New Invisible QR Codes Could Thwart Counterfeiters
It's the invisible ink of childhood, all grown up and with a serious purpose.
Researchers have developed a high-tech ink, which they used to print QR (quick response) codes that are invisible in daylight and indoor light. Once placed under a laser, however, the codes light up, like fluorescent green-and-blue versions of the codes sometimes found on ads and signs. These invisible QR codes could someday provide a difficult-to-counterfeit verification mark for currency and more, the code's creators say.
"Printing currency is but one application where this technology could be used," Jon Kellar, a South Dakota School of Mines & Technology engineer who led the development of the glowing code, told InnovationNewsDaily in an email. "It could be used with other legal documents, or protection against counterfeiting of any solid object."
To make the codes, Kellar and his colleagues developed special inks from nanosize particles of rare earth metals and other chemicals. When hit with near-infrared laser light, the chemicals give off higher-energy wavelengths of light, creating a bright color that people can see. Kellar and his teammates made two colors of inks, blue and green. Once made visible by infrared light, the codes are readable by any smartphone equipped with a QR-reading app.
The infrared laser is key. Most fluorescent dyes are read using a higher-energy laser. The techniques for making and reading this infrared-activated fluorescent ink are newer and less known, so they're more difficult to reproduce, Kellar said.
He and a team of materials scientists and chemists in South Dakota developed another security feature for their codes. They found they could use a high-tech printer, called an aerosol jet printer, to print small letters inside the QR codes that don't affect smartphones' ability to read them. They were able to print letters so small they require a microscope to see, as well as letters visible to the naked eye.
The inks could be used to print anything, including bar codes, Kellar said. He and his colleagues decided to print QR codes because they are able to hold 100 times more information than bar codes. The researchers thought they would work well for security, although they are not typically used for security applications now.
The inks work on paper, glass and a plastic film called Kapton, which is used in spacesuits and electronics, Kellar and his colleagues reported in their paper published today (Sept. 12) in the journal Nanotechonology. They also reported their QR codes, when printed onto paper, are still readable after being folded 50 times.
The inks and codes are on their way to real products, Kellar said, although he declined to provide details. "We are currently working with a private sector company to commercialize the technology," he said.