ABSTRACT
The use of light-absorbing chemicals to cause photoreactions in biological systems dates back to at least 1900 when Raab (1) reported a lethal effect on paramecia exposed to light and an acridine dye. Since that time, numerous examples of the photodynamic effect have been reported for a wide range of photosensitizers both in vitro and in vivo (2). Oxygen is usually required in addition to a photosensitizer and light. The mechanism generally accepted for inactivation of biological systems is an energy-transfer process from the excited triplet state of the sensitizer to oxygen, producing singlet oxygen, which causes irreversible oxidation of some essential cellular component.
