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If you’ve been hankering for an intersection of nanomaterials and old spy movie cliches, today’s your day: a gang of researchers in Illinois reckon they’ve found a way to use nanoparticles to make messages that erase themselves after a certain amount of time.

A team at Northwestern University in Evanston, Illinois, coated gold nanoparticles with a layer of hair-like molecules called 4-(11-mercaptoundecanoxy)azobenzene or MUA. When zapped with ultraviolet light, these filaments change their shape and charge distribution, causing the nanoparticles to congregate together and change colour […]

To put this colour-changing ability to good use, the team dispersed the nanoparticles in a gel and sandwiched it between plastic sheets to produce a thin, red film. When Grzybowski and his colleagues shone UV light at the film, either through a patterned mask or using a UV pen, they found they could print a range of images or write words onto the film in just a few seconds.

The colour change is not permanent, however. In the absence of UV light, the MUA gradually reverts to its original shape, allowing the nanoparticles to disperse and the images to disappear.

Your mission, should you choose to accept it, is to work out how many times more expensive and complicated it would be to use this stuff instead of scribbling a note on some rice paper. Or whether the Etch-a-Sketch people will be tempted to build a 2.0 version.