Advanced security printing enabled by biomass-derived multicolor anti-counterfeiting fluorescent carbon dot ink with multimodal applications.

Three kinds of N-doped carbon dots (CDs) were synthesized via the solvothermal method using orange juice, lemon juice, and banana leaves as biomass precursors. These CDs exhibited different fluorescence of blue, green, and red with the fluorescence quantum yield (FLQYs) of 16.2%, 14.5%, and 8.4%, respectively. The structure and composition analysis showed that B-CDs and G-CDs were nitrogen doped by urea with the content of about 4%, improving the fluorescence intensity significantly. Notably, the FL of R-CDs were composed of a blue FL emission and a red FL emission, which were inferred to be related to the CDs and chlorophyll-derived porphyrin. Three corresponding CD-based fluorescent inks were prepared by mixing with the thickening agent of glycerol. The application on handwriting, screen printing, and official seal indicated the multilevel UV/visible light dual-mode encryption potential. Furthermore, flexible sensing films were fabricated by incorporating CDs into polyvinyl alcohol (PVA) matrices. Remarkably, the CD-embedded films exhibited significantly enhanced electrical signal responses during mechanical sensing. This work not only provides a novel strategy for high-value utilization of biomass resources but also opens innovative pathways for developing intelligent anti-counterfeiting materials and flexible electronic devices.