Picture a cancer treatment that targets a specific group of tissues, using nothing but light and metal compounds. The treatment doesn’t affect surrounding healthy cells, and the patient doesn’t have any notable side effects.
This treatment exists today. Called photodynamic therapy, it’s used primarily to treat cancers that are near an accessible surface of the body. And spectroscopy is front and center in the development of the technology.
You need three things for photodynamic therapy; light, a photodynamic molecule or metal compound as the mediator, and the oxygen in the micro-environment. The product of this reaction, a reactive singlet oxygen species compound, kills the cancer.
Spectroscopy plays an important role in identifying the most productive photodynamic molecules that can be used to activate the process.
In photodynamic therapy, a cancer patient has a fiber optic light either inserted into, or placed just outside their body. This light emits visible wavelengths. It reacts with photosensitizer (photodynamic) molecules and provides energy to oxygen in the microenvironment. That, in turn, generates non-toxic singlet oxygen species which shrink or kill the tumor.
Singlet oxygen species are reactive chemical varieties containing oxygen. The singlet oxygen species attack and destroy the cancerous cells, leaving surrounding healthy cells intact.
Unlike conventional radiation treatment, photodynamic therapy uses neither toxic radicals nor a toxic light source to destroy the cancerous cells. The materials used are benign and non-toxic, and leave healthy cells unaffected by the treatment. The patient is also spared undesirable side effects.
Researchers must identify the most effective photodynamic molecules that produce the cancer-killing singlet oxygen species. To do this, spectroscopy is used to measure the reaction of the minerals to the light source. Those mineral compounds that produce the most successful singlet oxygen species are identified through spectroscopy and further refined.
University of Nevada Reno researcher Ana de Bettencourt-Dias, Ph.D., leads a group looking into a category of minerals called lanthanides. The group uses fluorescence spectroscopy to determine the properties of the light-emitting compounds, which, with the exposure to light sources, generate reactive oxygen species. Their goal is to find the best lanthanide-based compounds for creating these reactive oxygen species.
The Reno research group studies the light emission of the molecules it makes, using a HORIBA Instrument’s Fluorolog®-3, a steady state and lifetime modular spectrofluorometer. They use the Fluorolog to measure the efficiency of the light emission of the compounds and therefore the most efficient compounds for light emission, and compare different compounds to each other.
De Bettencourt-Dias is interested in developing new ligands, which are ions or molecules attached to a metal atom, for highly radiating lanthanide ion complexes. The team synthesizes the ligands and the metal complexes. They then characterize these with different spectroscopic methods, such as single crystal X-ray diffraction, and absorption, excitation and emission spectroscopy.
Photodynamic therapy has been used to treat colon cancer, ovarian cancer, cervical cancer, and skin cancer. Sometimes it will shrink a tumor in order to allow it to be surgically removed.
There is a shallow penetration of the visible light, University of Massachusetts-Medical School Researcher Gang Han, Ph.D. said. That’s the limitation of photodynamic therapy for clinical practice. Han wants to create a new version of a photodynamic therapy photosensitizer that has amplified near-infrared absorptions, with a much better tissue-penetrating light. In this way, practitioners can go deeper into the tissue to treat cancer, such as in the lung, breast or liver.
Research continues to seek better compounds to use as photosensitizers, using spectroscopy as a principal research tool.
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