with complementary single-stranded DNA (ssDNA) handles to enable pre-programmed chiral complexation. We employed a three-step process that allowed for hybridization-guided self-assembly of the CNCs, where ultimately the native hydroxyl groups on CNCs were substituted with azide groups to facilitate click chemistry. By grafting functionalized oligonucleotides through copper-free click chemistry, we successfully induced the assembly of DNA-modified CNCs into chiral nanostructures through the complexation of the DNA handles on the CNCs’ surface. Here, in addition to successfully grafting ssDNA onto cellulose nanocrystals to control their interparticle-interactions, we also report their assembly behavior and thus, the feasibility of leveraging CNCs as scaffolds for the assembly of DNA-based nanostructures.<br/><br/>The surfaces of the ssDNA-modified CNCs were studied in detail using high-resolution atomic force microscopy, revealing a moderately grafted with oligonucleotides surface. Additionally, we observed the initial complexation behavior of DNA handles during evaporation-driven formation of CNC films, demonstrating the potential for mediating chiral interactions between the DNA-modified nanocrystals and their assembly into chiral bundles as evidenced by the circular dichroism.<br/><br/>This study demonstrates the feasibility of using click chemistry for CNC bio-functionalization and illustrates how the complexation of individual nanocrystals affects their interactions and organization, leading to the formation of chiral nanostructures. The result is chiral DNA-decorated nanostructures with varying grafting habits and potential for optically active thin films controllably assembled from chemically grafted CNCs.