**Stanford Researchers Innovate Reversible Skin Clarity Using Doritos Dye**
A major hurdle in medical imaging is the challenge of seeing through opaque tissues like skin. This limitation necessitates the use of technologies such as ultrasonography, magnetic resonance imaging (MRI), and X-rays for visualizing internal organs and structures. Although there are chemical solutions that can render tissues transparent, like acrylamide or tetrahydrofuran, they are seldom employed in living organisms due to their toxicity or the potential to dissolve vital biomolecules.
Nevertheless, a significant advancement has been achieved by a group of scientists at Stanford University. They have identified a method to temporarily render skin transparent without causing harm. The unexpected agent responsible for this breakthrough? Tartrazine, a yellow-orange food coloring commonly referred to as FD&C Yellow 5, often found in products such as Doritos.
### The Science of Clarity
The inability to see through skin stems from its intricate structure. Skin comprises various elements, including aqueous substances such as cell interiors and fluids, alongside proteins and lipids. These constituents possess differing refractive indices, which quantify how much light slows down as it passes through a medium. Aqueous elements have a low refractive index, whereas proteins and lipids have a high one. As light traverses the skin, it continually bends at the interfaces between these materials, resulting in scattering. This scattering obstructs light from penetrating deeply and returning, rendering the skin opaque.
To achieve skin transparency, the objective is to diminish light scattering by creating a more uniform refractive index. This is where tartrazine becomes crucial.
### An Unexpected Finding
Guosong Hong, an assistant professor of materials science and engineering at Stanford and the study’s senior author, expressed surprise at the outcomes. “The most unexpected aspect of this study is our usual assumption that dye molecules reduce transparency,” Hong noted. “For instance, adding blue pen ink to water results in decreased light transmission. However, in our tests, dissolving tartrazine in an opaque medium like muscle or skin, which typically scatters light, surprisingly increased clarity with more tartrazine. This contradicts our conventional expectations regarding dyes.”
### Crafting a “Clarity Solution”
The team created a “clarity solution” by dissolving tartrazine in an aqueous mixture. This solution effectively minimized the refractive index disparity between water and lipids in the skin. The researchers initially applied the solution to polymer gels designed to mimic light-scattering tissue properties. Following successful outcomes, they proceeded with more complicated models, including thinly sliced chicken breasts and live mice.
Upon application to a mouse’s skin, the solution began to take effect within minutes. When massaged into the shaved scalp of a mouse, it enabled researchers to visualize cerebral blood vessels using laser speckle contrast imaging, a method typically requiring scalp removal. When applied to the abdomen, the solution rendered internal organs, like the liver, bladder, and small intestine, visible to the naked eye. Importantly, the clarity effect was reversible—washing off the solution with water restored the skin’s opacity.
### Challenges and Constraints
Despite promising results, several challenges were encountered. One issue was that tartrazine absorbed most light at wavelengths around 257 and 428 nanometers, allowing visualization of violet and blue shades. However, it displayed minimal absorption above 600 nanometers, leading to a red hue when observing the transparent skin. Additionally, the depth of penetration posed a challenge. The solution worked efficiently on thinner skin areas but had difficulty penetrating thicker skin.
Moreover, the solution’s formulation was not universally applicable. The team needed to identify a chemical that corresponded to the refractive index of lipids in water, requiring extensive trial and error. Individual variations among mice also complicated the development of a standardized solution.
### Tackling Challenges: Tattoos and Needles
In response to the issues related to penetrating thicker skin, researchers contemplated more invasive approaches. “Using microneedle patch applicators or subcutaneous injections could facilitate the delivery of the molecules through thicker skin layers,” Hong proposed. Regarding the red tint, Hong’s lab is actively researching alternative dyes that absorb light in the near-ultraviolet spectrum, which could help reduce the red tone and enhance clarity.
Hong also pointed out potential human applications for this technology, although testing has only been conducted on animals thus far. If adapted successfully for human use, the clarity solution could transform areas such as biology, diagnostics, and even cosmetics. For instance, it could enable non-invasive assessment of deep-seated tumors, simplify vein location, thereby reducing stress during blood tests, and improve laser tattoo removal by allowing precise targeting of pigments beneath the skin.
### Warning: Don’t Attempt This at Home
