Some 2 to 5 percent of all international trade involves counterfeit（假冒的） 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 MIT researchers who have developed a new alternative.

Led by MIT chemical engineering professor Patrick Doyle and Lincoln Laboratory technical staff member Albert Swiston, the researchers have invented a new type of tiny, smartphone-readable particle that they believe could be deployed to help authenticate（鉴定） currency, electronic parts, and luxury goods, among other products. The particles, which are invisible to the naked eye, contain colored stripes of nanocrystals that glow brightly when lit up with near-infrared light.

These 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 paper's lead authors are MIT postdoc Jiseok Lee and graduate student Paul Bisso. MIT graduate students Rathi Srinivas and Jae Jung Kim also contributed to the research.