A colorimetric and ratiometric fluorescent probe of hypochlorous acid and its bio-imaging application

A new ratiometric and colorimetric fluorescent probe HTD was synthesized based on the reaction of 4-aminophenyl boronic acid pinacol ester and 4-(3-formyl-4-hydroxyphenyl) benzonitrile. The probe exhibited a unique fluorescence response to hypochlorous acid and had good anti-interference performance in the presence of other interference. When HTD met the NaClO, the light orange fluorescence was changed to green with the blue-shifted emission wavelength from 550 to 500 nm. Moreover, the absorbance of HTD's UV-vis at 300 nm and 375 nm decreased in the presence of NaClO. The limit of detection was 1.83 × 10^-7 M and 2.96 × 10^-6 M based on the fluorescence and UV-vis titration data. NMR, HRMS, and IR spectra suggested that the possible sensing mechanism of HTD to NaClO was the formation of initial compound 4-(3-formyl-4-hydroxyphenyl) benzonitrile due to the oxidation of hypochlorous acid in aqueous solution. The portable test strips were obtained, and the real water sample test reached good results with spiking recoveries among 92.00% ~ 103.25%. Finally, endogenous hypochlorous acid produced by LPS and PMA was successfully detected by HTD in living mice using in situ fluorescence bioimaging.