New Dye offers a breakthrough in depth imaging and cancer therapy

New Dye offers a breakthrough in depth imaging and cancer therapy

Researchers at Tokyo Metropolitan University have developed a new dye that can strongly absorb second near-IR radiation and convert it into heat. Starting with a dye from the bile pigment family, they designed a unique ring structure that can bind rhodium and iridium. Measurements and modeling showed strong second near-IR absorptions and exceptional photostability. Second near-ir waves easily penetrate human tissue; The new dye can be used in deep tissue therapies and imaging.

The second near-IR region of the electromagnetic spectrum (1000-1700 nanometers) is a potentially important wavelength range for medical science. In this area, light is not as strongly scattered or absorbed by biological tissue. This transparency makes it ideal for delivering energy to deeper parts of the body, whether for imaging or treatments. An important example of such therapy is photoacoustic imaging in cancer diagnosis and treatment. When a contrast agent injected into the body is injected with light, it emits heat, creating tiny ultrasound shocks that can either be detected for imaging or damage cancer cells themselves.

The effectiveness of this approach depends on the availability of stable contrast agents that can efficiently absorb light at these wavelengths. However, the majority of contrast agents are more sensitive in the first near-IR region (700-1000 nanometers), where scattering effects are stronger and energy delivery is less efficient.

Now a team of researchers led by Associate Professor Masatoshi Ichida from Tokyo Metropolitan University have developed a new chemical compound that overcomes the heel of this Achilles. Starting with a dye from the bile pigment family called bilatriene, they used a method known as N-confusion chemistry to alter the ring structure of bilatriene to accept binding of metal ions. In their recent work, they successfully incorporated rhodium and indium ions into the ring via nitrogen atoms.

The team's new dye showed its strongest light absorption at a wavelength of 1600 nanometers under normal conditions, which is good in the second near-IR region. It has also been shown to be highly photostable, meaning it does not break apart easily when exposed to light. Detailed measurements of how the molecule responds to magnetic fields and numerical calculations using density functional theory (DFT) showed how the unique distribution of electrons in a cloud encompassing the entire, complicated structure of the metal binding molecule (also known as a PI-radicaloid) resulted in absorptions not possible in existing, similar compounds.

Because the second near-IR is not as strongly absorbed by tissues, regions sensitized with the dye can be more exposed to light, allowing for clearer imaging and better delivery of heat for therapies. The team hopes their molecule will open the door to new approaches to deep tissue medicine, as well as more general applications to chemical catalysis.

This work was supported by JSPS Grant Numbers JP20H00406 and JP22K19937, JST Presto Grant Number JPMJPR2103, Izumi Science and Technology Foundation, Advanced Research Infrastructure for Materials and Nanotechnology in Japan (Arim) of the Ministry of Education, Sports, Sports, Science, Science and Technology (MEXT) Under Proposal Number JPMXP1222ms1802, the Cooperative Research Program from NJRC Mater. & Dev. And a Tokyo Global Partner Fellowship from Tokyo Metropolitan University.

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