A tattoo with an on-off switch: colour appears under UV light and fades again
Engineers at the University of Colorado Boulder have developed tattoo inks that are normally invisible. Under UV light they turn blue, magenta or yellow within seconds.
Archive image · Photo: Dave Dugdale / Wikimedia Commons, CC BY-SA 2.0 (cropped and resized)
A team led by Carson Bruns at the University of Colorado Boulder has developed tattoo inks that can be switched on and off with light. The inks, called PhotoTat, combine light-responsive dyes with tiny glass-like spheres of PMMA, a plexiglass-like plastic that is also used in some medical products such as dermal fillers. The study has been published in the journal Matter & Light.
Normally the dyes are invisible. Under ultraviolet light they turn blue, magenta or yellow within seconds and fade again over several hours; bright LED light switches them off faster. Mixing the primary colours makes full-colour designs possible. "PhotoTat is like a switch," says Bruns, who tested the inks on his own leg.
In medicine, such inks could replace the small markings used to align radiation therapy for cancer, which currently remain permanently visible. However, safety in humans has not yet been established, and PhotoTat is not available at tattoo parlours. The team plans to keep developing the inks over the coming years.