Antioxidant studies are important for understanding oxidative stress and developing preservative techniques for food and medicine. There has been increasing interest in the study of natural antioxidants, such as vitamins, due to their biocompatibility, relatively low cost, and high antioxidant capacity. Spectroscopic tools, including fluorescence and electron spin resonance, have been developed to evaluate the antioxidant capacity. However, it is difficult for these methods to measure the antioxidant capacity against specific reactive oxygen species (ROS). Based on a recently developed