UV‑responsive tattoo ink tested on silicon hand could guide radiotherapy

A UV‑activated tattoo ink that disappears under bright light was successfully demonstrated on a silicon hand by nanoscientist Carson Bruns, showing promise for medical marking. Bruns, from the University of Colorado Boulder, tattooed his own leg with the invisible ink, which only shows under ultraviolet light and can be erased with visible light. The ink is made of photo‑chromic dyes packed in tiny transparent acrylic spheres; when a UV photon hits, the dye reshapes and becomes visible, and a visible‑light photon reverses the change. Bruns’ team created three colours – magenta, yellow and blue – and tested them on pig skin and silicone models, publishing the results in Matter & Light. The approach builds on photo‑chromic compounds already used in transition lenses and textiles, but adapting them for permanent skin implantation is new, according to Haihui Joy Jiang of the University of Sydney. Bruns previously launched “Magic Ink”, a UV‑magenta tattoo ink commercialized in 2024 through his start‑up HYPRSKN in Boulder. Jake Violi of UNSW Sydney called the invisible, colour‑changing inks an exciting development for both cosmetic and medical tattooing. Potential medical use includes creating temporary markers that guide radiotherapy beams to precise tumor sites, then fading away after treatment. More safety and efficacy tests are required before the inks can be widely offered to patients.## Context The ink works by reversible chemical bonds that change shape under specific light wavelengths, a principle similar to sunglasses that darken in sunlight. This reversible visibility could let doctors place temporary guides that disappear without surgery, reducing long‑term skin markings.