Figure 1.

General schematic representation of Photodynamic Therapy (PDT): A. Illustration of PDT where photosensitizer (PS) serves as both an imaging agent and a therapeutic agent. Advantages, disadvantages, and different strategies to enhance PDT of cancer. B. Modified Jablonski diagram showing the principle of PDT: Absorption of light energy by ground state PS (S₀) results into its excitation to singlet ¹PS^* (S₁). Intersystem crossing (ISC) transforms the S₁ to excited triplet ³PS^* (T₁). T₁ either through electron transfer to cellular biomolecules (Type I) and/or via direct energy transfer to ³O₂ (Type II) results in the production of Reactive Oxygen Species (ROS) to induce cell death.