Abstract

Use of porphyrin photosensitizers in photodynamic therapy (PDT) is gaining acceptance worldwide as an alternative treatment of tumors¹ and age-related macular degeneration.² Utility of porphyrins is based on their special ability to accumulate in pathologic cells, and to transfer absorbed photon energy efficiently to extremely active singlet oxygen molecules, which then wipe out the surrounding tumor. So far, the limited penetration depth by visible light into biological tissue has allowed only few types of skin, breast and certain endoscopically accessible cancers to be treated in this fashion. It has been proposed that by utilizing two-photon absorption (TPA), in which case illumination is carried out at near- 1R wavelengths, the PDT may be delivered deeper into the tissue. However, tetrapyrrolic photosensitizers studied so far display disappointingly small TPA cross-sections, typically on the order of,_Tσ _PA = 1-10 GM (1GM=1•10⁻⁵⁰ cm⁴-s/photon).³

© 2002 Optical Society of America