It is generally established that the intracellular reactive nitrogen species (RNS) which contain nitrogen atoms are one class of highly chemical active species. These species have attracted increasing attention and become an active research field based on their key roles in special functions during a series of physiological and pathological processes. In order to elucidate these roles of RNS, the design and development technology for selective and sensitive detection to RNS in vivo are crucial. Advanced with high sensitivity, good selectivity, noninvasive detection and real-time visualization in situ, fluorescent probes provide facilitative and effective chemical approaches in modern biochemistry analysis. Progress in the field of fluorescent probes for RNS promises to advance our knowledge of essential cellular signal transduction during the varieties of physiological and pathological processes, which is indicated in human health and disease. According to the current situation, we review the past four years'latest five types of RNS probes for nitric oxide (NO), peroxynitrite (ONOO^-), nitroxyl (HNO), nitrite (NO₂^-) and nitrogen dioxide (NO₂). In this article, the design strategies, fluorescent response mechanisms and biological applications of the probes are discussed. Finally, the prospect to design and applications of probes is given.

Contents
1 Introduction
2 Fluorescent probes for NO
2.1 NO-induced o-phenylenediamine cyclization reaction
2.2 NO-induced spirocyclic opening reaction
2.3 NO-induced diazotization
2.4 Reaction between transition metal and NO
2.5 NO-induced denitrogenation reaction
3 Fluorescent probes for ONOO^-
3.1 ONOO^- probe based on mimicked selenoenzyme
3.2 ONOO^- probe based on oxidized-borate reaction
3.3 ONOO^- probe based on oxidative coupling reaction
3.4 ONOO^- probes based on like-Baeyer-Villiger reaction
3.5 ONOO^- probes based on other chemical reaction
4 Fluorescent probes for HNO
4.1 Fluorescent probe based on the reaction between Cu(Ⅱ) and HNO
4.2 HNO probes based on other chemical reaction
5 Fluorescent probes for NO₂^-
6 Fluorescent probes for NO₂
7 Conclusion and outlook