South SFV Today

Stanford researchers have developed a technique to make mouse skin transparent using an FDA-approved food dye, as detailed in their study published on September 5 in Science. This method allows scientists to see internal organs without making incisions and can be reversed by rinsing the skin with water.

Guosong Hong, assistant professor of materials science and engineering and senior author of the paper, stated, “As soon as we rinsed and massaged the skin with water, the effect was reversed within minutes. It’s a stunning result.”

The research involves applying a solution of red tartrazine, also known as FD&C Yellow 5, onto the mouse's abdomen, scalp, and hindlimb. The dye alters the refractive index of water in the tissue to match that of lipids at a specific wavelength (red), reducing light scattering and making the skin appear transparent.

This technique builds on decades-old equations known as Kramers-Kronig relations that describe the relationship between absorption and refractive index. Other light-absorbing molecules were also found to have similar effects.

Researchers could observe functioning internal organs such as the liver, small intestine, cecum, bladder, blood flow in the brain, and muscle fibers without special equipment. Importantly, this transparency did not permanently alter the subject's skin.

Mark Brongersma, co-author and professor of materials science and engineering at Stanford University remarked on the interdisciplinary nature of this project: “Stanford is the perfect place for such a multifaceted project that brings together experts in materials science, neuroscience, biology, applied physics, and optics.”

Although currently tested only on animals, this non-invasive technique could offer significant biological and diagnostic benefits if translated to humans. Hong noted potential applications like melanoma testing without biopsies or improving laser tattoo removal precision.

“This could have an impact on health care and prevent people from undergoing invasive kinds of testing,” said Hong. “If we could just look at what’s going on under the skin instead of cutting into it or using radiation to get a less than clear look, we could change the way we see the human body.”

The research team includes multiple members from Stanford’s Department of Materials Science Engineering and Wu Tsai Neurosciences Institute among others. The study received support from various institutions including NIH, NSF, Air Force Office of Scientific Research among others.

A disclaimer notes that while promising results were seen in mice studies; human testing has not been conducted yet. Handling dyes should be done with caution due to potential harm.

For further inquiries:

Jill Wu

School of Engineering

jillwu@stanford.edu

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