Near-infrared Fluorescent Probe For Hypochlorous Acid: Design,Synthesis And Bioimaging Applications

Hypochlorous acid(HOCl)is one of the important reactive oxygen species,which is relevant to many physiological and pathological processes.Monitoring its concentration in situ is great significance.Fluorescent probes possess many superior characteristics such as simplicity,noninvasiveness and visualization,which have been widely used in basic medical research and disease diagnosis.Especially,near-infrared(650-900 nm)probes show obvious advantages in bioassay for their low tissue absorption and scattering,low autofluorescence and deep penetration.These probes can be categorized into“turn-on”fluorescent probe and ratiometric flurescent probe.NIR probes play important role in HOCl bioassay,but there are still some disadvantages.The former ones always show a small Stokes shift and the latter ones suffer from a short emission shift.Based on the modification of rhodamine and biscyano-isophorone dyes,the“turn-on”NIR probe with a large Stokes shift and the ratiometric NIR probe with a large emission shift was fabricated.(1)Through introducing a rigid heterocycle into one side of rhodamine dye,a NIR fluorophore with a large Stokes shift was obtained for the extended?-conjugated system and asymmetry.What's more,a hydrophilic PEG chain and positively charged pyridine salt were introduced to improve its water-solubility and confer mitochondrion-localization ability.The obtained NIR fluorescent probe TJM shows an emission peak at 730 nm,with a large Stokes shift of 145 nm.This probe shows obvious fluorescence enhancement in presence of HOCl and can be applied in HOCl imaging in living cells,zebrafish and tumor mice.(2)Biscyano-isophorone dye was chosen as the NIR fluorophore due to its simple synthetic procedure.Thiocarbamate was employed as the recognition group of HOCl and Cl~-was introduced to modulate the emission shift after reaction with HOCl.CN-MTC and CX-MTC were synthesized and their photophysical properties were studied.It was found that CX-MTC shows a larger emission shift of 140 nm after reaction with HOCl.Besides,it also possesses high fluorescence quantum yield.CX-MTC was suitable for detecting endogenous HOCl in living cells,zebrafish and mice.It can also be successfully used in monitoring the dynamic change of HOCl in the wound healing process of diabetic model mice.