Construction and Application of Fluorescent Probes with Imine Protective Groups for Hypochlorite Detection

Several fluorescent probes have been designed to detect ClO^- in biological systems based on the isomerization mechanism of C = N bonds. Particularly, fluorescein has emerged as an important fluorophore for detecting ClO^- because of its unique properties. Previously, we introduced the fluorescein analog F-1 with an active aldehyde group. In this study, two ClO^- fluorescent sensors (F-2 and F-3) with imine groups were designed and synthesized using diaminomaleonitrile and 2-hydrazylbenzothiazole as amines. The electron cloud distribution of F-2 and F-3 in ground and excited states was explored via Gaussian calculations, reasonably explaining their photophysical properties. The fluorescence detection of ClO^- in solution using the two probes (F-2 and F-3) was realized based on the mechanism of imine deprotection with ClO^-. NaClO concentration titration demonstrated that the colorimetric detection of ClO^- with the naked eye could be achieved using both F-2 and F-3. However, after adding ClO^-, the fluorescence intensity of probe F-2 increased, whereas that of probe F-3 first decreased and then increased. Probes F-2 and F-3 exhibited good selectivity, anti-interference capability, and sensitivity, with the detection limits of 169.95 and 37.30 µM, respectively. Owing to their low cell toxicity, probes F-2 and F-3 can be applied to detect ClO^- in vivo. The design approach adopted in this study will further advance the future development of ClO^- chemical probes through the removal of C = N bond isomerization.