C. Zhang, et al., Nature Communications, 10.1038/s41467-017-01248-2, 2017

This new invisible ink can be switched on and off on demand

The next James Bond might have a hard time decoding top secret documents. Researchers have developed a lead-based invisible ink that, unlike its predecessors, is colorless under ultraviolet (UV) light until a salt is added to make it glow. What’s more, the ink can be switched off on demand using another chemical trigger: Add methanol, and it vanishes within 10 minutes. The researchers have used the ink to print on parchment paper both text and more complex patterns, such as QR codes and butterflies (pictured, as they appear under a UV lamp after adding the salt). After being switched on and off 20 times, the ink didn’t lose its bright color under UV light, and could be kept in open air for 3 months without degrading, the team reports today in Nature Communications. Because lead-based materials can be toxic, the researchers hope to design lead-free alternatives that could make the new ink a go-to tool for security and privacy protection.