A team of researchers from Nagoya University has developed a revolutionary method to combat counterfeiting, using fluorescent cholesteric liquid crystals (FCLCs) to create highly secure labels for valuable products. Their research, published in *ACS Applied Materials & Interfaces*, highlights the enhanced security these labels offer compared to traditional cholesteric liquid crystals (CLCs).
The key to these labels lies in the unique combination of fluorescent dyes with CLCs. This fusion creates a helical structure within the crystals, which twists either left or right â a phenomenon known as chirality. This twisting directly influences the way the crystals reflect light, generating a unique "light signature" that's incredibly difficult to replicate without specialized knowledge and equipment.
These FCLC labels appear as solid colours under normal lighting, but reveal hidden features when viewed through a circular polariser. This acts as a first layer of security, unveiling intricate details that serve as a visual verification mechanism. Adding to this complexity, the FCLCs also incorporate elements that respond exclusively to ultraviolet (UV) light, providing an additional layer of authentication.
Professor Yukikazu Takeoka from Nagoya University explains the dual-verification system: "The correct information is revealed only when both decoding tools â left circularly polarised light (CPL) and ultraviolet light â are employed. This dual-layer security significantly enhances the protection offered by existing CLC-based anti-counterfeiting tags."
Further enhancing their security, the researchers have successfully manipulated the material to reverse the direction of circular polarisation by altering the concentration of the chiral dopant. This allows the FCLCs to absorb left-handed CPL and reflect right-handed CPL, further complicating any attempts at counterfeiting.
The researchers' ability to create FCLC particles that exhibit both circularly polarised structural colour and circularly polarised luminescence marks a significant advancement in the fight against counterfeiting. This innovative approach holds great potential for safeguarding valuable items, particularly in industries dealing with high-value goods or sensitive information.
Jialei He, a member of the research team, elaborates on the dual-verification system: "This dual-verification system would provide two layers of protection: the structural colour visible under polarised light and the fluorescent emission visible under UV light."
Looking ahead, the researchers believe that this technology can be further enhanced with additional security features like passwords visible only under UV light or QR codes detectable exclusively through polarised light. These additions would further strengthen the anti-counterfeiting capabilities of FCLCs.
The potential of FCLCs to become a vital component of security protocols across various industries is significant. By offering unparalleled protection against counterfeiting, FCLCs could play a crucial role in ensuring the authenticity of high-value products and combatting the global problem of counterfeit goods.
Journal Reference:
He, J., *et al*. (2024) Circularly Polarized Luminescence Chirality Inversion and Dual Anticounterfeiting Labels Based on Fluorescent Cholesteric Liquid Crystal Particles. *ACS Applied Materials & Interfaces*. doi.org/10.1021/acsami.4c08331.
