Singlet oxygen - is it useful for PDT?

Oxygen is the limited component in PDT, especially in the hypoxic tissues. Proteins and amino acids are the main oxidation substrates in tissues in the case of singlet oxygen while, for example, hydroxy radicals well oxidize also DNA and membrane lipids which are considered as the critical targets in PDT. We compared the quantum yields of the oxygen consumption by Type I and by Type II mechanisms in the aqueous solutions in the comparable with PDT conditions. The preparation Photosens was used as photosensitizer, human albumin serum - as oxidation substrate, and sodium ascorbate - as reductant. We conclude that the oxygen consumption proceeds mainly by Type Il mechanism while PDT efficiency by Type I mechanism can be even higher.