Dr Michelle Dickinson: nanotechnologist on food dye creating see-through mice

The Sunday Session with Francesca Rudkin

Did you ever dream you had X-ray vision when you were a kid? While that might sound like something from comic books, new research published in Science this week could bring us one step closer to making it a reality.

Scientists have found a way to see inside the bodies of living animals without surgery by using a surprising tool: a food dye that is common in America. This breakthrough discovery revealed that the dye, known as tartrazine, can make skin, muscles, and connective tissues temporarily see-through!

Tartrazine is a yellow food dye commonly found in products like Doritos and other snacks in the U.S. The dye doesn’t just colour food; it has an unexpected ability to change how light moves through tissues. Normally, light entering biological tissue scatters because of the different structures inside the body, like fatty membranes and cell nuclei. These structures have a different refractive index from the air around them, which is why light doesn’t travel smoothly through our skin and other tissues.

This scattering effect is what keeps us from seeing through our skin - or anyone else's. However, in this study, tartrazine was found to reduce the amount of light scattering inside tissue, allowing light to penetrate more deeply. The result? Scientists could see through the skin of living animals.

In a fascinating experiment using mice, researchers applied tartrazine to the animals' skin. When rubbed onto the belly, the dye allowed scientists to clearly see the liver, intestines, and bladder beneath the skin. When applied to the scalp, they could even observe blood vessels in the brain!

Even more amazing, the skin returned to its normal colour after the dye was washed off, meaning the effect wasn’t permanent.

To understand how this works, think about what happens when you place a pencil in a glass of water. The pencil appears bent or distorted because light behaves differently when it passes through water compared to air. This is due to something called the refractive index, which measures how much light bends when it passes through different materials. The same principle applies when light passes through biological tissues like skin.

Under normal circumstances, biological tissues scatter light, making it impossible to see through them. The dye used in this study helps certain wavelengths of light pass through tissues more easily, reducing that scattering effect.

While this discovery is ground-breaking, it’s not perfect. The effect is limited by how deeply the dye can penetrate into tissues. For now, the transparency only works on surface-level tissues. However, the scientists are already developing techniques like micro-needling and injections to allow the dye to reach deeper layers of skin and tissue.

Although this study was conducted on mice, the potential applications for humans are enormous. Imagine doctors being able to visualize organs, blood vessels, and deep tissues without invasive surgery. This technology could revolutionise fields like diagnostics, allowing for real-time monitoring of the body’s internal structures with minimal risk to the patient.

The future possibilities are exciting. With further research, this dye technique could become a powerful tool for non-invasive medical imaging, bringing us closer to a world where X-ray vision isn’t just a superpower - it’s science.

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