Functionalized Quartz Nanopipette for Intracellular Superoxide Sensing: A Tool for Monitoring Reactive Oxygen Species Levels in Single Living Cell

Reactive oxygen species (ROS), including superoxide radical anions, are vital components in numerous biological functions, including cell signaling and immune responses. Since ROS react with other biomolecules and oxidize them quickly, it is essential for cells to have superoxide-scavenging enzymes and other regulating enzymes that can catalyze the dismutation of superoxide radical anions into less damaging molecules. Otherwise, ROS overproduction can cause oxidative damage to DNA, proteins, cells, and tissues, damage that is associated with the pathogenesis of a range of neurodegenerative disorders, age-related diseases, and cancer. Understanding the relationship between superoxide and these disorders can help the development of innovative therapies for combating oxidative stress and degeneration of nerve cells. Although methods to quantify ROS already exist, they are indirect, destructive, ambiguous, and/or cannot provide real-time measurements in single cells. In this paper, we report a technique for sensing superoxide radical anions in single living cells using functionalized nanopipettes. These nanopipettes allow us to enter the cell as we measure intracellular ROS concentrations over time. We observed that these devices provide precise real-time measurements that are accurate and not possible to obtain with other conventional techniques.