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Analytical Chemistry

Invisible Ink Gets More Secure

Materials Science: New graphitic carbon nitride quantum dot ink remains out of sight unless exposed to a chemical decryption reagent

by Sarah Everts
February 1, 2016 | A version of this story appeared in Volume 94, Issue 5

Fluorescent inks that are visible only under ultraviolet light are useful for data security and anticounterfeiting but are limited in their usefulness because anybody with a UV lamp can visualize the text. A team based in China has overcome this constraint in several ways. Xinchen Wang and Liangqia Guo at Fuzhou University and colleagues have made a new invisible ink using graphitic carbon nitride quantum dots (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201510945). The ink is invisible under ambient light and under the light produced by common UV lamps. It can be visualized, however, with a fluorescent microplate reader—a piece of specialty equipment. In addition, the new ink’s fluorescence can be quenched with oxalic acid, which acts as an encryption reagent. This chemical lock on fluorescence can be removed using sodium bicarbonate, a decryption reagent. The team points out that the carbon-based quantum dot ink is more photostable than traditional organic dyes used in invisible ink and less toxic than inks containing so-called lanthanide-doped upconverting nanoparticles.


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