Recent progress in small-molecule fluorescent probes for the detection of superoxide anion, nitric oxide, and peroxynitrite anion in biological systems.

Superoxide anion (O˙), nitric oxide (NO), and peroxynitrite anion (ONOO) play essential roles in physiological and pathological processes, which are related to various symptoms and diseases. There is a growing need to develop reliable techniques for effectively monitoring the changes in these three reactive species across different molecular events. Currently, small-molecule fluorescent probes have been demonstrated to be reliable imaging tools for the optical detection and biological analysis of reactive species in biological systems due to their high spatiotemporal resolution and capabilities. In consideration of the distinct features of these three reactive species, abundant fluorescent probes have been developed to meet various requirements. In this context, we systematically summarized the latest progress (2020-2023) in organic fluorescent probes for monitoring O˙, NO, and ONOO in living systems. Furthermore, the working principles and biological applications of representative fluorescent probes were illustrated. Moreover, we highlighted the current challenges and future trends of fluorescent probes, offering general insights into future research.