Near-Infrared Fluorescent Probes Based On Hemicyanine Derivatives: Design, Synthesis And Applications In Bioimaging

In these decades,with the advancement of the knowledge in bioimaging,near-infrared?NIR?fluorescence imaging has been widely applied in many fields,such as tumor diagnosis and therapeutics,biomolecular detection and intracellular microenvironment monitoring.Fluorescence imaging in the NIR region has unique advantages.It can effectively reduce the absorption and scattering of biomolecules for the excitation and fluorescence signals,which can increase the penetration depth in biological samples.It can also avoid the inerferences from biological tissues to improve signal-to-noise ratio,and reduce the photo-damage to the samples for the use of light source in NIR region with long wavelength and low frequency.Therefore,the development of NIR fluorescent probes with different structures and functions has been one of the research hotspots in the field of fluorescence imaging.Organic fluorescent dyes,as a kind of NIR fluorescent probes,have received muche research interest due to their small molecular size,feasible functional modification,and easy design and synthesis.However,the applications of NIR dyes are restricted for low targetabilities and poor photostabilities,which limits their utilization in achieving subcellular structure targeting and detection of specific biomolecules.In this thesis,through exploring the structural modification towards targeting endoplasmic reticulum?ER?,a NIR hemicyanine fluorescent probe was designed and synthesized with high ER targetability.Meanwhile,a NIR boron complex probe based on hemicyanine skeleton was obtained for real-time monitoring the pH fluctuations in lysosome.Firstly,the ER targetability of hexyl chain with moderate lipophilicity was confirmed through systematically investigating and analyzing ER-targeted probes.Then the hexyl chain was applied in hemicyanine and a NIR fluorescent probe mCy-ER was designed with moderate lipophilicity,appropriate amphipathy,medium-sized conjugated system and positive charge.The absorption and emission of probe mCy-ER are both at NIR region and it has a very low toxicity towards living cells.Importantly,the results of its colocalization experiments with a commercial ER-targeted probe demonstrated that probe mCy-ER exhibited high targetability towards ER,providing a molecular platform for the construction of functional ER-targeted probes?Secondly,a NIR boron complex probe?HCy-BIZ-BF₂?based on hemicyanine skeleton was utilised to detect varied pH in lysosome and in vivo.It was proved that HCy-BIZ-BF₂ bears excellent pH responsibility,lysosome targetability and high intracellular photostability.By detecting the exogenous cellular pH,the linear relationship between the fluorescence intensity of HCy-BIZ-BF₂ and the changed intracellular pH was confirmed.Then,it was successfully applied for real-time monitoring the pH fluctuations in lysosome,realizing the quantitative visualization of lysosomal pH increasing under the stimulation of choloriquine.It is worth mentioning that,when used for detection of pH in mice model,the fluorescent signal of the probe HCy-BIZ-BF₂ in the endermic parts with different pH value shows obvious difference,which reveals its potentiality in application for in vivo imaging.