A new multicolored tattoo ink called PhotoTat is designed to remain invisible under ordinary light and appear in blue, magenta, or yellow when exposed to ultraviolet (UV) light. The proof-of-concept material, described in a 2026 paper in Physical Review Letters, could eventually provide concealable body art and hidden medical tattoos used to guide radiation therapy.
Ink that appears under ultraviolet light
Many people have tattoos but may sometimes want to conceal them. PhotoTat could offer a way to make tattoo designs invisible to the human eye until they are illuminated with UV light.
“There is a stigma against body art in science and in many cultures,” co-author Carson Brands said. Brands, a professor at the University of Colorado Boulder, has a green lion tattooed on one arm. “I’m proud to be against it.”
Epidermal electronics attached to the skin through temporary tattoos, often called e-tattoos, have been studied for more than a decade. These nearly invisible devices can use ultrathin polymers containing circuit elements to measure electrical signals, temperature, strain, and other properties without adhesive.
In 2024, researchers developed a polymer-based conductive ink that could be printed onto a person’s scalp to measure brain waves even in the presence of hair. The approach could support mobile electroencephalography monitoring and other applications outside clinical settings. Earlier this year, scientists at Pennsylvania State University developed another conductive ink with a customizable colorful design that can be applied directly to skin and becomes a functional electrode after drying.
How PhotoTat works
Brands and his colleagues created PhotoTat using a color-changing dye injected into tiny spheres of polymethyl methacrylate, or PMMA. The material is used in dermal fillers and other medical applications. Combining primary-color dyes allows the ink to produce full-color images.
The tattoo remains invisible until UV exposure causes it to appear blue, magenta, or yellow. The image fades after a few hours and disappears more quickly under bright LED light.
PhotoTat is still a proof of concept. Brands tested the dye on himself by creating the black outline of a fish’s scales. Under UV light, the scales turned red, orange, and blue, producing a mermaid-like effect.
Potential use in radiation therapy
The ink could also be useful for cancer patients undergoing radiation therapy. Patients sometimes receive small tattoos that help doctors accurately guide radiation treatment. With PhotoTat, those marks could remain hidden during daily life and become visible when needed during treatment.
The research is described in Physical Review Letters, 2026, DOI: 10.1103/gbkc-6nlj.
Source: arstechnica.com