Counterfeit protection through the addition of dye

A research group led by Nagoya University has developed an innovative approach to producing anti-counterfeit labels for high-value goods. Their results, published in ACS Applied Materials and InterfacesImprove the safety of currently used cholesteric liquid crystals (CLCs) by adding fluorescent dyes to produce fluorescent CLCs (FCLCs).

Using this unique technology, the Group has created unique labels with virtually uncounterfeit-proof security features. These advanced labels are designed to protect valuable items, important documents and sensitive products by creating distinctive visual patterns that are difficult to reproduce without specialist tools and knowledge.

To create these special markers, scientists mix fluorescent dyes with CLCs, causing the helical structure of the crystals to twist either to the left or to the right – a property called chirality. This twist determines how the crystals reflect light, creating a specific “light signature.” Precise control of this twist and the resulting light patterns makes these markers nearly impossible to counterfeit.

Under normal light, the FCLCs appear as solid colors with no visible information. However, when viewed through a circular polarizer, hidden features emerge, revealing intricate details that serve as a primary security layer. In addition, the FCLCs may contain components that only respond to ultraviolet light, providing a secondary verification method.

Professor Yukikazu Takeoka of Nagoya University explains: “The correct information is only displayed when both decoding tools – left-hand circularly polarized light (CPL) and ultraviolet light – are used. This two-layer security significantly improves the protection provided by existing CLC-based anti-counterfeiting labels.”

The unique iridescent colors of FCLCs change depending on the concentration of the chiral dopant and the polarization of the light source, making manufacturing even more complicated for counterfeiters attempting to copy the labels.

By carefully adjusting the concentration of the chiral dopant, the researchers fine-tuned the material to reverse the direction of circular polarization, allowing the FCLCs to reflect right-handed CPL and absorb left-handed CPL, further complicating counterfeiting attempts.

The development of FCLC particles with both circularly polarized structural color and circularly polarized luminescence represents a significant milestone in the field of anti-counterfeiting. This innovative approach has enormous potential for securing high-quality goods and protecting sensitive products from counterfeiting.

In the future, this technology could be extended to include additional security features, such as QR codes that are only visible under polarized light or passwords that are visible under UV light. Jialei He, a member of the research team, said: “This dual verification system would provide two layers of protection: the structural color visible under polarized light and the fluorescence emission visible under UV light.”

Thanks to these advances, FCLCs could soon become an integral part of security protocols across many industries, providing unprecedented protection against counterfeit products and ensuring the integrity of high-quality products.