This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: How handy would it be if you could make your tattoos invisible for a job interview in the morning, and reveal them again for a party in the evening? This sounds like science fiction, but it may soon be reality.
Researchers at the University of Colorado Boulder have developed invisible tattoo ink that can be revealed with a UV flashlight and stays visible until switched off with white light. They have published their research in the journal Matter & Light. They created different motifs with this ink ranging from a lantern that reveals its light when activated, to multicolored scales like those in the much-loved children's book "The Rainbow Fish." The pigments used in these inks are so-called photochromic dyes (from the Greek "photos," which means "light," and "chroma," which means "color").
In other words, they are compounds that change color when exposed to light. These dyes have been used for years in color-changing sunglasses. Light carries energy, and photochromic compounds are designed in such a way that this energy is enough to cause a chemical change that alters the shape and therefore the properties of the molecule.
In the case of the "invisible" tattoo ink, two or three seconds of bright ultraviolet (UV) light is enough to form a new ring in the dye molecule, which switches a colorless pigment to a colored one. A variety of colors are available depending on the exact structure of the molecule. A blast of bright white light reverses the reaction, breaking the ring and turning the color off again.
For a long time, the challenge with this chemistry was that the colored form of the dye was relatively unstable and quickly reverted to the more stable, colorless form—especially at higher temperatures. Another issue was fatigue: after a certain number of on-off cycles, the dyes degraded and took on a permanent colored hue. Have you ever bought transition lens sunglasses and noticed that they became less effective over time?
This is due to the same deterioration of photochromic compounds in the lenses. But thanks to recent research efforts, remarkably stable dyes have been designed that reliably hold their color for months and can undergo over 10,000 activation and deactivation cycles without degrading. Carson Bruns' team at the University of Colorado Boulder showed that these pigments could be formulated into tattoo inks by encapsulating them in poly(methyl methacrylate) (PMMA), a polymer approved for medical use in bone cement, dentures and intraocular lenses.
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