South Dakota researchers have discovered a way to create
invisible quick response codes, which may be a big help to
discourage counterfeiting. Yes, it’s now possible to create QR
codes that cannot be seen by the naked eye. How? These invisible
QR codes are made from nanoparticles of green and blue
fluorescent ink that can only be seen under near-infrared laser
light. These nanoparticles absorb photons at a non-visible
wavelength then emit them in a visible wavelength. This process
is called upconversion. And only when you have held the QR code
under laser light and it becomes visible can you scan it in the
traditional manner, using your smartphone. This new technique
was developed by researchers from the South Dakota School of
Mines and Technology and the University of South Dakota
specifically as a means of authentication. Because these
invisible codes are complex and because they can have additional
security features — like a specific concentration of
nanoparticles or a different intensity for the upconvert