Reviewed by Lexie CornerAug 27 2024
A research team from Nagoya University has developed an innovative method for creating anti-counterfeiting labels for high-value products. Their study, published in the journal ACS Applied Materials & Interfaces, demonstrates that the use of fluorescent dyes to produce fluorescent cholesteric liquid crystals (FCLCs) enhances the security of traditional cholesteric liquid crystals (CLCs).
Using this advanced technology, the team created distinctive labels with security features that are nearly impossible to counterfeit. These labels generate unique visual patterns that are difficult to replicate without specialized tools and knowledge, thereby safeguarding valuable items, sensitive information, and delicate goods.
The researchers combined fluorescent dyes with CLCs to produce these specialized tags, causing the crystals' helical structure to twist either left or right—a phenomenon known as chirality. The specific "light signature" produced by the crystals as they reflect light is determined by this twisting. The precise control over the twisting and the resulting light patterns makes these labels extremely difficult to counterfeit.
Under normal lighting conditions, the FCLCs appear as solid colors with no visible information. However, when viewed through a circular polarizer, hidden features emerge, revealing fine details that serve as the first layer of security. Additionally, the FCLCs can include elements that respond exclusively to UV light, providing an additional layer of verification.
The correct information is revealed only when both decoding tools—left circularly polarized light (CPL) and ultraviolet light—are employed. This dual-layer security significantly enhances the protection offered by existing CLC-based anti-counterfeiting tags.
Yukikazu Takeoka, Professor, Nagoya University
The distinctive, iridescent colors of the FCLCs vary according to the chiral dopant concentration and the polarization of the light source, which makes it more difficult for counterfeiters to copy the labels.
The researchers precisely tailored the material to reverse the direction of circular polarization by varying the concentration of the chiral dopant. This allows the FCLCs to absorb left-handed CPL and reflect right-handed CPL, making attempts at counterfeiting even more difficult.
The invention of fluorescent cholesteric liquid crystal (FCLC) particles that display both circularly polarized structural color and circularly polarized luminescence marks a significant advancement in the field of anti-counterfeiting. This innovative approach holds great potential for protecting valuable items and preventing the counterfeiting of sensitive goods.
Looking ahead, this technology could be enhanced with additional security features, such as passwords that become visible only under UV light or QR codes that can be seen exclusively in polarized light, further strengthening its anti-counterfeiting capabilities.
This dual-verification system would provide two layers of protection: the structural color visible under polarized light and the fluorescent emission visible under UV light.
Jialei He, Research Team Member, Nagoya University
FCLCs have the potential to become a vital component of security protocols across various industries, offering an unparalleled defense against counterfeiting and ensuring the authenticity of high-value products.
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.