Designing Fluorescent Probe For Detecting Hydrogen Peroxide Based On Excited State Intramolecular Proton Transfer Mechanism

Hydrogen peroxide?H₂O₂?,as the second messenger molecule in intracellular signal transduction and a crucial component in maintaining intracellular redox homeostasis,is closely related to the occurrence and development of various diseases.Therefore,the detection of intracellular H₂O₂ is very important to clarify its role in physiological and pathological processes.Fluorescence imaging technology has become a widely concerned method for monitoring biomolecules due to its simple operation,high sensitivity and non-invasive characteristics.Excited state intramolecular proton transfer?ESIPT?is an attractive fluorescence generation mechanism.The fluorescent reporter molecules based on ESIPT mechanism have the advantages of large Stokes shift?²00 nm?,high environmental sensitivity and easy modification.In this paper,we developed H₂O₂-responsive fluorescent probes based on the mechanism of ESIPT.The main contents are summarized as follows:?1?Using 2-?2'-hydroxy-5'-methylphenyl?benzothiazole as fluorescent skeleton,we designed the ESIPT-based fluorophore BTFM-OH,which possesses the longer emission wavelength based on introduction of an aldehyde group on the phenyl ring.A fluorescent probe BTFMB was further constructed to detect H₂O₂ by masking the hydroxyl group of BTFM-OH with pinacol phenylborate ester.The probe has the following characteristics:a)easy preparation through cheap and readily available raw materials;b)large Stokes shift?162 nm?;c)low detection limit?109 nM?.In addition,the probe was successfully applied for monitoring the change of H₂O₂ levels in the induction and inhibition of ferroptosis.?2?Furthermore,we introduced the strong electron-withdrawing dicyanoisophorone into the classical ESIPT fluorophore 2-?2'-hydroxy-3'-methoxyphenyl?benzothiazole?HMBT?to acquire the near-infrared fluorophore HMBTDM.On the ground,a novel near-infrared fluorescence probe HMBTDM-H₂O₂ for monitoring H₂O₂ was constructed with the phenylborate ester as a responsive site.The probe has the characteristics of high selectivity,low detection limit?81.6 nm?,large Stokes shift?330 nm?and long emission wavelength?730 nm?.The probe was also applied for monitoring the change of H₂O₂ levels during the development of Parkinson's disease,and identifying the pro-oxidative anti-cancer activity of dietary[6]-shogaol and its analogs.The anti-cancer theranostic prodrugs have dual functions of cancer diagnosis and treatment.Under the cancer-specific conditions,prodrug molecules can be activated to release the fluorescent sensor molecules and chemotherapeutic agents for achieving the purpose of specific cancer therapy and high-precision cancer imaging.Compared with normal cells,cancer cells harbor relatively higher levels of glutathione?GSH?.Therefore,based on the difference of GSH levels between normal cells and cancer cells,the development of anticancer theranostic prodrugs has become a research hotspot.In another part of this paper,we designed and synthesized a GSH-activated theranostic prodrug.?3?Given that cancer cells contain higher concentration of GSH than normal cells,we utilized HMBT as a fluorescence reporter,7-ethyl-10-hydroxycamptothecin?SN-38?as a drug molecule,and 2,4-dinitrobenzenesulfonates?DNBS?as a GSH-responsive group to construct the prodrug molecule BCMD-SN-38.We reasoned that upon GSH-mediated conversion of DNBS to phenol,the prodrug can release SN-38 and HMBT via 1,6-elimination.At present,we have completed the synthesis of the prodrug,and expected that it holds promise for achieving cancer accurate targeting,diagnosis and treatment based on the in situ release of SN-38 and HMBT by increased levels of GSH.