• Posted September 6, 2024

Seeing Through: Scientists Use Food Dye to Render Mouse Skin Transparent

It seems like a kind of superpower, but scientists say they've used a common food dye to render the skin of a mouse transparent, revealing the workings of blood vessels and organs underneath.

It's not yet clear if the procedure could work on human skin, which is thicker than that of a mouse. But the prospect is tantalizing, researchers said.

″Looking forward, this technology could make veins more visible for the drawing of blood, make laser-based tattoo removal more straightforward, or assist in the early detection and treatment of cancers,″ said study co-leader Guosong Hong, a Stanford University assistant professor of materials science and engineering.

″For example, certain therapies use lasers to eliminate cancerous and precancerous cells, but are limited to areas near the skin’s surface," he explained in a news release from the U.S. National Science Foundation. "This technique may be able to improve that light penetration.″  

The Foundation helped fund the new study, which was published Sept. 5 in the journal Science.

Dr. Zihao Ou, an assistant professor of physics at the University of Texas (UT) at Dallas, helped lead the research. In a UT news release, he explained that living skin can't normally be seen through because its various components -- fats, cellular fluids, proteins -- scatter light waves.

But when the researchers applied a mix of water and a safe, long-used yellow food dye called tartrazine to mouse skin, that all changed.

“We combined the yellow dye, which is a molecule that absorbs most light, especially blue and ultraviolet light, with skin, which is a scattering medium," he explained. "Individually, these two things block most light from getting through them. But when we put them together, we were able to achieve transparency of the mouse skin.”

The process could have many lay people still scratching their heads, but essentially the water-dye solution "bends" incoming light in a way that matches major components of skin such as fats.

This reduces the "light-scattering" effect and renders skin translucent, as if a fog had dissipated to make structure beneath the skin clearer.

“For those who understand the fundamental physics behind this, it makes sense; but if you aren’t familiar with it, it looks like a magic trick,” said Ou, who conducted the study while a postdoctoral researcher at Stanford before joining the UT Dallas faculty.

The effects on mouse skin were remarkable: When the solution was rubbed on the skin over the rodents' skulls, the movement of blood vessels beneath the skin was observable.

Similarly, applying the solution to abdominal skin revealed underlying organs as well as the function and movement of the animals' digestive tract.

“It takes a few minutes for the transparency to appear,” Ou noted. “It’s similar to the way a facial cream or mask works: The time needed depends on how fast the molecules diffuse into the skin.”

Rubbing the dye on the skin turns it an orange color and it becomes transparent; rubbing the dye off the skin quickly ends the transparency effect.

You've probably eaten foods dyed with tartrazine -- it's common in orange- or yellow-colored snack chips, candies and other foods, the researchers said. Tartrazine is FDA-approved and is also known as FD&C Yellow #5.

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

The scientists have yet to test the method on human skin, which they noted is 10 times thicker than that of a mouse.

That's a real hurdle, and it's not yet clear which method of delivery (for example, rubbed or injected) might work best on people.

Even if the technique doesn't work on human skin, it still has important implications for medical research generally, the research team believes.

“Our research group is mostly academics, so one of the first things we thought of when we saw the results of our experiments was how this might improve biomedical research,” Ou said. “Optical equipment, like the microscope, is not directly used to study live humans or animals because light can’t go through living tissue. But now that we can make tissue transparent, it will allow us to look at more detailed dynamics. It will completely revolutionize existing optical research in biology.”

More information

Find out about how skin works at the National Center for Biotechnology Information.

SOURCES: University of Texas at Dallas, news release, Sept. 5, 2024; U.S. National Science Foundation, news release, Sept. 5, 2024