Water-based composite ink from modified chitosan and ruby nanoparticles for advanced anticounterfeiting applications

There is a huge demand for sophisticated materials and innovative strategies to create cost-effective and real-life solutions in security printing field to combat the grave threat due to forgery or counterfeiting of documents and products. In this study, nano ruby is dispersed in an eco-friendly, water-based screen-printing formulation containing modified chitosan as both luminescent colourant and resin to achieve superior security features against counterfeiting. Biopolymer chitosan is modified using 4-bromo-3-hydroxy-1,8-naphthalic anhydride through a green imidation reaction to obtain N-(6-bromo-5-hydroxy-1H-benzo[de]isoquinoline-1,3(2H)-dione) chitosan (CSNA) that display yellow fluorescence, good thermal stability, and low cytotoxicity. CSNA is used as a fluorescent resinated dye to formulate CSNA ink, devoid of any hazardous air pollutants or volatile organic compounds. To improve the security feature, ruby nanoparticles are dispersed in the CSNA ink to achieve nanoruby-CSNA (CSNAR) composite ink, which is further screen-printed on paper substrates. The CSNAR ink film exhibited advanced level security features, wherein the forger can detect only a bright yellow fluorescence from the prints under 365 nm UV light. However, the user can validate the originality of the print by viewing red and yellowish-orange emissions under specific excitation wavelengths, which is unique to the CSNAR ink, and therefore difficult for the forger to replicate. The good adhesion, lightfastness and abrasion resistance of the print combined with the multi-level security features open a new avenue for potential applications of CSNAR security inks/films in document/product authentication and packaging/pharmaceutical anti-counterfeiting applications.