Researchers at Stanford University have developed a novel method to visualise internal organs by rendering overlying tissues transparent with a food-safe dye.
Stanford University’s research team has discovered a way to make internal organs visible by using a food-safe dye to render overlying tissues transparent. This approach, published in the September 6, 2024, issue of Science, was shown to be reversible in animal tests and may significantly impact various medical diagnostics. Applications could include locating injuries, monitoring digestive disorders, and detecting cancers.
“Our technology could improve procedures such as blood draws and make laser-based treatments, like tattoo removal and cancer therapies, more effective,” stated Guosong Hong, an assistant professor of materials science and engineering at Stanford University. Hong, a U.S. National Science Foundation (NSF) CAREER grantee, co-led the research. By enhancing light penetration, this technique could allow for the early detection and treatment of cancers that are currently challenging to address.
The Science Behind Transparency
To achieve transparency, the researchers focused on how light interacts with biological tissues. Understanding light scattering and refraction, where light changes direction as it moves between different materials, was crucial. Biological tissues consist of components with varying refractive indices, causing light to scatter and creating opacity. To counteract this, the team sought to match these refractive indices, allowing light to pass through tissues without scattering.
The dye that proved effective was tartrazine, a common food dye also known as FD & C Yellow 5. When dissolved in water and absorbed by tissues, tartrazine aligns the refractive indices of cellular fluids and proteins, resulting in transparency. Initial experiments involved applying tartrazine to chicken breast slices, successfully rendering them transparent. Further tests on live mice showed that the dye could temporarily make skin transparent, revealing underlying structures like blood vessels and internal organ movements. The transparency was reversible, with tissues regaining opacity after the dye was rinsed off and any excess dye naturally excreted within 48 hours.
Bridging Physics and Medicine
The development of this dye-based transparency technique is rooted in fundamental physics. Drawing from concepts in optics dating back to the 1970s and 1980s, such as the Kramers-Kronig relations and Lorentz oscillation, the researchers were able to predict the behaviour of light-absorbing dyes. These principles, traditionally studied for their applications in physics, were adapted to suit medical needs.
Lead researcher Zihao Ou, a postdoctoral fellow, meticulously tested a range of dyes to find those with optimal optical properties. The success of this project also hinged on using an ellipsometer, an instrument typically employed in semiconductor manufacturing, to analyse the optical properties of the dyes. NSF Program Officer Richard Nash noted the importance of access to basic and advanced tools, highlighting how unexpected applications of familiar technologies can lead to significant scientific advancements.
Looking Ahead
This innovative technique, combining fundamental optics with practical medical applications, is set to open new avenues in the field of biomedical imaging. By enabling deeper and more detailed visualisation of internal structures, the use of tartrazine and similar dyes could become a cornerstone of future diagnostic and therapeutic procedures.
NSF’s ongoing support was instrumental in the success of this research. “The flexibility and encouragement from the NSF awards were crucial in keeping me on track and allowed me the freedom to explore new and uncharted territories in my field,” Hong reflected, underscoring the significance of adaptable funding in scientific innovation.
For more information on this research, please read the original paper “Achieving optical transparency in live animals with absorbing molecules“, in Science.