Noh Joon-seok's team at Pohang University of Science and Technology POSTECH said on the 6th that it developed an eco-friendly smart security label that reveals authenticity through color and a hologram and disappears without a trace when placed in water.
The importance of anti-counterfeiting technology has been growing recently across a range of products, including food, pharmaceuticals, and luxury goods. At the same time, demand is rising for eco-friendly packaging technologies that reduce plastic waste. However, existing security labels have been limited to simple hologram functions or involve considerable production expense, making them difficult to adopt widely in real industrial settings.
A technology drawing attention as a way to overcome these limits is the "metasurface." A metasurface precisely arranges nanoscale structures to freely change the color and direction of light.
The team created a new material by processing hydroxypropyl cellulose (HPC), derived from plant fiber cellulose, and mixing it with titanium dioxide particles averaging 4–6 nm (nanometers, one-billionth of a meter) in size. HPC is an eco-friendly material with high safety, used in pharmaceutical capsules, food additives, and cosmetics. As a result, nanoparticles became densely embedded inside the HPC, allowing light to be refracted more strongly and controlled more precisely.
A metasurface made from this material produced vivid red, green, and blue in the visible range and displayed a hologram image in the ultraviolet range. This made it possible to contain both color information visible to the human eye and security information verifiable only with specific equipment. The team also implemented an optical security method that hides different holograms inside a QR code, enabling authentication only when three holograms are confirmed simultaneously.
Leveraging the property of HPC to absorb moisture in the air, the structure was designed so that prolonged exposure to environments with relative humidity of 80% or higher deforms the internal structure, causing the color and hologram to disappear. Instead of an electron-beam process that engraves structures one by one, the fabrication used a nanoimprint process that replicates a wide area at once, like stamping, enabling stable production even on plastic films.
The team said, "If the technology is commercialized, it could be applied to various fields, including preventing forgery and alteration of high-priced products and luxury goods, monitoring humidity histories in the distribution of food and pharmaceuticals, and eco-friendly smart packaging systems."
The study was published in the international optics journal Advanced Photonics on Jan. 6 (local time).
References
Advanced Photonics (2026), DOI: https://doi.org/10.1117/1.AP.8.1.016007