THE MECHANISM OF PHOTOSENSITIZATION IN PHOTODYNAMIC THERAPY: CHEMILUMINESCENCE CAUSED BY PHOTOSENSITIZATION OF PORPHYRINS IN SALINE CONTAINING HUMAN SERUM ALBUMIN

Abstract— Chemiluminescence (CL) caused by photosensitization of porphyrins in phosphate buffered saline (PBS) solution containing 3% human serum albumin (HSA) was observed for the first time. Irrespective of porphyrins concerned, CL shows a spectrum ranging from 380 to 520 nm with a peak near 450 nm and decays almost single‐exponentially with a lifetime of about 15 s. The intensity of CL depends on concentrations of porphyrins and HSA in PBS solution. We have examined a number of porphyrins and observed CL for the compounds with triplet lifetimes longer than 0.1 ms. The appearance and quenching of CL by photosensitization of porphyrin‐HSA systems indicate that type II reaction by singlet oxygen occurs significantly in photodynamic therapy resulting in hypoxic regions in environments surrounding the sensitizer.

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