Recent developments of small-molecule fluorescent probes for the detection of hydroxyl radical in biological systems

Intracellular reactive oxygen species are mainly produced from oxygen through electron-transfer reactions, which diffusely discovered in biological organisms. Among them, hydroxyl radical (•OH) embodies crucial physiological functions and roles. However, the over-whelming of •OH are associated with various oxidative stress-related pathophysiological disorders, such as inflammation, liver injury, depression, and cancer. Nevertheless, some exact pathogenic traits of •OH in biological systems remain unknown because of its high reactivity, short half-life, and low concentrations. To better grasp the characteristics of •OH in physiological and pathological processes, it is crucial to develop highly sensitive and selective detection tools. Thus, small-molecule fluorescent probes have proven to be useful tools for in situ and real-time monitoring of variations in reactive species in living systems, owing to their high spatiotemporal resolution, noninvasiveness, high sensitivity, and high selectivity. In this regard, this review discusses high-performance molecular probes for monitoring •OH fluctuations and studying the relevant mechanisms in living systems. We expect that this review will provide a comprehensive introduction to •OH-responsive fluorescent probes and their further applications in biomedical and clinical fields.