Reactive oxygen species (ROS) are often viewed as highly unstable, degradable and transient molecules, associated only with pathological processes. However, recent studies demonstrate that one particular ROS, hydrogen peroxide (H2O2), fits the requirements of a signalling molecule, including controlled production and destruction, biological stability, and specificity in targets. The concentration, location and context in which H2O2 is produced in a cell determine whether it functions as a stress or signalling molecule. In order to elucidate the disparate roles of H2O2 and its involvement in physiological and pathological conditions, it is critical to be able to detect this specific ROS in the context of other chemically similar ROS with spatio-temporal resolution in complex living systems. In order to achieve this, a variety of new tools have been developed to detect H2O2 in living cells and animals. This review focuses on two of the most promising classes of H2O2 reporters: small molecule boronate fluorescent probes and genetically encoded fluorescent protein reporters. The advantages and limitations of each of these systems will be discussed with a focus on real-time imaging. As our understanding of the biology of H2O2 continues to expand, it becomes increasingly important to visualise this specific ROS in order to fully appreciate its contributions to both physiological and pathophysiological conditions.
Keywords: Boronate, hydrogen peroxide, HyPer, microscopy, orp1-roGFP2, spatio-temporal, Redox signalling, NADPH oxidase (NOX) proteins, Adult hippocampal progenitor, Caenorhabditis elegans, Dihydrodichlorofluorescein, Dihydrorhodamine 123, Dual oxidase, Electron transport chain, Fibroblast growth factor