Scientists just made mice 'see-through' using food dye — and humans are next

A common food dye can turn the skin of living mice transparent, enabling researchers to peer inside the body without surgery.

This is the first time scientists have used the technique to visualize the tissues of living mice under the microscope. They used a food-safe dye, which can likely be found in snacks in your pantry, and several fundamental physics principles to render the mice see-through.

Biological tissue is chock full of stuff, from proteins to fats and liquids, and each substance differs in its ability to bend, or refract, light that hits it. This property is referred to as a material's refractive index.

If light particles hit a boundary between two materials with different refractive indices, those particles are forced to change direction, or scatter. While light can easily pass straight through transparent materials — like a glass of water — opaque materials get in the light's way, sending it bouncing in many directions. That light then bounces to your eyeballs when you look at the material, and thus, the brain interprets that scattered light as coming from an opaque object. That's why you normally can't see through someone's body.

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But now, scientists have discovered a simple trick to change the skin's transparency: They took a concentrated food dye that is great at absorbing light, dissolved it in water and then applied the solution to the skin, which balanced out the refractive indices of substances within that tissue, making it temporarily translucent.

The researchers described this approach in a new study, published Thursday (Sept. 5) in the journal Science. They tested the technique on rodents using a U.S. Food and Drug Administration-certified color additive called tartrazine, also known as FD&C Yellow No. 5. This yellow-orange dye is often added to foods such as desserts and candy, as well as various drinks, drugs and cosmetics.