An invisible quick response (QR) code has been created by researchers from the University of South Dakota and South Dakota School of Mines and Technology in an attempt to increase security on printed documents and reduce the possibility of counterfeiting.

The QR code is made of tiny nanoparticles that have been combined with blue and green fluorescence ink, which is invisible until illuminated with laser light. It is generated using computer-aided design (CAD) and printed onto a surface using an aerosol jet printer.