Smartphone-readable particles could crack down on counterfeiting.
A new type of tiny, smartphone-readable particle that could be deployed to help authenticate currency, electronic parts, and luxury goods, among other products, has been created.
A team of MIT researchers, led by chemical engineering professor Patrick Doyle and Lincoln Laboratory technical staff member Albert Swiston, developed the particles, which are invisible to the naked eye, contain coloured stripes of nanocrystals that glow brightly when lit up with near-infrared light.
Some 2 to 5% of all international trade involves counterfeit goods, according to a 2013 United Nations report. These illicit products – which include electronics, automotive and aircraft parts, pharmaceuticals, and food – can pose safety risks and cost governments and private companies hundreds of billions of dollars annually.
Many strategies have been developed to try to label legitimate products and prevent illegal trade – but these tags are often too easy to fake, are unreliable, or cost too much to implement, according to the researchers who believe their new alternative is the answer.
The new particles can easily be manufactured and integrated into a variety of materials, and can withstand extreme temperatures, sun exposure, and heavy wear, says Doyle, the senior author of a paper describing the particles in the April 13 issue of Nature Materials. They could also be equipped with sensors that can "record" their environments — noting, for example, if a refrigerated vaccine has ever been exposed to temperatures too high or low.
The new particles are about 200 microns long and include several stripes of different coloured nanocrystals, known as ‘rare earth upconverting nanocrystals’. These crystals are doped with elements such as ytterbium, gadolinium, erbium, and thulium, which emit visible colours when exposed to near-infrared light. By altering the ratios of these elements, the researchers can tune the crystals to emit any colour in the visible spectrum.
To manufacture the particles, the researchers used stop-flow lithography, a technique developed previously by Doyle. This approach allows shapes to be imprinted onto parallel flowing streams of liquid monomers — chemical building blocks that can form longer chains called polymers. Wherever pulses of ultraviolet light strike the streams, a reaction is set off that forms a solid polymeric particle.
In this case, each polymer stream contains nanocrystals that emit different colours, allowing the researchers to form striped particles. So far, the researchers have created nanocrystals in nine different colours, but it should be possible to create many more, Doyle said.
Using this procedure, the researchers can generate vast quantities of unique tags. With particles that contain six stripes, there are one million different possible colour combinations. This capacity can be exponentially enhanced by tagging products with more than one particle. For example, if the researchers created a set of 1,000 unique particles and then tagged products with any 10 of those particles, there would be 1030 possible combinations — far more than enough to tag every grain of sand on Earth.