A Self-assembled Fluorescent Probe With Monosubstituted BODIPY And HFBI-RGD: Synthesis,Characterization,and Biologic Properties

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes?BODIPYs?are well known for their outstanding features including high quantum yields,large extinction coefficient,photostability etc.However,critical defects including short emission wavelength,low water solubility and poor biocompatibility are urgently to be solved for the further application in fluorescence imaging.In this paper,BODIPY was chosen as framework and three monosubstituted BODIPY as signal part of the fluorescence probe were synthesized.Meanwhile,a novel targeting hydrophobin was introduced to encapsulate dyes by self-assembly,which producing fluorescence probe HFBI-RGD/BODIPY.?1?2,4-Dimethylpyrrole and methyl-4-formylbenzoate were used as the starting materials to synthesized BODIPY framework 1 via condensation reaction in acid environment,oxidation-reaction with DDQ and coordination reaction with BF₃·OEt₂successively.Subsequently,the strong electron-donating groups 2a-2c were introduced to C-3 position of framework by Knoevenagel reaction.The structures of dyes 3a-3c had been measured by ¹H NMR,¹³C NMR and HRMS and their optical properties had also been characterized.The results demonstrated that the strong electron-donating groups introduced to C-3 position of framework could extent the conjugation length,which tuned the emission to 650 nm.Moreover,dye 3b with the best coplanarity compared to dyes 3a and 3c owned the highest fluorescent quantum yield(?_3b=0.73),which was ascribed to the rigid structure limiting the free rotation and resulting in the least nonradiative energy loss.?2?Next,we turned the attention to the main factors which affected the spectral properties of protein nanocages.The optical properties were measured and the BODIPY structure was calculated and we speculated that hydrophobin with a certain vacuum structure was prepared by the means of ultrasonic agitation.This cavity might seriously affect the fluorescence properties of the dyes of different sizes which wrapped into the protein nanocages.?3?The properties of fluorescent probe were evaluated by cytotoxicity experiment,co-fucusing experiment and in vivo experiment.The data showed that the probes exhibited waek even negligible cytotoxicity to the U-87 cells at low concentration.When the cells treated with HFBI-RGD/?3a-3c?,more probes could get into cells,which was drawned from the cover area of fluorescence in the graphs.The results manifested that the HFBI-RGD/BODIPY possessed the ability of targeting the cancer cells to some extent.Fluorescence was observed in the tumor tissue whether in the real time-dependent fluorescence images or anatomic images,while no fluorescence in the control experiment.Notably,these results efficiently confirmed the capability of HFBI-RGD/BODIPY fluorescent probe to target the tumor.