Photos illustrate the difference in the transparency of chicken breast tissue after soaking in tartrazine solutions with an increasing concentration.

Guosong Hong/Stanford University

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The transparent areas take on an orangish color, Ou said, similar to that of the food dye.

The dye used in the solution is commonly known as FD&C Yellow No. 5, certified for use by the US Food and Drug Administration. The synthetic dye is frequently used in orange- or yellow-colored snack chips, candy coating, ice cream and baked goods. However, a 2021 study by the California Office of Environmental Health Hazard Assessment linked the coloring with behavioral difficulties and decreased attention among children. A state bill, if signed into law, would ban the use of the food coloring in food served in public schools in California.

Ou said it was important that the dye is biocompatible — safe for living organisms. “In addition, it’s very inexpensive and efficient; we don’t need very much of it to work,” he said.

Possible biomedical applications for humans

The researchers have not tested the process on humans, and it’s not clear what dosage of dye or delivery method would be necessary. Human skin is about 10 times thicker than that of a mouse, according to the researchers.

“Looking forward, this technology could make veins more visible, easing … the procedure of drawing blood or administering fluids via a needle — especially for elderly patients with veins that are difficult to locate,” said senior author Guosong Hong, a Stanford assistant professor of materials science, via email.

“Moreover, this innovation could assist in the early detection of skin cancer, improve light penetration for deep tissue treatments like photodynamic and photothermal therapies, and make laser-based tattoo removal more straightforward.”

Before and after images show how dye allows researchers to see organs of a mouse by making its skin temporarily transparent.

Stanford University

Christopher Rowlands, a senior lecturer in the department of bioengineering at Imperial College London, said he was “kicking himself” for not coming up with the same insight as the Stanford-led team, which is based on the widely studied and long-standing physics principle called Kramers-Kronig relations: When a material absorbs a lot of light at one color, it will bend light more at other colors.