Scientists have stumbled upon a somewhat surprising discovery: a common food coloring used in snacks can temporarily turn mouse skin transparent. A dye known as FD&C yellow 5 or tartrazine allows researchers to see inside without cutting.
If the non-invasive technique can be modified, it could improve human health care.
We found that an aqueous solution of tartrazine, a common food coloring approved by the US Food and Drug Administration, had the effect of making skin, muscle, and connective tissue transparent in mice. At Science.org. “By absorbing dye molecules, we can convert the irregular stomach lining of a live mouse into a transparent medium.”
Visible skin allows scientists to view internal organs and blood vessels without the need for advanced medical imaging equipment. They've already used the chemical to watch gut neurons fire in real time and measure the twitching and stretching of the gut in mice.
The transparency effect is caused by a scientific principle called the Lorentz oscillator model that explains how light interacts with molecules. The dye works by absorbing blue light, which changes the water's refractive index—how light bends as it passes through it—closer to the fats and proteins in the tissue.
This reduces the scattering of light, allowing the red light to travel more easily through the tissue, making the function clearer.
“When the refractive indices of different parts of the tissue are matched, light scattering is reduced, and the tissue appears more uniform and transparent,” explains the study.
Image: Science.org
Researchers first tested the dye on fake skin, then chicken breasts, before moving on to mice. He made the skulls of rats visible with blood vessels in their brains, making their stomachs transparent to see the act of digestion.
The research team's experiments go beyond making tissues clear. For example, they used the technique to create time-varying maps of the stomachs of mice that show different patterns of activity in the digestive system.
While the current trials are focused on mice, scientists are exploring possible applications in humans.
“Making arteries more visible may improve blood draw or intravenous treatments, especially in patients with difficult access,” the researchers said. A thick layer of humanity presents a challenge, but the potential is clear.
The dye can also complement existing light-based treatments. Photodynamic treatments for cancer can reach deeper tissues, and laser tattoo removal can be more efficient. Also, tartrazine is already FDA approved for food use, which may pave the way for future medical applications.
However, the process is not to be tried at home.
Zhihao Ou, one of the researchers behind the study, told German news outlet Zeit that “it has fatal consequences for the animal and cannot be reversed.”
“You need more toxicity studies before using it in humans,” added Ali Erturk, a neuroscientist at the Helmholtz Center for Tissue Regeneration in Munich.
