Scientists have made a rather odd discovery: a food dye commonly used in snack foods can temporarily make mice’s skin transparent. Known as FD&C Yellow 5 or tartrazine, the dye allows researchers to peer inside live mice without cutting them open.
This non-invasive technology could potentially improve human healthcare.
“We found that an aqueous solution of tartrazine, a common food coloring approved by the U.S. Food and Drug Administration, has the ability to reversibly transparentize the skin, muscle, and connective tissue of live rodents,” the researchers report in their study published in Science.org. “Using an absorbing dye molecule, we were able to transform the normally opaque abdomen of live mice into a transparent medium.”
The transparent skin allows scientists to see internal organs and blood vessels without the need for sophisticated medical imaging equipment, and they have already used the chemical to monitor the activity of neurons in the gut in real time and to map intestinal spasms and stretching in mice.
The transparency effect occurs due to a scientific principle called the Lorentz oscillator model, which describes how light interacts with molecules. By absorbing blue light, the dye changes the refractive index of water (how light bends as it passes through it) to make it closer to the refractive index of fats and proteins in tissue.
This reduces light scattering and allows red light to pass more easily through the tissue, thus functionally increasing transparency.
“When the refractive indices of different components in tissue are matched, light scattering is reduced and the tissue appears more homogeneous and transparent,” the study explains.
The researchers first tested the dye on artificial skin, then on chicken breasts, before moving on to live mice, whose scalps were made transparent to expose the blood vessels in their brains, their abdomens to view digestion, and limbs so transparent that individual muscle fibers could be seen.
The team’s experiments go beyond simply clarifying tissue; for example, they used the technique to create time-varying maps of a mouse’s abdomen, showing diverse motility patterns in the digestive system.
Current experiments focus on rodents, but scientists are exploring potential applications in humans.
“Making veins more visible could improve the blood sampling and intravenous therapy process, especially for patients whose veins are difficult to find,” the researchers suggest. Although there are challenges due to the thickness of the human epidermis, the potential is clear.
The dye also has the potential to significantly enhance existing light therapies: photodynamic therapy for cancer could reach deeper tissues, laser tattoo removal could become more efficient, and tartrazine is already FDA-approved for use in food, potentially streamlining future medical uses.
However, as things stand, this process isn’t something you can try at home.
“It could have fatal consequences for the animals and cannot be reversed,” Zhihao Ou, one of the researchers involved in the study, told German news outlet Die Zeit.
“Further toxicity studies are needed before it can be used in humans,” added Ali Erturkum, a neuroscientist at the Helmholtz Centre for Tissue Regeneration in Munich.
But you don’t need a PhD to know that.
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