New Dye Advances Photothermal Cancer Treatment and Imaging

The second near-infrared region of the electromagnetic spectrum (1,000 – 1,700 nanometers) offers significant advantages in medical science. Unlike shorter wavelengths, light in this range penetrates biological tissue more deeply and with less scattering. This transparency makes NIR-II ideal for medical imaging and therapies, including photoacoustic imaging. In this technique, light-induced heat generates ultrasonic waves that can either reveal detailed images or deliver targeted cancer treatments.   

However, the effectiveness of such techniques relies on contrast agents capable of absorbing light in the NIR-II range while remaining stable under exposure. Most existing agents are optimized for the first near-IR range (700 – 1,000 nanometers), which limits their efficiency for deep tissue applications.   

To address this limitation, the research team led by Associate Professor Masatoshi Ichida developed a compound from the bile pigment family, bilatriene. Using a method known as N-confusion chemistry, they modified bilatriene to incorporate metal ions, specifically rhodium and iridium. The resulting dye exhibited strong absorption at a wavelength of 1,600 nanometers, well within the second near-IR region.   

This absorption capability was paired with exceptional photostability, ensuring that the compound remains intact under light exposure. Detailed measurements and computational modeling using density functional theory (DFT) revealed the unique electron distribution in the dye’s structure, which enables its remarkable absorption properties.   

The ability of this dye to absorb second near-IR radiation paves the way for more efficient energy delivery in medical imaging and therapies. Because NIR-II wavelengths penetrate tissues more effectively, the dye could enhance photoacoustic imaging by providing clearer visuals of internal structures. Additionally, its heat-generating properties may improve the precision and efficacy of photothermal cancer treatments, minimizing damage to surrounding healthy tissues.   

MEDICA-tradefair.com; Source: Tokyo Metropolitan University