An
invisible quick response (QR) code has been created by researchers in
South Dakota in an attempt to increase security on printed documents and
reduce the possibility of counterfeiting, a problem which costs
governments and private industries billions of dollars each year.

Publishing
their research today, 12 September, in IOP Publishing’s journal
Nanotechnology, the researchers from the University of
South Dakota and South Dakota School of Mines and Technology believe
the new style of QR code could also be used to authenticate virtually
any solid object.

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.

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.

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.

Under
normal lighting conditions the QR code is invisible but becomes visible
when near infra-red light is passed over it. This process, known as
upconversion, involves the absorption of photons by the nanoparticles at
a certain wavelength and the subsequent emission of photons at a
shorter wavelength.

Once illuminated by the near infra-red light, the QR code can be read by a smartphone in the conventional manner.

QR
codes can hold one hundred times more information than conventional
barcodes and have traditionally been used in advertising and marketing.
For example, simply scanning a QR code on a commercial product with a
smartphone will take the user to a company’s website, giving them more
information about the product they are scanning.

The
nanoparticles that were used to print the QR code are both chemically
and mechanically stable meaning they could withstand the stresses and
strains of being placed on paper. To prove this, the researchers printed
the QR code onto a piece of paper and then randomly folded it fifty
times; the code was still readable.

In
addition to being printed on paper, the QR code has also been printed
on glass and a flexible plastic film, demonstrating its applicability to
a wide variety of solid commercial goods. The fact that the QR code is
invisible is also beneficial as it would not interfere with the physical
appearance of the goods.

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, the printing en masse for
commercial use would take around 10 to 15 minutes.

Lead
author of the study, Jeevan Meruga, said: “The QR code is tough to
counterfeit. 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.

“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.”

Security printing of covert quick response codes using upconverting nanoparticle inks

Source: Institute of Physics