Researchers have unveiled a novel application for a common food dye, demonstrating that it can temporarily render skin, muscle, and connective tissues transparent. This breakthrough allows for clearer visualization of internal structures in living animals, such as the liver, intestines, and bladder, when the dye is applied to their skin.
In experiments conducted by Stanford University researchers, applying the dye to a mouse’s abdomen made its internal organs visible through the skin. Similarly, when used on the mouse’s scalp, the dye allowed scientists to observe blood vessels in the brain.
The procedure, detailed in Science, shows that the dye’s effects are reversible; the treated skin returns to its normal color once the dye is washed off. Dr. Guosong Hong, a senior researcher on the project, suggests that this technique could have significant medical applications, including easier detection of injuries, less painful blood draws, and improved monitoring of digestive disorders and tumors.
This development echoes the fictional concept of invisibility explored by H.G. Wells in his 1897 novel, The Invisible Man. In the novel, Wells describes a method for achieving invisibility by matching an object’s refractive index to that of the surrounding air. Similarly, the researchers’ approach involves modifying the refractive index of tissues with the dye to reduce light scattering and enhance transparency.
Biological tissues scatter light because their internal structures, such as cell membranes and nuclei, have varying refractive indices. This scattering causes tissues to appear opaque. By using dyes that alter the refractive index, researchers can make light pass more smoothly through tissues, reducing opacity. For example, the study demonstrated that tartrazine, a yellow food dye used in products like Doritos and SunnyD, made a chicken breast transparent to red light within minutes.
In their experiments, the team first immersed a chicken breast in a tartrazine solution, revealing the tissue’s internal structure to red light. They then applied the dye to a mouse’s abdomen and scalp, making the skin translucent and enabling the observation of internal organs and blood vessels.
Dr. Zihao Ou, a colleague of Hong, noted the surprising results: “Typically, we expect dyes to reduce transparency. For instance, adding ink to water decreases light transmission. However, our study showed that adding tartrazine to opaque tissues like muscle or skin actually increased their clarity, but only in the red part of the spectrum.”
The transparency effect is contingent on the depth of dye penetration. Although the technique has yet to be tested on humans, and safety concerns regarding injections need to be addressed, the researchers envision potential applications including microneedle patches for deeper dye delivery.
This advancement could also impact scientific research. Currently, studies often rely on transparent animals like zebrafish to observe disease progression. The new transparency dyes could expand research possibilities to a broader range of species.
In a commentary, Christopher Rowlands and Jon Gorecki from Imperial College London expressed excitement about the potential of this technique. They believe it could significantly enhance imaging capabilities, allowing for detailed observations of entire brains or detection of tumors beneath thick tissues. They note that H.G. Wells, who once studied biology under T.H. Huxley, would likely appreciate this scientific innovation.