Yellow Dye 5 may be the key to invisibility

The same dye that gives Twinkies their yellowish color may be the key to invisibility.

Applying the dye to lab mice made the animals' skin temporarily transparent, allowing Stanford researchers to see the animals' digestive systems, muscle fibers and blood vessels, the Stanford researchers announced. study Released on September 5th Science.

“This is an amazing result,” said Dr. Guosong Hong, an assistant professor of materials science and engineering at Stanford and lead author of the paper. “If the same technology could be applied to humans, it could have a variety of benefits in biology, diagnostics and even cosmetics.”

The research drew on an optical concept first described in the early 20th century to develop a surprising theory: applying a light-absorbing substance could make skin transparent by reducing the random scattering of light when it hits the proteins, fats and water in tissue.

The search for a suitable light-absorbing agent led to the synthetic colorant FD&C Yellow 5 (also known as tartrazine). Accreditation It is approved by the U.S. Food and Drug Administration for use in foods, cosmetics, and drugs.

When live mice were coated with tartrazine (after removing some of their hair with a drugstore depilatory cream), the skin on their abdomens, hind legs, and heads became transparent within five minutes. With the naked eye, the researchers observed the functioning of the mice's intestines, bladders, and livers. They also used a microscope to view the muscle fibers of live mice, and even looked at blood vessels in their brains — all without making any incisions. When the dye was washed off, the transparency quickly faded.

In the future, the concept could be used in clinics and hospitals, Hong said.

“Instead of relying on invasive biopsies, doctors may be able to diagnose deep-seated tumors simply by examining a person's tissue, without the need for invasive surgical removal,” he said. “This technology could potentially make blood draws less painful by making it easier for phlebotomists to find veins under the skin. It could also improve procedures like laser tattoo removal by allowing them to more precisely target pigment under the skin.”

From cake frosting to groundbreaking research

Yellow No. 5 food coloring It's in everything from cereal, soda, spices, and cake frosting to lipstick, mouthwash, shampoo, dietary supplements, and house paint. It's also in some topical medications, but more research is needed before it can be used for human diagnostics, says Christopher J. Rowlands, PhD, a senior lecturer in the Department of Bioengineering at Imperial College London, UK, who studies biophotonic instrumentation to provide faster and clearer images of structures inside the body.

However, the findings could be useful for research. Commentary Publication year ScienceRowlands and his colleague Dr. John Gorecki, an photophysicist also at Imperial College London, point out that the dye could be an alternative to other optical clearing agents currently used in laboratories, such as glycerol, fructose, and acetic acid. The advantage is that the effect is reversible and it works at low concentrations with few side effects. This could expand the types of studies possible in laboratory animals, freeing researchers from having to rely on naturally transparent organisms such as nematodes and zebrafish.

The dye can also be combined with imaging techniques such as magnetic resonance imaging (MRI) and electron microscopy.

“All imaging technologies have strengths and weaknesses,” Rowlands says. “MRI has limited resolution and contrast but can view the entire body. Electron microscopes have excellent resolution but are limited in their compatibility with living tissue and penetration depth. Light microscopes have excellent cellular resolution, labeling capabilities, and biocompatibility but have a penetration depth of less than a millimeter. This clearing method will greatly advance optical imaging in medicine and biology.”

According to the statement, this discovery could lead to a tenfold improvement in the accuracy that depth imaging devices can achieve.

Brain research in particular will benefit: “In neurobiology in particular, the combination of multiphoton, optogenetics and tissue ablation could be very useful, potentially allowing us to record and control neural activity throughout the mouse brain,” he said.

Refraction, absorption, and The Invisible Man

The discovery of the dye finds distant echoes in H.G. Wells' 1897 novel. The Invisible ManIn the book, the serum makes the protagonist invisible by changing the light scattering, or refractive index (RI), of his cells to match that of the surrounding air.

Stanford engineers looked to the past for inspiration, but not to fiction. They turned to a concept called the Kramers-Kronig relation, first described in the 1920s. It's a mathematical principle that can be applied to the relationship between how light is refracted and absorbed by different materials. They also looked at Lorentz oscillations, which describe how electrons and atoms in molecules respond to light.

They reasoned that a light-absorbing compound could equalize differences in the light-scattering properties of proteins. Lipidsand moisture to make skin opaque.

So the search began. Postdoctoral researcher Zihao Ou, PhD, lead author of the study, began testing strong dyes to find a candidate. Tartrazine was the top candidate.

“We found that dye molecules are more effective at raising the refractive index of water than traditional index-matching agents, resulting in transparency at much lower concentrations,” Phuong said. “The fundamental physics explained by the Lorentz oscillator model and the Kramers-Kronig relation reveal that traditional index-matching agents, like fructose, are not as effective because they are not colored enough.”

What's next?

The dye is already used in products that people ingest or apply to their skin, but medical use is years away. In some people, tartrazine can cause skin and respiratory reactions.

The National Science Foundation, which funded the research, is a Activities The website states the following about the research: “The experiment involves coating slices of raw chicken breast with a tartrazine solution to make them transparent. For protection, the experiment should be carried out wearing a mask, eye protection, lab coat, and lab-quality nitrile gloves, according to the NSF.”

Meanwhile, Huong said his lab is searching for new compounds that could eliminate the redness seen in current experiments and improve visibility through the clear skin, as well as ways to induce cells to make the “clear” compounds themselves.

“We are investigating how cells can endogenously express powerful absorbing molecules to achieve genetically encoded tissue transparency in living animals,” he said.