Probing the Catalytic Effects of Gold Nanoparticle Surfaces for a Proposed Cancer Tumor Radiosensitization Mechanism

Radiotherapy is used to treat malignant neoplasms. Ionizing sources range from photons (gamma rays or x-rays) to particles (alpha particles, protons, or neutrons). A significant challenge with conventional cancer treatments is the collateral damage to surrounding healthy tissue. Therefore, the goal of optimizing therapies is minimizing the dose received while maximizing tumor shrinkage. This is accomplished with radiosensitizers. Chemicals have been used as sensitizers for years; however, gold nanoparticles have recently shown promise as alternatives. In both in vivo and in vitro studies, the radiosensitization effects of gold nanoparticles have been shown to mainly be independent of the ionizing radiation source, resulting in effective radiosensitization at most doses. However, multiple mechanisms behind radiosensitization have been proposed. One explanation involves surface catalysis, where the nanoparticle surface enables the cycling of reactive oxygen species (ROS). In this model, nanoparticles act as enzyme mimetics, serving as electron relays in redox reactions between an electron donor (typically an antioxidant biomolecule) and an electron acceptor (usually an oxygen-containing species). This mechanism depends on the nanoparticle's surface properties and availability of catalytic centers. My research focuses on ascorbic acid (vitamin C) as a model antioxidant, investigating how the kinetics of this catalytic process vary with nanoparticle size, shape, and surface coating. Surface characterization was performed using UV-Vis to monitor the catalyzed O2-driven oxidation of ascorbic acid. This work aims to deepen our understanding of the mechanisms underlying the radiosensitization of gold nanoparticles.