You may have seen those odd-looking black and white stamps on an advertisement or similar document. QR codes, as they’re called, are similar to barcodes in that they contain data about the object they’re stamped on. Now a team from two South Dakota universities have come up with a way to put QR codes on documents that are invisible to the naked eye but visible to a smartphone camera or laser-light reader. The key is in the ink: The nanoparticles in it help it to glow bright blue or green when exposed to near-infrared light.
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What’s the Big Idea?
Invisible QR codes are just one more way to stop counterfeiters from duplicating sensitive documents. In addition to the code data itself, the researchers figured out a way to embed a microscopic image into the stamp as well, making the document that much more difficult to forge. The ink can be used with a desktop printer to allow printing on ordinary documents, and paper’s not its only medium: “[B]ecause the code can be printed on plastic or even glass, manufacturers could use it to authenticate other items.”