Forged products are a cause for concern across all sectors. They are especially nefarious in the pharmaceutical industry where counterfeit products, due to sub-standard quality, may pose severe health risk to consumers. Each year, multi-million dollar losses are incurred by companies in the global pharmaceutical industry due to presence of counterfeit products in their supply chain. No wonder that the search for solutions is intensifying. Two groups of researchers from China and Spain now made important contributions to the arsenal of anti-counterfeit measures.

The researchers from China’s Fuzhou University developed a high-tech version of invisible ink that can only be seen with a fluorescence microplate reader. Special bonus: The writing can also be encrypted as an additional security measure by modulating its fluorescence with different reagents. The new ink is based on water-soluble quantum dots, consisting of graphitic carbon nitride, a semiconducting material that has low toxicity and is available at relatively low cost. Quantum dots have special optoelectronic characteristics that can be controlled by modifying the size of the dots. The information written with this ink is invisible in ambient or UV light.

To read the information, a special microplate reader is required. The information can be encrypted or decrypted with oxalic acid and sodium bicarbonate as encryption reagent and decryption reagent. The researchers published their findings in the journal Angewandte Chemie (Zhiping Song et al.; “Invisible Security Ink Based on Water-Soluble Graphitic Carbon Nitride Quantum Dots”; Angewandte Chemie; 19 January 2016).

Meanwhile, researchers from Spain tackled the same challenge with a slightly different approach. The group from the University of Zaragoza and CIBER-BBN in Madrid demonstrated that transparent ink containing gold, silver and magnetic nanoparticles could be screen-printed onto different types of paper. The nanoparticles are small enough to disappear into the paper’s pores, making them invisible to humans.

Still, nanoparticles can be detected by the way they refract light and by their magnetic properties. The combination of optical and magnetic signatures is extremely difficult to replicate because they require highly precise fabrication methods and an understanding of the correlation between the characteristics, which makes the inks good candidates for use in anti-counterfeiting measures.

The researchers said that it would be interesting to produce personalized inks with unique signatures for different manufacturers. The ink could be used on paper, plastic and textiles. The scientists published their findings in a recent issue of the journal Nanotechnology.