Hypochlorous acid (HClO) is generated from hydrogen peroxide and chloridion via the catalysis of myeloperoxidase (MPO) in vivo. Normally, HClO acts as omnipresent intracellular regulator within life cycle of the cell, activating signaling pathways for cell differentiation, migration, transmission, proliferation and immune in physiological and pathological processes. Therefore, it is of vital importance to the detection and recognition of hypochlorous acid. Owing to simple operation, high sensitivity, sensitivity, low detection limit, rapid response, excellent spatial and temporal (spatiotemporal) resolution and especially nondestructive characteristics, Fluorescent probe technique has been paid special attention to research the physiological function of hypochlorous acid in vivo. Based on the recognition mechanism of fluorescent probes with hypochlorous acid, this review mainly summarizes the research progress of fluorescent probe for the recognition of hypochlorous acid in last three years. The design strategy of molecular structures and response pattern of these probes are also discussed as well as biological application. The development direction and biological application of hypochlorous acid fluorescent probes are also prospected.

Contents
1 Introduction
2 Types of fluorescent probes for HClO
2.1 Oxidation deoximation reaction
2.2 Oxidation unsaturated double bond reaction
2.3 Oxidation p-methoxy phenol reaction
2.4 Oxidation anisidine reaction
2.5 Oxidation chalcogenide (S, Se and Te) reaction
2.6 Oxidative dehydrogenation reaction
2.7 Oxidation hydrazide reaction
2.8 Oxidation metal ion reaction
2.9 Other types of oxidation reaction
3 Conclusion and outlook