Unique Materials Convert Visible into Infrared Light, Paving Way for Photodynamic Therapy and Drug Development

Researchers from Columbia University, in partnership with scientists from Harvard, have been successful in developing a chemical process to turn visible light into infrared energy, allowing innocuous radiation to enter living tissue and other materials without causing damage because of high-intensity light exposure.

Billions of molecular lightbulbs, powered by invisible infrared photons, generate visible light. (Image credit - Melissa Ann Ashley)

Their study is published in Nature (January 17 issue).

The findings are exciting because we were able to perform a series of complex chemical transformations that usually require high-energy, visible light using a noninvasive, infrared light source. One can imagine many potential applications where barriers are in the way to controlling matter. For example, the research holds promise for enhancing the reach and effectiveness of photodynamic therapy, whose full potential for managing cancer has yet to be realized.

Tomislav Rovis, Study Co-Author and Professor of Chemistry, Columbia University

The team, which includes Luis M. Campos, associate professor of chemistry at Columbia, and Daniel M. Congreve of the Rowland Institute at Harvard, conducted a series of experiments using small amounts of a novel compound that, when activated by light, can mediate the transfer of electrons between molecules that otherwise would react more gradually or not at all.

Their method, known as triplet fusion upconversion, comprises a chain of processes that basically fuses two infrared photons into a single visible light photon. A majority of technologies only trap visible light, meaning the rest of the solar spectrum gets wasted. Triplet fusion upconversion can harvest low-energy infrared light and change it to light that is then absorbed by the solar panels. Visible light is also easily reflected by numerous surfaces, while infrared light comprises longer wavelengths that can enter dense materials.

“With this technology, we were able to fine-tune infrared light to the necessary, longer wavelengths that allowed us to noninvasively pass through a wide range of barriers, such as paper, plastic molds, blood, and tissue,” Campos said. Light was even pulsed through two strips of bacon wrapped around a flask.

Researchers for long have attempted to solve the issue of how to make visible light penetrate skin and blood without harming healthy tissue or internal organs. Photodynamic therapy (PDT), used to treat some cancers, utilizes a special drug, called a photosensitizer, that is stimulated by light to create an extremely reactive form of oxygen that is able to destroy or hinder the growth of cancer cells.

Existing photodynamic therapy is restricted to the treatment of surface or localized cancers. “This new technology could bring PDT into areas of the body that were previously inaccessible,” Rovis said.

Rather than poisoning the entire body with a drug that causes the death of malignant cells and healthy cells, a nontoxic drug combined with infrared light could selectively target the tumor site and irradiate cancer cells.

Tomislav Rovis, Study Co-Author and Professor of Chemistry, Columbia University

The technology could have widespread impact. Infrared light therapy may be key in treating several diseases and conditions, including damaged nerves, traumatic brain injury, and spinal cords, hearing loss, as well as cancer.

Other potential applications include remote management of chemical storage solar power production and data storage, moldable bone-mimic composites, food safety methods, sensors, drug development, and processing microelectronic components.

The scientists are presently testing photon-upconversion technologies besides biological systems.

This opens up unprecedented opportunities to change the way light interacts with living organisms. In fact, right now we are employing upconversion techniques for tissue engineering and drug delivery.

Luis M. Campos, Associate Professor of Chemistry, Columbia University

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