Doritos have been a favorite snack around the world for decades. One of the dyes that gives the chips their bright pop just did something unexpected in a lab: it helped make mouse skin temporarily transparent, creating “see-through” mice.
That dye is tartrazine, a vivid yellow-orange additive you’ll also find in some foods, medicines, and cosmetics.
Mix a small amount with water, apply it to the skin, and for a short time, cameras tuned to certain wavelengths can see through the top layers.
For people who study living systems, being able to look inside the body without cutting it open is important.
Light usually scatters in tissue, so images blur before you reach anything useful. A simple, safe topical mixture that sharpens the view – even briefly – can open doors for research.
Tartrazine and invisible skin
Researchers at Stanford University described the method in the journal Science.
The approach uses basic optics to reduce scatter and clarify what cameras pick up from living tissue. The idea hinges on changing how water bends light so that it better matches nearby fats in the skin.
“For those who understand the fundamental physics behind this, it makes sense; but if you aren’t familiar with it, it looks like a magic trick,” said Zihao Ou, the lead author of the study who is now an assistant professor of physics at The University of Texas at Dallas.
Living tissue normally looks cloudy
Skin, fat, and muscle aren’t uniform. They’re built from many tiny parts that bend light by different amounts. When light hits those differences, it scatters in many directions. That’s why images fade fast with depth.
Scientists describe how much a material bends light using a value called the refractive index. Water in tissue has a refractive index around 1.33. Lipids sit higher, roughly in the 1.45 to 1.48 range. That gap creates a lot of scatter.
Close that gap, and the path straightens. Less scatter means sharper images and a deeper reach for the same camera and light source.
How tartrazine changes light waves
Tartrazine absorbs blue and near-ultraviolet light. A principle of optics links absorption at one set of wavelengths to changes in refractive index at other wavelengths.
Add a dye that soaks up blue, and you can nudge water’s refractive index upward in the red and near-infrared – the wavelengths that already go deeper into tissue.
Water begins to act a little more like the fats around it, so the light scatters less and the image gets clearer.
The team first checked this in gels and thin tissue slices. The pattern held: there was less scatter where it mattered. Then they moved to live mice and applied a diluted solution to the skin.
To the naked eye, the area looked darker because the dye absorbs blue light. To a camera set for red or near-infrared, the patch turned more transparent for a short time.
“See-through” tartrazine mice
That window was long enough to watch organs move beneath the abdomen. They could follow the gut’s rhythm as it pushed food along.
On the head, they mapped surface blood vessels without shaving to the skull or placing a surgical window.
In a hind limb, they resolved the banded patterns inside muscle fibers – details that usually hide behind layers of scatter. They didn’t cut the skin or implant anything.
Once researchers washed off the dye, the mice lost their translucency, and the dye was excreted in urine, according to the research team.
“It’s important that the dye is biocompatible – it’s safe for living organisms,” Ou said. “In addition, it’s very inexpensive and efficient; we don’t need very much of it to work.”
Neat trick, but why does it matter?
Most methods that clear tissue for imaging work on dead samples. They often dehydrate the tissue, replace fats, or fix it chemically. Those steps can create beautiful static pictures, but they destroy the live dynamics.
This dye-based method leaves tissue alive and flexible. It quiets the optical mismatch just long enough to capture the action. That makes a difference for everyday lab work.
Researchers can track surface blood flow, watch organ motion without surgery, study how nerves in the gut coordinate with muscle contractions, and test new imaging tools with fewer invasive procedures.
Students can learn from live systems while avoiding harsher interventions.
“Optical equipment, like the microscope, is not directly used to study live humans or animals because light can’t go through living tissue,” Ou said.
“But now that we can make tissue transparent, it will allow us to look at more detailed dynamics. It will completely revolutionize existing optical research in biology.”
Tartrazine and future human health
Because the physics ties absorption to refractive index, this strategy isn’t limited to tartrazine. The principle points to a family of agents tuned to the exact wavelengths a microscope uses.
Researchers plan to explore other substances that could outperform tartrazine. The goal is the same: reduce scatter, sharpen images, and do it with materials that are safe, affordable, and easy to apply.
A small change in a fundamental property of water – how it bends light at certain wavelengths – turned cloudy tissue into a temporary window. The method showed live, moving structures in mice.
The immediate win for this study is to provide better, kinder live-animal imaging for biology.
The longer-term promise is a new class of simple add-ons that could help future optical devices “see” a bit deeper at the body’s surface – if safety and performance hold up.
The full study was published in the journal Science.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–