Along with the possibilities of fluorescing dyes and butterfly-wing-inspired printing techniques, there could soon be a new weapon in the fight against counterfeiting – invisible QR codes. Researchers at the University of South Dakota and South Dakota School of Mines and Technology have developed a process for applying such codes to glass, plastic film, and paper products such as bank notes.

The codes are generated using an AutoCAD (computer-aided design) program, and are physically made up of lanthanide-doped nanoparticles blended with blue and green fluorescence ink. They are applied using an aerosol jet printer, and remain invisible to the naked eye. This means that unlike bar codes, they wouldn’t interfere with the appearance of currency, packaging, or any other surface to which they were applied.

When illuminated with near infra-red laser light, the codes become visible. They can then be “read” by a scanning device such as a smartphone, to verify the authenticity of the item in question. In lab tests, codes were still readable after being printed on paper that was subsequently folded in random directions 50 times.

Because the production process is quite complex, the researchers believe that it would be very difficult for counterfeiters to replicate working, accurate QR codes. Things could be made even more difficult for those counterfeiters by embedding microscopic characters and symbols (which would require a microscope to read) within the original code, or by varying the nanoparticle-to-ink ratio.

While the entire design-to-verification process currently takes about 90 minutes, project leader Jeevan Meruga is confident that commercial-scale application of the codes could ultimately take as little as 10 to 15 minutes – it isn’t clear how many applications could be done within that amount of time, but presumably enough to make the technology logistically practical.

A paper on the research was published yesterday in the journal Nanotechnology. More information is available in the video below.

Source: IOP