The Guardian reveals a … well, a revealing discovery, that a common food dye can be used to make skin and muscle transparent enough for doctors to spot tumors or diagnose injuries:
Treated skin regained its normal colour when the dye was washed off, according to researchers at Stanford University, who believe the procedure opens up a host of applications in humans, from locating injuries and finding veins for drawing blood to monitoring digestive disorders and spotting tumours.
“Instead of relying on invasive biopsies, doctors might be able to diagnose deep-seated tumours by simply examining a person’s tissue without the need for invasive surgical removal,” said Dr Guosong Hong, a senior researcher on the project. “This technique could potentially make blood draws less painful by helping phlebotomists easily locate veins under the skin.”
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Dr Zihao Ou and his colleagues at Stanford theorised, counterintuitively, that particular dyes could make certain wavelengths of light pass more easily through skin and other tissues. Strongly absorbing dyes alter the refractive index of tissues that absorb them, allowing scientists to match the refractive indices of different tissues and suppress any scattering.In a series of experiments described in Science, the researchers show how a fresh chicken breast became transparent to red light minutes after being immersed in tartrazine solution, a yellow food dye used in US Doritos, SunnyD drink and other products. The dye reduced light scattering inside the tissue, allowing the rays to penetrate more deeply.
The team then smeared the yellow dye on a mouse’s underbelly, making the abdominal skin see-through and revealing the rodent’s intestines and organs. In another experiment, they applied dye to a mouse’s shaved head and, with a technique called laser speckle contrast imaging, saw blood vessels in the animal’s brain.
“The most surprising part of this study is that we usually expect dye molecules to make things less transparent. For example, if you mix blue pen ink in water, the more ink you add, the less light can pass through the water,” Hong said. “In our experiment, when we dissolve tartrazine in an opaque material like muscle or skin, which normally scatters light, the more tartrazine we add, the clearer the material becomes. But only in the red part of the light spectrum. This goes against what we typically expect with dyes.”
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There are some photos at the link, and you can read more of the Stanford experiments here, in Science.