Microparticle arrays "have potential as covert markers"

Material scientists in the US have developed a new way to make arrays of microparticles that could be used for anti-counterfeit purposes.

The team from Patrick Doyle's lab at Massachusetts Institute of Technology (MIT) in Cambridge say the large-scale microparticle arrays (LSMAs) have "unmatched encoding capacities and rapid decoding capabilities that make them very attractive for a broad range of applications."

Writing in Nature Materials, the scientists describe a method of making LSMAs in which microparticles are guided to and pushed into microwells. The technique means complex arrangements can be made without the limitations of other approaches which "suffer from trade-offs between scalability, precision, specificity and versatility."

They note that spectrally or graphically coded LSMAs are desirable as information carriers because of their high encoding capacity within a small area. For anti-counterfeiting purposes the arrays can be used as covert tags that can only be read when exposed to a near-infrared (NIR) scanner.

The technique has advantages over other ways to create covert tags such as direct inkjet printing and soft lithography, as it generates high-resolution, multicomponent and multi-coloured patterns that have the capacity "to encode every grain of sand on the Earth."

An image of the pattern was taken with an iPhone under NIR exposure and was successfully decoded into a text form within 10 seconds, they note. The approach "expands the utility of particle-based anti-counterfeiting", according to the researchers.

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