Cellulose has historically been a valuable resource that has fueled many industries such as paper, textiles and biofuels. Its hierarchical structure endows it with excellent mechanical properties, which make it attractive for engineering new functional composite materials. Developing these materials requires us to understand cellulose’s structure and be able to visualize it with microscopic resolution. However, there are few routes to efficiently and controllably label cellulose with fluorescent dyes. Here, we present two labeling routes that enable the labeling cellulose with a variety of nct fluorophores. In a first approach, we used trichlorotriazine as a modular linker to synthesize two fluorescent derivatives, dichlorotriazinyl aminofluorescein (DTAF, a commercially available dye), and dichlorotriazinyl piperazine-rhodamine B (DTPR). These derivatives could be grafted directly onto bacterial microcrystalline cellulose (BMCC) through a one-step reaction under mildly basic aqueous conditions. In a second labelling strategy, we used click-chemistry to tag cellulose with a variety of spectrally distinct fluorophores. In this scheme, BMCC and cellulose nanocrystals (CNCs) were first functionalized with dichlorotriazinyl aminopropyne (DTAP) to introduce reactive alkyne groups onto the cellulose surface. This allowed us to then label cellulose with dyes bearing azide functionalities (e.g., azido-fluorescein, azido-Cy5). Through this approach, the degree of labelling of CNCs could be tuned from 0.05 to 34 dyes/CNC by changing the concentrations of the DTAP linker and dye used in the grafting reactions. In a first application, this new labeling approach allowed us to use super-resolution fluorescence microscopy to visualize, for the first time, a repeating pattern of nano-dislocations present on individual cellulose microfibrils. This versatile labelling strategy offers a new and simple method to label cellulose with many commercially-available dyes, allowing the nanoscale characterization of cellulose structure or the visualization of the distribution of nanocellulose in composite materials.

New approaches to the fluorescent labeling of cellulose for visualization at the nanoscale

2019 Spring National Meeting

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