Invisible Mice Do Exist – Here’s How Dye Used in Doritos Made it Happen

Key Takeaways on Invisible Mice

• Invisible mice do exist from recent research that used a type of dye from the chip Doritos to create a transparency effect that lasted about 10 to 20 minutes.
• Research on transparent mice can help us learn more about physiological processes in internal organs and the brain in humans.
• Other researchers have even used the technique in invisible mice to turn a human eye transparent.

There is dye in Doritos, and other similar products, that can be used to turn the skin of mice temporarily invisible, revealing inner organs as a reddish tint.

“Over the course of about five to 10 minutes, the skin became visibly transparent,” says Guosong Hong, a materials scientist and neuroengineer at Stanford University.

Hong says that just by eating Doritos and getting the dye all over your hands, humans are unlikely to get any kind of transparency effect. The dye is unlikely to absorb into your skin without hydrogel or another aqueous solution. But the transparent effect Hong and his colleagues achieved in mice is fascinating, and it can also help researchers learn more about physiological processes in internal organs and the brain in humans.

“It provides a mechanism to see,” says Mark Brongersma, an optics and photonics engineer at Stanford University.

Creating Transparency for Deep Tissue Imaging

Techniques like magnetic resonance imaging (MRI) or X-ray have long helped researchers see past the outer flesh into the body and into our organs. But these techniques aren’t perfect — especially when trying to track what is going on in the brain. Hong, Brongersma, and their colleagues were interested in improving this quality of deep tissue imaging in the human body in their initial study published in Science.

Hong thought about applying the principles of nanophotonics — specifically the Kramers-Kronig relations, which is a theory of how light interacts with different materials and affects their transparency, among other things. Transparency could be achieved based on the way that light is refracted, reflected, or scattered while moving through one material before hitting the next.

In past research, materials like sugar or glycerol were used to try and make items transparent. But high concentrations are needed, Brongersma says, which could dehydrate and damage the tissue.

Hong, Brongersma, and their team decided to focus on reducing the scattering of light in the flesh. Instead of using clear materials, they counterintuitively decided to introduce materials that matched the refractive index of skin with the organs under the flesh — making it more colorful rather than water-clear.

Read More: Medical CT Scans Help Uncover Dinosaur Bones in 100-Year-Old Crates

Are Invisible Mice Real?

Skin — like most things in our bodies — is mostly made up of water, which has a lower refractive index. The other components in tissue like lipids, which include fats, vitamins, and other organic compounds, have a relatively high refractive index. To make skin invisible, the team wanted to raise the refractive index of the water to match the lipids and other components of tissue.

They just needed a molecule with a strong absorption of light. They turned to tartrazine, a molecule often known as Yellow 5 and used in foods like Cheetos and Doritos, to give them those radioactive red, yellow, and orange hues.

“Because of this intense absorption, it appears red,” Hong says.

The team mixed the tartrazine with hydrogel — a type of water gel — and began to rub it into the skin of chicken they bought from the store as an initial test. With some massage work, they could soon see through a few millimeters of chicken breast, though it was tinted red. And the more tartrazine they added, the more transparent the tissue became, Brongersma says.

They then took their gel to anesthetized mice after removing the hair. It only took five to 10 minutes of massaging before the skin became transparent, Hong says. The transparency effect lasted about 10 to 20 minutes before the body metabolized the dye molecules. Researchers could also just wash it off, making the effect easily reversible and quite safe for the mice.

Other Uses for See-Through Mice

Brongersma says other material with a high refractive index could likely achieve the same effect — it doesn’t have to be tartrazine. Researchers using the Kramers-Kronig relations could identify other molecules.

Dozens of different research groups have already made use of the technique in lab work to improve their ability to see what is happening in the gut, brain, and other organs. One group has even made a human eye transparent.

“It’s very nice to see that people are reproducing our work, and that it’s generally applicable,” Brongersma says.

So far, this can be used to make targeted tissues transparent for better visualization. But while it would be exciting to see all organs turn completely invisible, it wouldn’t really help research, which is more about trying to see the interior of the body rather than not see anything at all.

“We need it to become not completely invisible because we can’t learn anything,” Brongersma says.

Read More: Scientists Create a See-Through Solution that Renders Skin Transparent

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