New Tech for Photodynamic Therapy

Essay by iLoveScienceHigh School, 12th gradeA, June 2014

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New Tech for Photodynamic Therapy

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Photodynamic therapy (PDT) is an effective treatment for easily accessible tumors such as oral and skin cancer. The cancer cells absorb special drugs, called photosensitizing agents, which are delivered to the tumor via the bloodstream or locally. Visible light is then applied to the site, which causes the drug to react with oxygen and create a burst of free radicals that kill the tumor. Unfortunately, visible light does not penetrate tissue well.

To solve this problem, some researchers are developing drugs that absorb near-infrared light. However, it is difficult to synthesize near-infrared absorbing photosensitizers that are stable and efficient (. The University of Boston-led team took a different approach, which uses the tumor's natural environment to tune the light into a wavelength necessary to activate the drug.

For example, the near-infrared laser beam interacts with the natural protein collagen, which is found in connective tissues.

The interaction changes the near-infrared light to visible light, a process known as second harmonic generation. Second harmonic generation is a process in which photons of the same frequency are combined to generate new photons with twice the energy (Franken, Hill, Peters, & Weinreich, 1961). Likewise, natural proteins and lipids within the cells interact with near-infrared laser light and change it to visible light through another process called four-wave mixing. Four-wave mixing is where the interactions between two wavelengths produce two more wavelengths in the signal (Thiel, n.d.).

Thus, visible light can be generated in tumors deep inside the body using the body's own structures, and it can be absorbed by the drug. This activates the drug, which then destroys the tumor.

With this new breakthrough, PDT provides doctors another tool that can help alleviate the pain of people suffering from cancer.