Scientists at Stanford University have developed an innovative method that makes human body tissues transparent to visible light. The breakthrough could lead to major advances in medical diagnostics, including detecting injuries, monitoring digestive disorders and detecting cancers.

The new technology relies on the topical application of a safe dye that has been shown to be reversible in animal tests. Researchers from Stanford University published their results in the journal Science, describing their approach that involved predicting the interaction of light with dyed biological tissues.

“In the future, this technology could make veins more visible for blood sampling, facilitate laser removal of tattoos, or aid in early detection and treatment of cancer,” said Gosong Hong, associate professor of materials science and engineering at Stanford University School of Medicine, who helped lead the study.

The researchers developed a method that required a deep understanding of the light scattering and refraction processes to predict the interaction of light with stained biological tissues. They found that the dyes that absorb light most efficiently may also be very efficient in the uniform direction of light due to their large refractive index.

“For example, some treatments use lasers to destroy cancerous and pre-cancerous cells, but these are limited to areas close to the skin surface. This technique can increase the penetration of the method,” Hong noted.

One dye that the researchers predicted would be particularly effective was tartrazine, a food dye better known as FD&C Yellow 5. It scatters light, providing transparency.

The researchers tested their predictions on thinly sliced ​​chicken breasts and mice. They found that when a tartrazine solution was applied to the scalp of the mice, it became transparent, allowing blood vessels in the brain to be seen. A similar result was obtained when the solution was applied to the stomachs of mice, allowing observation of intestinal contractions and movements caused by heartbeat and breathing.

The technique allowed for micrometer-scale features and even improved microscopic observations. When the dye was washed away, tissues rapidly returned to normal opacity. Tartrazine appeared to have no long-term effects and any excess was excreted in waste within 48 hours.

The researchers suspect that using the dye will lead to an even deeper understanding of organisms, with implications for both biology and medicine. The project began as a study of the interaction of microwave radiation with biological tissues, but ultimately led to the development of a new technology that could be widely used in medicine.

Using methods based on fundamental physics, the researchers hope that their approach will lead to a new line of research in matching dyes to biological tissues based on optical properties, potentially leading to a wide range of medical applications.

“Advanced research facilities are constantly trying to find the right balance between providing access to essential tools and expertise while making room for new, larger, and more powerful instruments. While a simple “workhorse” like an ellipsometer rarely makes headlines, it can still play a crucial role when used for an unusual purpose, as in this case. Open access to such tools is essential for groundbreaking discoveries because they can be used in new ways to generate fundamental insights about scientific phenomena,” said Richard Nash, NSF Program Manager for NNCI.

As an optician myself, I am amazed at how much they have gained by leveraging the Kramers-Koenig relationship. Every optics student knows all this, but this team used the equation to figure out how an absorbing dye can make skin transparent. “Hong has taken a step in a bold new direction that is a great example of how fundamental knowledge in optics can be used to create new technologies, including in the biomedical field,” said Adam Wax, NSF program director who worked on Hong’s work.