Orange food dye can temporarily turn skin transparent
The dye changes the way skin absorbs light, allowing us to peek inside
Pure Yellow #5 food dye is actually orange and gives many foods, including Doritos, their bright color.
Matthew Christiansen/U.S. National Science Foundation
Someday, doctors might be able to see inside patients without using fancy imaging machines or cutting through the skin. A new solution temporarily turns skin transparent.
The secret ingredient is a food dye found in Doritos, Gatorade and many types of candy. When applied to a mouse’s skin, it allows researchers to see what’s happening inside the animal’s body.
Researchers have shared their findings in Science.
Being able to peer through skin so easily could help us “better understand biology and medicine,” says Lydia Kisley. She did not take part in the new work. She does, however, develop new methods of imaging at Case Western Reserve University in Cleveland, Ohio.
Right now, this imaging “can be done in real time and without requiring invasive surgeries,” Kisley says. “I think this will mainly be used in animals and in the lab first.” In the future, she says, it might also find its way into human medicine.
Letting the light shine through
We see objects when light bounces off of them and into our eyes. Something transparent — such as a window — lets light through. That light can now bounce off objects on the other side of the window and back to our eyes. This is why we can see outdoor objects through the glass.
That is, unless it’s foggy. Light travels at a different speed through through air than through the tiny droplets that make up fog. So instead of light traveling from a tree or building to our eyes, it now bounces off fog droplets in all directions. This turns the air a milky white that’s difficult to see through.
For the same reason, skin is typically not transparent.
Skin contains a lot of water. It also contains fats. If light moved through water and fat at the same speed, we would be able to see through skin. But it doesn’t, so the light scatters. As a result, we can see the skin’s surface, but not what’s beneath it.
The key to turning skin transparent is to allow light to move through the tissue as it does through a window. And that’s where the dye comes in.
Dyes absorb certain hues, or wavelengths, of light. The ones they don’t absorb reflect back to our eyes. That’s the color that we see. To find something that could make skin see-through, researchers tested 21 different types of orange and red dyes. Each absorbs blue wavelengths of light. Removing those blue hues could reduce light scattering.
Materials scientist Zihao Ou led this study while at Stanford University in California. (He now works at the University of Texas at Dallas.) Ou “conducted a comprehensive screening of a large number of common absorbing molecules,” says Guosong Hong. He’s a neuroengineer at Stanford who also took part in the work.
Tartrazine (TAR-truh-zeen) worked especially well. This orangey-red dye colors foods brightly. Since it absorbs bluer wavelengths, it helped light pass through water and fat molecules at similar speeds. That turned skin transparent.
Food dye makes skin see-through
The team mixed tartrazine with water, then tested it on a thin slice of chicken. The meat lay on a light table over lines and words. (A light table is a transparent work surface with a light shining up from below.) As the researchers rubbed the solution into the meat, they soon began to see the words below. When they washed the solution off, the chicken became opaque again and the words disappeared.
The researchers then tried the solution on a sedated mouse. After removing the animal’s fur, they rubbed the dye on its head, belly and leg. Each time, they were able to see inside the mouse’s body.
But the solution didn’t stay only on the mouse’s skin. As it seeped into the animal’s muscles and other tissues, it turned them transparent, too. This allowed the team to spy internal organs, such as a tiny pumping heart and inflating lungs. The scientists needed no special equipment to do this — just the liquid dye and a bright light.
“As soon as we rinsed and massaged the skin with water, the effect was reversed within minutes,” Hong said in a Stanford University press release. “It’s a stunning result.”
The technique is not yet ready for use in people. Our skin is far thicker than a mouse’s. So the dye may not work to peer inside us. Plus, it’s not yet known whether the dye is safe enough to use on human skin, Hong says. But if it is, one day this dye might guide lasers for tattoo removal. It even might replace some X-rays or other body scans to let doctors detect skin cancer without having to cut through the skin.
You can see how well the dye works on a piece of meat at home. But pause for a minute before you mix Dorito dust with water. Instead, carefully follow these instructions and safety guidelines (provided by the National Science Foundation).
Dye may be okay to consume in the small amounts applied to foods. But handling pure food coloring is different. Indeed, Hong notes, the pure dye “should not be [eaten or] applied to people or animals.”
Do you have a science question? We can help!
Submit your question here, and we might answer it an upcoming issue of Science News Explores
