Jonghoon Oh, and Hyoung-Ryun Park

nal standard Photodynamic therapy (PDT) has been used for diagnosis and treatment of patients with various malignant tumors, including cancers of the skin, gastrointestinal tract, lung and uterus. 1 Recently, PDT with using 5-aminolevulinic acid (ALA) for cutaneous diseases has been attracted consider-able attentions, because skin is easily accessible to light and drugs. Since ALA was used as a pre-drug of the photo-sensitizer in PDT research by Kenedy et al. in 1990, 2 a number of ALA ester derivatives have been synthesized and applied to PDT. ALA and its ester derivatives are precursors of protoporphyrin IX (PpIX) in the biosynthetic pathway of heme. 3,4 They are normally biosynthesized in vivo from glycine and succinyl-coenzyme A in mitochondria and then converted into the actual photosensitizer, PpIX. 5 PpIX produced through the heme biosynthetic pathway emits fluorescence strongly and photobleaches rapidly under production of singlet oxygen. 6 The amount of ALA-induced porphyrins can be generally determined by measuring the fluorescence under various experimental conditions. Most papers have reported that the amount of fluorescence was determined by the measurement of fluorescence intensity at the maximum emission wavelength