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Porphyrin dimers for photodynamic therapy via two photon absorption

Final Activity Report Summary - PORPHYRIN DIMER PDT (Porphyrin Dimers for Photodynamic Therapy via Two Photon Absorption)

We designed and successfully synthesised a series of water soluble conjugated porphyrin dimers. We fully explored their photophysical and biological properties and showed that all synthesised dimers had very high two-photon absorption cross-sections, i.e. very high ability to absorb two photons simultaneously, and singlet oxygen yields, properties crucial for practical applications of two-photon photodynamic therapy.

Porphyrin dimers are a new class of compounds that become toxic only when struck by two photons simultaneously. This means that very few cells outside of the most intense part of the laser focus are affected. Importantly, low-energy near-infrared light can be used, which can penetrate two or three times deeper into living tissue than the currently common laser. This property should allow for broader application for photodynamic therapy (PDT) in medicine. Using these conjugated porphyrin dimers we were able to demonstrate, for the first time, blood vessel closure in a live mammal by highly selective two-photon excited PDT. Our research outlined a novel method which increased the selectivity of photodynamic therapy and minimised collateral damage. The most immediate application was the treatment of the wet form of age-related macular degeneration (AMD) by closing off unwanted blood capillaries. Other possible applications emerged particularly in neurosurgery, where precise minimally-invasive treatment is of key importance. Our research article describing the above results was highlighted in Nature, entitled ‘Cancer zapper’, as well as in Chemistry World, entitled ‘Improving photodynamic cancer therapy’.