Fluorescence response of a fluorescein derivative for hypochlorite ion and its application for biological imaging in wounded zebrafish and living mice

Hypochlorite ion (ClO−) is a significant reactive oxygen species in physiological and pathological processes. However, excess ClO− may be disruptive and result in many diseases. To visualize and monitor ClO− in living subjections, two fluorescein derivatives with 8-hydroxyjulolidine (FCJD)/4-morphalinabenzene (FCMB) as terminal groups were developed. While FCMB shows fluorescence turn off response to ClO−, the structurally similar FCJD exhibits fluorescence turn-on response for hypochlorite ion with low detection limit (57.8 nM), quick responding (20 s) and is successful for monitoring endogenous hypochlorite ion in RAW 264.7 cells and zebrafish and exogenous hypochlorite ion in living mice. Furthermore, FCJD is able to demonstrate the generation of ClO− as an emergency response of zebrafish being wounded. The recognition mechanism analysis indicates that FCJD is firstly oxidized to diimide intermediate under the support of the adjacent hydroxyl in julolidine moiety and then followed by a hydrolysis process to restore fluorescein with strong green fluorescence.