Beetle-inspired ink may thwart counterfeiters

On Nov. 5, it was reported by the American Chemical Society that researchers at China’s Southeast University have developed a powerful new weapon in the war against counterfeiting: a color-changing ink that, unlike previous incarnations, is light-resistant, hard to copy, and inspired by a beetle.

This isn’t the first time color-shifting ink has been used to fight forgery. In 1996, the U.S. government redesigned its currency in a bid to slow counterfeiters. The U.S. Department of Engraving and Printing began placing a numeral on the bottom right-hand corner of all $100, $50, and $20 dollar bills using optically variable ink that could change color from (depending on the print date) green to black or copper to green when tilted - a practice still used today. The ink, purchased from Swiss company SICPA, is very expensive and has proven not nearly as effective as the U.S. had hoped, particularly given improvements in digital technology (the Secret Service seized $88.7 million in counterfeit bills in the 2013-2014 fiscal year, 60 percent of which were made using laser and inkjet printers). What’s more, the ink’s color-changing properties fade after prolonged exposure to light and air, and counterfeiters can imitate it using simple household items such as glitter and a blender.

The new ink, however, poses fewer problems to the authorities. According to the journal ACS Nano, the version developed by Zhongze Gu, Zhuoying Xie, Chunwei Yuan, and colleagues is resistant to bleach and light, and can be applied quickly and cheaply with an inkjet printer to both hard and flexible surfaces. The key component is a set of color-changing materials known as colloidal photonic crystals (CPCs), an ordered array of particles which enables the ink to change to a variety of colors and back again when exposed to ethanol vapors. This innovative approach was inspired by Tmesisternus isabellae, a species of longhorn beetle whose color, the team discovered, changed from gold to red according to humidity levels. Like CPCs when exposed to ethanol, the beetle’s scales refract light differently when exposed to water vapor, causing the shift in color.

The new process is also extremely difficult to duplicate - a point the scientists were quick to emphasize in their study.

"The complicated and reversible multicolor shifts of mesoporous CPC patterns are favorable for immediate recognition by naked eyes but hard to copy," they wrote, also noting that the technology can be used for “multifunctional microchips, sensor arrays, or dynamic displays” in addition to anti-counterfeiting devices.

Of course, while the new ink may play a key role when it comes to spotting a fake, other factors  are also important. “It is the combination of security features that are being used that people need to check [when identifying counterfeit currency],” Kevin Billings, a former secret service agent, told “The new bills also have a magnetic strip, facial watermark, and the magnetic raised intaglio printing. All of these security components should be checked before you can safely determine the bill to be genuine.”

Billings also noted that U.S. currency is still being printed on 100 percent rag bond paper at a thickness that cannot be purchased on the open market.

However, as Billings points out, advances in anti-counterfeit measures are worthless if people don’t look for them - no matter how many colors the inks can change. “I have seen five-dollar bills with a zero added in Sharpie successfully pass as a fifty in fast-paced stores where the cashier is new and hurried,” he said.