Application of nanomaterials in photodynamic therapy

Photodynamic therapy is a noninvasive method for the treatment of cancer malaise. It involves generation of reactive oxygen species which interact with the cancer cells to a transformational point of cell death by apoptosis or necrosis (Van Driel et al. 2016). The reactive oxygen species are generated via interaction of a nontoxic light (red or near-infrared) of a suitable wavelength with a photosensitizer and molecular oxygen. The interaction of light with photosensitizer often leads to photochemical generation of excited triplet state which interacts with molecular oxygen causing outbursts of reactive oxygen species via type I and type II reactions (Chiaviello et al. 2011). The type I reactive oxygen species, namely superoxide anion (O₂ ⁻), hydrogen peroxide (H₂O₂), and hydroxyl radical (·OH) are generated through transfer of electron to molecular oxygen and abstraction of hydrogen from nearby biomolecules while the most prominent reactive oxygen species, singlet oxygen (¹O₂), is generated via direct transfer of photon energy to molecular oxygen (Chiaviello 2011; Ormond and Freeman 2013; Scheme 13.1).