Danger Dust

Through a subtle effect, a yellow pigment found in Cheetos snack food enables light to travel straight through tissue

To see what’s going on beneath the skin, doctors depend on an array of expensive imaging techniques—x-rays, ultrasound, magnetic resonance imaging, endoscopy, etc. However, a team of materials scientists has found a simpler way to see into the body—of mice at least. Applying a common pigment renders the skin of the animals temporarily transparent, the researchers report today in Science, revealing the organs beneath. (And just in case you still have your appetite: The pigment is one of those used to give the snack food Cheetos its distinctive orange color.)

Light travels through water at three-quarters its speed in a vacuum, making water’s index of refraction 1.33. Air has a refractive index slightly above one. When light passes through materials with different refractive indices, its path bends. It’s the same principle that allows the lenses in your glasses to focus light onto your retinas.

In tissues, the lipids that make up cell membranes have a refractive index of about 1.4, higher than the surrounding water. So, the cells act like so many randomly oriented lenses that scatter light in all directions.

Existing techniques can render tissues—and even entire mice—transparent by removing the lipids and leaving a watery gel, allowing light to pass through without scattering. But because these techniques destroy cell membranes, they can’t be applied to living animals.