Design And Biosensing Application Of Fluorescent Probes Based On Benzoxazole,?-carboline And Naphthalene Anhydride

Possessing the advantages of simple operation,low detection limit,real-time detection and live imaging,fluorescent analysis method has been widely used in detection of small biological molecules and biological imaging.In order to get a better understanding of biological functions and elaborate the production,transportation and downstream functions of small biological molecules,the organic fluorescent probes have been gradually developed into important tools for testing bioactive molecules and researching on their physiological and biochemical process.Centreing on fluorescence detection study on biological thiols,ascorbic acid and metal ions,a series of fluorescent probes based on reaction types and coordination types were designed,synthesized and fully characterized.Moreover,we further studied the recognition mechanisms and biosensor applications of them.1.A simple fluorescent sensor?AHBO?based on ESIPT mechanism was designed and synthesized by using benzoxazole as the fluorophore and azide group as the recognition unit.In HEPES test system containing 50%CH₃CN?10 mM,pH 7.4?,the absorption intensity of AHBO at 344 nm decreased upon addition of 2 eq GSH and Cys,while the fluorescence intensity at 488 nm gradually increased,achieving the maximum after 5 min.The detection limit could reach to 90 nM.The solution color of fluorescent probe changed from colorless to cyan,which was observed with a 365-nm portable UV lamp.Through nucleophilic substitution-rearrangement reactions,the probe?AHBO?with good selectivity and high sensitivity had been successfully applied in quantitative detection of GSH in human serum and fluorescence imaging of endogenous GSH in cancer cells,showing the potential application value.2.In this work,modifying azide group at 6-C of?-carboline alkaloid,we reported herein the design and synthesis of the turn-on probe KL-DN for selective detection of Cys and GSH.Upon addition of 2 eq GSH,the absorption intensity of the probe at 310 nm increased,and the fluorescence intensity at 487 nm reached to the maximum in 2 min with the detection limit of92 nM which is far below the level of GSH physiological environment.The detection mechanism and product were verified by analysis of nuclear magnetic titration,high performance liquid chromatography and liquid mass.Via redox reaction,GSH could be quickly recognized by azide.The probe,which has low toxicity,good membrane permeability and excellent water solubility?comparing with AHBO?,was for the first time applied to the detection and fluorescence imaging of endogenous GSH in cancer cells and wheat germ tissues.3.Ascorbic acid?AA?is a vital nutritional factor in many fruits and plants,and abnormal levels of AA are closely associated with several diseases.Therefore,the development of convenient methods for monitoring AA levels in biological systems is of great importance.In this work,we designed and synthesized three chemosensors which were based on a1,8-naphthalimide moiety with the azide group at different sites?Probes 1,2,and 3?.The fluorescence intensity of Probe 2 reached to the maximum within 1 min upon addition of 2 eq AA through the redox reaction.Meanwhile,Probe 2 showed high selectivity toward AA,having an experimental limit of detection of 74 nM.Although Probe 1 could be reduced by AA,the fluorescence intensity of AA had no change due to PET process.The reduction product of Probe 2 with AA was verified by ¹H NMR,¹³C NMR and mass spectram.Its reduction was easier than that of Probe 3 with a 3-substituted azide group.Moreover,Probe 2was successfully used for imaging of AA in garlic slice tissues for the first time.4.According to molecular hybridization principle,we designed and synthesized two series of hybrid molecules and preliminary discussed on their physical properties.Through click reaction,carbazole,?-carboline and 1,8-naphthalene anhydride fluorophore were linked by triazole ring.The results showed that when the proportion of water phase gradually increased,hybrid molecules began to aggregate and the fluorescence signal of them gradually increased.The optical properties,crystal structure analysis and scanning electron microscopy indicated that hybrid molecules aggregated via?-?accumulation resulting in AIE property.When added metal ions(Al³⁺)in DMSO solution containing 50%water,the hybrid molecules containing?-carboline unit could coordinate with metal ions leading to repelling of positive charges and depolymerization in DMSO solution containing 50%water.Meanwhile,compound 5-9 could be used as a new ratio fluorescent probe for Al³⁺with dual-channel fluorescence signal and was successfully applied to fluorescence detection analysis of Al³⁺in sanitary sewage samples.Starting with different azide-modified fluorophore molecular structures,fluorescent probes based on benzoxazole,?-carboline alkaloid and 1,8-naphthalimide were designed and synthesized.They were further applied to high sensitive and selective detection of biological thiols,ascorbic acid and Al³⁺,which are closely related to biological life activities.This work provides new research ideas and experimental basis for azide-modified small molecular fluorescent probes with the detection of thiols in the field of biological analysis.Besides,it also develops new research directions for the design and application of azide-modified fluorescent probes.