A dye that contributes to the fact that Doritos preserves its orange color can also give tissues of mice transparency, researchers have found. Applying the dye to the skin of living mice enabled scientists to look at the structures underneath through tissue, including blood vessels and internal organs. The method science described on September 6th 1 To monitor animals that are used in medical research purposes.

“It's a big breakthrough,” says Philipp Keller, biologist at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Virginia.

The technology works by changing how normally opaque body parts interact with light. The liquids, fats and proteins from which fabrics such as skin and muscles consist of different refractive indices (a measurement of how much a material bends the light): aqueous components have low refraction indices, while lipids and proteins have a high. Tissue appear opaque because the contrast between these refraction indices means that the light is scattered. The researchers speculated that adding a dye, the light is strongly absorbed, would narrow the difference between the refractive indices of the components to such tissues to make them transparent.

“If a material absorbs a lot of light in one color, it will bend light in other colors," says study author Guosong Hong, material scientist at Stanford University in California. The team used theoretical physics to predict how certain molecules would change the interaction of mouse fabrics with light. Several candidates appeared, but the team focused on Tartrazin or FD & C Yellow 5, a frequently used dye in many processed foods. "When Tartrazin is solved in water, the water makes it more flexible, similar to fats," says Hong. A fabric that contains liquids and lipids becomes transparent when the dye is added, since the light fraction of the liquids of the lipid corresponds.

transparent skin

The researchers showed the ability of Tartrazin to make fabrics transparent on thin slices of raw chicken breast. Then massaged the dye into different areas of the skin of a living mouse. By applying the dye to the scalp, the team was able to examine tiny zigzag patterns of blood vessels; Applying to the stomach offered a clear view of the intestinal movement of the mouse in digestion and revealed other movements in connection with breathing. The team also used the solution on the leg of the mouse and was able to recognize muscle tissue under the skin.

The technology can only make tissue transparent up to a depth of about 3 millimeters, so it is currently practically only for thicker tissue and larger animals of limited use.

But since Tartrazin is a food dye, it is safe for living mice and the method is reversible - if the dye is rinsed off, the skin simply returns. This offers a great advantage over existing methods for the production of transparent tissue, which are usually not suitable for living animals and often require the use of chemicals to change the refractive index of certain tissue components or to remove them completely.

The fact that the method creates transparency, is reversible and can be used in living animals, "makes it an obvious thing that many people want to use," says Keller. He believes that it could be useful among other things in mouse models who want to understand the nervous system and neurodegenerative diseases.