Nanosensor quantitative monitoring of ROS/RNS homeostasis in single phagolysosomes of macrophages during bactericidal processes

Reactive oxygen and nitrogen species (ROS/RNS) in macrophages have a potent killing effect on pathogens that infect the host. Here, we achieved <i>in situ</i>, quantitative detection of the homeostasis of four primary ROS/RNS (ONOO^-, H₂O₂, NO, and NO₂^-) and their precursors (O₂˙^-, NO) in phagolysosomes of single RAW 264.7 macrophages after phagocytosis of <i>Escherichia coli</i> with platinum-black nanoelectrodes. Enhanced bactericidal activity of the macrophages was observed by an increase in the total amount of ROS/RNS as well as the level and proportion of ONOO^-, a potent bactericidal species of RNS. Moreover, both the bactericidal process and the steady-state replenishment process were dominated by the production of RNS (NO-based), revealing differences in the enzyme kinetics of the bactericidal process.