Yellow food coloring could make living tissue transparent – ​​these methods could in the future improve cancer treatment, blood sampling and even tattoo removal

Why is your body not transparent? Animals like jellyfish, Zebrafish and a few Glass frogs have transparent bodies. But most mammals, including humans, should not transparent.

While the concept of ​​a transparent body could appear strange and even a little bit scary, it could actually be very helpful for doctors. If our bodies were transparent, doctors could easily see inside to diagnose diseases in organs just like the liver, spleen, and brain. They wouldn't need invasive procedures like biopsies or expensive equipment like CT scanners and MRIs.

I’m a materials scientistand my team and I are working on how latest materials can aid biomedicine. My colleagues and I wondered whether it was possible to make living tissue temporarily transparent to assist medical treatments and other applications.

We found that by dissolving certain dye molecules, including a food coloring commonly utilized in snacks called FD&C Yellow 5in water, we will change the way in which light travels through the water. We have used this phenomenon to make organic tissue – specifically the skinny skin of mice – transparent in our study, published in September 2024 in Science.

Refractive indices

Our bodies, like those of most mammals, should not transparent, mainly due to the way in which light interacts with our tissues. Normally, light travels in a straight line through the air. But when light hits the human body, it doesn't travel very far before it’s scattered. The light bounces off in several directions as an alternative of passing through us in a straight line. If light passed through us without scattering, our tissues could be transparent.

This spread This is because human tissue is made up of many alternative components, including water, fats and proteins. Each of those components slows down light otherwise, a property generally known as Refractive index.

For example, water has a refractive index of about 1.33while fats and proteins have a better refractive index of about 1.45 within the visible spectrumLight subsequently moves more slowly in lipids than in water.

The key to transparency of living tissue could be to cut back the differences within the propagation of sunshine through different parts of the tissue – especially between water, fats and proteins.

Kramers-Kronig relationships

A principle of physics generally known as Kramers-Kronig relationships explains how a cloth that absorbs more light of 1 color, for instance blue, changes the movement of sunshine of one other color, for instance red, through the fabric because of this increased absorption. Kramers-Kronig relations state that the colours of sunshine should not independent of one another, but are connected to one another.

FD&C Yellow 5 strongly absorbs blue light, which supplies it its characteristic orange-red color when dissolved in water. This happens since the blue a part of the sunshine is absorbed, leaving only the orange-red part visible. Due to Kramers-Kronig relationships, this absorption of blue light increases the refractive index of water for red light. The refractive index of water increases from 1.33 to match that of fats and proteins, which is about 1.45.

When the refractive indices match, red light isn’t any longer scattered as much. It moves in water in the identical way that it does in fats in tissue. The entire tissue subsequently appears as a single, uniform material. This process could make the tissue appear transparent, regardless that it is often opaque.

Making fabric transparent

My research team implemented this concept in an experiment using a scatter phantom, a cloth designed to mimic the opacity of human skin. When we added more FD&C Yellow 5 dye to the phantom, it became more orange-red, just as expected.

But something else happened. It became more transparent to red light. This increased transparency allowed us to see the grid pattern on the table beneath the phantom.

We then decided to check this concept on a bit of chicken breast from the supermarket. Unless it’s sliced ​​very thinly, chicken meat often looks opaque.

When we placed the chicken breast in an answer containing FD&C Yellow 5 dye, something amazing happened. It became more transparent, allowing us to obviously see a Stanford shield attached underneath.

Finally, we used this concept to make a mouse's skin optically transparent. We applied the dye FD&C Yellow 5 to different parts of the mouse's body. When we applied it to the mouse's scalp, we could see the blood vessels in its brain. When we applied it to the mouse's abdomen, we could see its intestines. When we applied it to the mouse's limbs, we could see its muscle fibers.

All that was required for this experiment was gently massaging a dye solution into the mouse's skin and a little bit patience.

This process is non-invasive because it doesn’t require tissue removal or surgery and the skin will return to its normal opacity when you rinse the colour off with water. Although it’s a captivating technique, we strongly advise against trying this yourself.

Although the usage of Yellow 5 is approved by the FDA, some people have raised concerns about its potential Health risksThese include allergic reactions – particularly in asthmatics – hyperactivity in children and possible links to cancer. But researchers must do more testing to find out if there are any dangers.

Future uses

So what could this approach be used for? Currently, it really works best on very thin layers of skin, like that of a mouse.

Unfortunately, human skin is far thicker, so this method will not be quite ready for practical use on humans. Additionally, the red color of the dye implies that the colour balance will not be quite right and the transparency will not be perfect across your complete surface. entire visible spectrumThe dye still blocks blue light.

My colleagues and I are working to enhance this method to make it more practical for human tissue. We are also attempting to direct the absorption of the dye towards the Ultraviolet spectrumwhich might create a more balanced transparency effect across all visible colours.

In the longer term, this technology could make veins more visible, making venipuncture – the practice of drawing blood or injecting fluids using a needle – easier, especially in older patients with difficult-to-see veins.

It could also help to Early detection of skin cancerexpand Light irradiation into deep tissue for photodynamic And Photothermal therapies and simplify Laser tattoo removal.

In photodynamic and photothermal therapies, doctors use a laser to kill cancer cells and precancerous lesions. However, the laser light only penetrates the tissue to a certain extent, so these therapies should not yet suitable for organs situated deeper within the body.

All of those applications may gain advantage from a reversible, on-demand transparency window within the body.