Scientists from Columbia University, in collaboration with Harvard researchers, have succeeded in developing a chemical process to convert visible light into infrared energy, allowing harmless radiation to penetrate into living tissue and other materials without the damage caused by exposure to light from high intensity.
Their research is published in the January 17 issue of Nature.
"The findings are exciting because we were able to perform a series of complex chemical transformations that typically require high-energy, visible light using a non-invasive, infrared light source," said Tomislav Rovis, professor of chemistry at Columbia and co-author of the study. "You can imagine many potential applications where barriers impede control over matter, for example because the research is promising to improve the reach and effectiveness of photodynamic therapy, whose full potential for cancer management still needs to be realized."
The team, including Luis M. Campos, Associate Professor of Chemistry at Columbia, and Daniel M. Congreve of the Rowland Institute at Harvard, conducted a series of experiments with small amounts of a new compound that, when stimulated by light, mediate the transfer of electrons between molecules that would otherwise react more slowly or not at all.
Their approach, known as triplet fusion upconversion, includes a series of processes that essentially unite two infrared photons into a single visible light photon. Most technologies only absorb visible light, so that the rest of the solar spectrum is lost. The upconversion of the triplet fusion can harvest the infrared light with low energy and convert it into light that is then absorbed by the solar panels. Visible light is also easily reflected by many surfaces, while infrared light has longer wavelengths that can penetrate dense materials.
"With this technology we were able to fine-tune infrared light to the necessary longer wavelengths, allowing us to go non-invasively through a wide range of barriers, such as paper, plastic molds, blood and tissue," said Campos. The researchers even pulsed lightly through two strips of bacon wrapped around a bottle
Scientists have long tried to solve the problem of visible visible light entering the skin and into the blood without damaging internal organs or healthy tissue. Photodynamic therapy (PDT), used to treat some cancers, uses a special drug, called a photosensitizer, which is activated by light to produce a highly reactive form of oxygen that can kill or inhibit the growth of cancer cells.
Current photodynamic therapy is limited to the treatment of localized or superficial cancers. "This new technology could bring PDT into parts of the body that were previously inaccessible," said Rovis.
"Instead of poisoning the entire body with a drug that causes the death of malignant cells and healthy cells, a non-toxic drug in combination with infrared light can selectively attack the tumor site and irradiate cancer cells."
The technology can have far-reaching consequences. Infrared light therapy can be an aid in the treatment of a number of diseases and conditions, including traumatic brain injury, damaged nerves and spinal cord, hearing loss and cancer.
Other possible applications include remote management of production of solar power production on solar energy and data storage, drug development, sensors, food safety methods, moldable composites with bone mimics and processing of microelectronic components.
The researchers are currently testing photon-upconversion technologies in complementary biological systems. "This opens up unprecedented opportunities to change the way light interacts with living organisms," said Campos. "In fact, we now use up-conversion techniques for tissue engineering and drug delivery."
Upconversion fluorescence in metal organic frameworks
Benjamin D. Ravetz et al, Photoredox catalysis using infrared light via triplet fusion upconversion, Nature (2019). DOI: 10.1038 / s41586-018-0835-2