- A new technique, called triplet fusion upconversion, fuses two infrared photons into one visible light photon.
- It allows scientists to use infrared light to penetrate blood and skin without damaging healthy tissue or internal organs.
Photoredox catalysis — a branch of catalysis that utilizes light energy to accelerate a chemical reaction through single-electron transfer events — have made it possible to accomplish several polymerizations, synthetic transformations, and surface modifications.
Such reactions require visible- or ultraviolet-light stimuli, however, using visible-light irradiation is quite a complex task. It has its own challenges, for instance, visible light penetration through a variety of reaction media is very low, which causes issues in large-scale reactions.
Also, reactants could compete with photocatalysts to absorb the incident light, which further limits the scope of the reactions. One can overcome these issues by using near-infrared light that has higher penetration depth through several media, especially biological tissue.
Recently, a research team at Harvard University and Columbia University developed a chemical process to transform visible light into infrared light, allowing harmless radiation to penetrate a wide range of materials, including living tissue, without damaging them.
Triplet Fusion Upconversion
In this study, researchers performed numerous complex chemical transformations (that require high-intensity, visible light) using an infrared light source. More specifically, they conducted a series of experiments with a small number of novel materials that, in presence of light, trigger electron transfer between molecules, which otherwise wouldn’t react or react too slow.
Their new methodology called triplet fusion upconversion, includes a series of processes that fuses 2 infrared photons into 1 visible light photon.
Reference: Nature | doi:10.1038/s41586-018-0835-2 | Columbia University
While most of the techniques only capture light in the visible spectrum (remaining solar spectrum is wasted), the new approach harvests low infrared energy and transforms it into light energy, which can then be fed to solar panels. Many surfaces can reflect visible light, but since infrared has longer wavelengths, it can penetrate thick or dense compounds.
Billions of molecular lightbulbs use infrared photons to produce visible light | Credit: Melissa Ann Ashley /Columbia University
The technology helped researchers to configure the infrared light in a way that it can pass through a variety of barriers, including blood, tissue and plastic molds. In fact, it can penetrate blood and skin without damaging healthy tissue or internal organs.
The technology can also bring photodynamic therapy — a treatment that uses photosensitizer and a particular type of light to kill cancer cells — into parts of the body that were previously unreachable. Instead of contaminating the whole body with medicines, drugs fused with infrared light could be used to target the specific tumor site.
Moreover, infrared light therapy could be instrumental in diagnosing and treating various conditions, such as damaged spinal cords and brain injury. Other promising applications include processing microelectronic modules, sensors, drug development, and remote management of chemical storage of solar power generation.
The research team is currently trying to employ their technology in drug delivery and tissue engineering. If successful, this may completely change the way photons interact with living organisms.