Fig. 1.

Mechanisms of PDT. PDT encompasses two main reactions: Type I and Type II. In Type I reactions, the photosensitizer interacts with nearby molecules, forming radical anions or cations, which then react with molecular oxygen to produce ROS like superoxide anions and hydroxyl radicals. These ROS cause oxidative damage to cellular components, including lipids, proteins, and DNA, leading to cellular dysfunction and death. Type II reactions involve the transfer of energy from the excited photosensitizer to ground-state molecular oxygen, producing singlet oxygen, a highly reactive form of oxygen that directly oxidizes biological molecules, causing similar oxidative stress and damage. The combined effects of these reactions create an environment of oxidative stress, overwhelming the cell’s antioxidant defenses, disrupting cellular homeostasis, and triggering cell death pathways such as apoptosis, necrosis, and autophagy. This dual mechanism makes PDT an effective treatment for targeting and destroying cancer cells. ground-state