In a groundbreaking development, a team of researchers from Tokyo Metropolitan University has created a new dye with the remarkable ability to strongly absorb second near-infrared (IR) radiation, transforming it into heat. This innovative dye, built upon a compound derived from the bile pigment family, represents a significant advancement in the field of medical imaging and treatment technologies. The researchers’ novel approach could pave the way for more effective therapies for deep tissue medical applications, particularly in cancer treatment and diagnosis.
The Challenge of Near-Infrared Light in Medical Applications
The second near-IR region of the electromagnetic spectrum (wavelengths between 1,000 and 1,700 nanometers) has long been of interest to medical scientists due to its unique properties. One of the key challenges in medical imaging and therapeutic applications is the limited ability of light to penetrate the human body, especially deeper tissues. However, light within the second near-IR range faces less scattering and absorption by biological tissues, making it particularly suitable for reaching deeper areas of the body with greater efficiency.
This transparency makes second near-IR light an ideal candidate for delivering energy into the body, whether for imaging purposes or in the context of therapeutic treatments. However, one major limitation in the application of this wavelength has been the lack of stable and efficient contrast agents that can effectively absorb light at these wavelengths.
The Breakthrough: Bilatriene and the Role of Rhodium and Iridium
The Tokyo Metropolitan University team, led by Associate Professor Masatoshi Ichida, set out to solve this issue by designing a new dye that could efficiently absorb second near-IR light. The research started with a compound called bilatriene, a dye from the bile pigment family, known for its ability to absorb light. Using a technique known as N-confusion chemistry, the team modified bilatriene’s molecular structure, creating a unique ring structure capable of binding metal ions like rhodium and iridium.
The resulting modified dye exhibited its most intense absorption at a wavelength of 1,600 nanometers, well within the second near-IR range. This strong absorption at a critical wavelength allows the dye to absorb light more effectively, converting it into heat that can then be utilized for medical treatments or imaging.
Exceptional Stability and Photostability
In addition to its strong absorption properties, the new dye showed exceptional photostability. Photostability is a crucial factor for materials used in medical applications, as it ensures that the dye remains intact and effective when exposed to light over extended periods. Many other contrast agents degrade when exposed to light, limiting their usefulness. The photostability of this new dye means it can be used repeatedly in medical applications without losing its efficacy.
Through detailed measurements and advanced modeling, including the use of density functional theory (DFT), the researchers were able to analyze how the dye reacts to magnetic fields and how the distribution of electrons in the molecule’s complex structure influences its light absorption properties. These calculations revealed that the unique configuration of the metal-binding molecule (known as a pi-radicaloid) produces absorption properties that are not achievable with existing compounds.
Potential Medical Applications: Deep Tissue Imaging and Therapy
One of the most promising applications of this new dye is in the field of photoacoustic imaging. Photoacoustic imaging is a powerful diagnostic tool used in cancer detection and treatment. In this technique, a contrast agent is injected into the body, and when it absorbs light, it generates heat. This heat causes tiny ultrasonic shocks that can be detected to create high-resolution images of tissue, or the heat itself can be used to destroy cancerous cells.
However, most contrast agents are more sensitive to light in the first near-IR region (700–1,000 nanometers), where scattering is stronger and energy delivery is less efficient. The second near-IR region, on the other hand, is less absorbed by tissue, allowing light to penetrate deeper and potentially deliver more energy. The new dye developed by the Tokyo team enables deeper and more efficient light penetration, which could improve the clarity of imaging and the effectiveness of heat delivery in therapies.
The ability to absorb light at 1,600 nanometers and convert it into heat could significantly enhance deep tissue therapies, particularly in cancer treatment, where precise targeting of tumor cells is critical. The dye’s photostability means that it can be used for longer periods without degradation, making it a reliable tool for long-term treatments or imaging sessions.
Broader Applications: Chemical Catalysis and More
While the immediate focus is on medical applications, the new dye also holds promise for other areas. The researchers suggest that this dye could be used in chemical catalysis, where its unique ability to absorb light at specific wavelengths may be applied to facilitate chemical reactions in industrial settings. Its exceptional photostability and strong absorption properties make it a versatile candidate for a variety of chemical processes that rely on light to initiate reactions.
Looking Ahead: The Future of Deep Tissue Medicine
The creation of this new dye marks a significant step forward in the field of deep tissue medicine. The Tokyo Metropolitan University team’s innovative approach to modifying bilatriene’s structure could open the door to new, more effective methods for cancer treatment, photoacoustic imaging, and other non-invasive diagnostic techniques. By enabling deeper penetration of light into tissues, the dye may improve both the accuracy and efficacy of medical therapies, particularly for conditions where traditional imaging and treatment methods struggle to reach.
Moreover, the dye’s development could lead to further advancements in the use of light-based therapies, which have the potential to revolutionize the way we approach treatments for a variety of medical conditions. As research in this area progresses, it is likely that we will see more applications for dyes and contrast agents that can operate effectively in the second near-IR range, offering a new frontier for non-invasive medical technologies.
Conclusion
The work by the Tokyo Metropolitan University team represents a major breakthrough in the development of advanced materials for medical imaging and therapy. By designing a dye that can efficiently absorb second near-IR light, they have created a powerful tool that could significantly enhance the effectiveness of deep tissue therapies and imaging techniques. With applications ranging from cancer diagnosis to photoacoustic therapies and chemical catalysis, this new dye has the potential to transform several areas of science and medicine. The ongoing research into this innovative compound will likely lead to even more advancements, opening up new possibilities for treating deep-seated diseases and improving patient outcomes.
Reference: Aninda Ghosh et al, Metal‐Bridging Cyclic Bilatriene Analogue Affords Stable π‐Radicaloid Dyes with Near‐Infrared II Absorption, Angewandte Chemie International Edition (2024). DOI: 10.1002/anie.202418751