Efficient preparation of fluorescent nanomaterials derived from chitin via a modification-first strategy assisted by click chemistry

Fluorescent chitin nanofibers (FChN), as a new type of promising fluorescent nanomaterials, exhibit the characteristics of low toxicity, biocompatibility, biodegradability, sustainability, and high crystallinity and mechanical modulus. However, there is a tradeoff between fluorescence and nanosizing efficiency in processing and conversion of chitin into FChN, because amino groups in chitin are easily converted into fluorescent groups during the first modification process; therefore, FChN are usually prepared with low efficiency via nanosizing first and then modification. Herein, FChN with excellent fluorescence properties were efficiently prepared via a modification-first strategy assisted by a mild and facile click chemistry of partially deacetylated chitins (DEChs). Enough amino groups (22%–30%) were retained in fluorescent DEChs by precise adjustment of reaction activity of amino–yne/hydroxy–yne click chemistry of DEChs, which was the key for the successful preparation of FChN with high efficiency of almost 98%. The first click modification process was mild and had no negative effect on the morphology of FChN, which was similar to that of unmodified chitin nanofibers. In addition, FChN dispersion showed excellent fluorescence and could be used as fluorescent inks for anti-counterfeit printing; FChN films not only showed high fluorescent stability in water, ethanol, DMF, DMSO and 8 wt% NaOH aqueous solution for 30 days, but also exhibited high stress of 200.12 ± 1.70 MPa, excellent UV-blocking properties and controlled biodegradability. This facile and efficient method provides a more sustainable strategy for preparation of functional chitin nanofibers which has high potential for application to anti-counterfeiting, biosensing and smart packaging materials.