Design,Preparation,and Applications Of PH-Sensitive Near Infrared Cyanine Fluorescent Probes

Cancer seriously threatens human life.Its early diagnosis and treatment is the most effective method to improve the cure rate.Fluorescence imaging has become a powerful tool for early diagnosis of tumor by virtue of its advantages such as non-invasive,real-time,high sensitivity and so on.Based on the weak acid microenvironment of tumor cells,the development of pH-sensitive probe which could specifically discriminate weak acid environment is expected to realize the general diagnosis of various tumors.Moreover,intracellular pH also plays an important role in physiological and pathological processes,thus it is important to develop fluorescent probes for the monitoring of intracellular pH value.Heptamethine cyanine probes have been widely applied in the fields of bioanalysis and imaging because its near-infrared excitation and emission wavelengths eliminate the background interference.Based on all above,the thesis aims to design and synthesize several near-infrared pH-sensitive fluorescent probes to monitor the fluctuation of intracellular pH,and the probes with excellent properties and appropriate pH-sensitive ranges were selected and applied in the specific imaging of tumor cells.On this basis,we further constructed ratio fluorescent probe,two-mode fluorescent probe and cyanine-contained fluorescent nanoprobes,and investigated their responses toward pH and application performances.1)Three pH-sensitive symmetric heptamethine cyanine probes 6,8,10 were designed and synthesized.Through the study of their spectral behaviors at different pH values,it was found that N-alkyl substituted symmetric cyanine 8 and 10 could be used to identify the pH changes in weak acid range,while non-alkyl substituted probe 6 could detect fluoride ions with high sensitivity and selectivity.2)A series of pH-sensitive asymmetric heptamethine cyanine probes 12-16 were designed and synthesized.Their spectroscopic properties at different pH value indicated that these fluorescent probes all belong to off-on type pH fluorescent probes and possess different linear response ranges toward pH value,which covered pH detection in the range of 2.53-6.45.Probe 16,containing the glucosamine group,has good water solubility and desired pH response range,and was further successfully applicated in the detection of intracellular pH fluctuations and specific imaging of cancer cells.3)Considering that the single fluorescence signal is easily affected by probe's concentration,environment and the apparatus,naphthalimide was introduced into pH-sensitive asymmetric cyanine as a reference fluorophore to construct a ratio pH fluorescent probe 18.Its ratio fluorescence has a good linear relationship with pH value in the range of 3.65-4.70,and further successfully used to monitor the fluctuation of intracellular pH.In order to complement the insufficient of different imaging modes,DTPA-like Gd³⁺ligand was introduced into asymmetric cyanine to obtain an optical/magnetic dual-mode pH probe,but its performance was not desired.4)In virtue of the advantages of nano fluorescent probes such as good stability and passive tumor targeting ability,asymmetric cyanine was introduced into covalent organic framework(COF)or carbon dot to develop nano fluorescent probes.COF Tp Pa-NH₂,containing amino groups,was successfully constructed,and it was found that Tp Pa-NH₂ and metal hybrid material Cu-COF both exhibited promising catalytic performance in Knoevenagel reaction,styrene oxidation and p-nitrophenol reduction.However,the hybrid material derived from cyanine and Tp Pa-NH₂ displays poor performance.Furthermore,carbon dot Cy CD and CDs-Cy were obtained from asymmetric cyanine by direct synthesis and two-step reaction,respectively.Both of them showed obvious response to pH change,but their dispersion stability,water solubility and sensitivity need to be further improved.