Cellulose nanocrystal chiral photonic micro-flakes for multilevel anti-counterfeiting and identification

Counterfeiting and forgery have caused enormous economic loss and many safety concerns, and many approaches have been employed for anti-counterfeiting. However, most of these approaches suffer intrinsic issues such as replicability, environmental sustainability, or the requirement of professional equipment to authenticate. Cellulose nanocrystal (CNC) chiral photonic films prepared by evaporation induced self-assembling display iridescent structural colors, circular dichroism, and unique fingerprint texture in microsize, which are promising for anti-counterfeiting. However, the application of CNC films in anti-counterfeiting are severely limited by their brittleness and nonuniformity. Herein, CNC chiral photonic micro-flakes facilely prepared via ultrasonication of CNC films preserve the optical characteristics of CNC chiral photonic films, and can be mixed with polymer matrices to fabricate flexible films or coatings for practical anti-counterfeiting and identification. The anti-counterfeiting characteristics of CNC chiral photonic micro-flakes can be authenticated by an inspection with naked eyes, using 3D glasses, and further with a polarized optical microscope. Therefore, CNC chiral photonic micro-flakes provide a non-replicable, environmentally friendly, easy-to-authenticate, and practical approach for multilevel anti-counterfeiting and identification.