Small molecule fluorescent probes for the detection of reactive nitrogen species in biological systems

Reactive nitrogen species (RNS) as a class of vital reactive molecules, are essential for maintaining homeostasis. Among RNS, nitric oxide (NO or NO.), peroxynitrite anion (ONOO–) and nitroxyl (HNO) play crucial roles in several physiological, pathological and pharmacological processes. However, abnormal variations of these RNS concentrations are closely intertwined with the occurrence and progression of numerous diseases. Hence, the intuitive and accurate visualization of RNS is extremely significant for deeper insight into their spatial distribution, physiological and pathological roles, functions, internal interactions and potential mechanisms in biological systems. To date, the fluorescence imaging technique has been demonstrated to a powerful strategy for the rapid and precise detection of reactive species in biological systems. Moreover, small molecule fluorescent probes have been successively fabricated for in suit, real-time, sensitively and selectively monitoring the changes of RNS in living systems. Based on the inherent characteristics of three RNS, abundant fluorescent probes have been elaborately constructed to satisfy various requirements. Therefore, in this review, we briefly summarize the recent advances in small molecule fluorescent probes for monitoring of NO, ONOO– and HNO within 8 years. Moreover, the classifications, design strategies, recognition mechanisms and biological applications of three RNS-responsive fluorescence probes are discussed in depth. Particularly, the challenges and further development directions in this hot field of fluorescent imaging are definitely emphasized.