Photodynamic therapy with topical aminolevulinic acid

Figure 2 Cellular damage mechanism. Type-I and Type-II photoreactions, where ¹P is a photosensitizer in a singlet ground state, ³P¹ is a photosensitizer in a triplet excited state, S is a substrate molecule, P^ÿ is reduced photosensitizer molecule, S is an oxidized substrate molecule, O₂ is molecular oxygen (triplet ground state), O^ÿ₂ is the superoxide anion, O₂ is the superoxide radical, P is the oxidized photosensitizer, ³O₂ is triplet ground-state oxygen, ¹O₂ is oxygen in a singlet excited state, and S (O) is an oxygen adduct of a substrate (adapted from Macdonald et al[1]).