An invisible quick response (QR) code could be used to stop counterfeit goods because the hidden symbol can only be viewed under infra-red laser light.
The QR code is made of tiny nanoparticles that have been combined with blue and green fluorescence ink, which is invisible until illuminated with NIR laser light. The code is generated using computer-aided design (CAD) and printed onto a surface using an aerosol jet printer. The technology was developed by researchers from the University of South Dakota and South Dakota School of Mines and Technology. According to the researchers, the QR code will add an increased level of security over existing counterfeiting methods as the complexity of the production process makes it very difficult to replicate. Once illuminated by near infra-red light, the QR code can be read by a smartphone in the conventional manner.
‘We can also change our parameters to make it even more difficult to counterfeit, such as controlling the intensity of the upconverting light or using inks with a higher weight percentage of nanoparticles,' said lead author of the study, Jeevan Meruga. Upconversion is where the nanoparticles absorb photons at one wavelength and then emit photons at a shorter wavelength. The research has been published in the Institute of Physics’ peer reviewed journal Nanotechnology. ‘We can take the level of security from covert to forensic by simply adding a microscopic message in the QR code, in a different coloured upconverting ink, which then requires a microscope to read the upconverted QR code,’ Meruga added.
The whole procedure took one-and-a-half hours, from the CAD process to the printing and then the scanning. However, the researchers are confident that once the QR file has been created, printing en masse for commercial use would take about 15 minutes.
The combination of the blue and green inks also enabled the researchers to experiment with a variety of characters and symbols in different colours and sizes, varying from microscopic to macroscopic. Embedding these into the QR code further increases the level of security.
