Intrinsic fluorescence from cellulose nanofibers and nanoparticles at cell friendly wavelengths

Nanocellulose has emerged as a promising material for many biomedical applications. Depending on the source of the nanocellulose and the chemical treatment, the resulting optical properties can vary significantly. In particular, autofluorescence can exist in various wavelength ranges. Except for chlorophyll related autofluorescence, all other studies have reported intrinsic fluorescence in the blue to yellow range. However, this range coincides with the autofluorescence range of cells. Here, we report on cell friendly red fluorescence of nanocellulose fibers and nanocellulose fiber-derived nanoparticles. Photostability, spectral features, and lifetimes of fibers and nanoparticles are investigated. Subsequently, those nanostructures were successfully integrated into cells, and photostable bright in vitro emission was recorded and analyzed. Our work paves the way to further optical studies of nanocellulose and its related nanostructures, which may find uses in future biomedical applications.