Development Of Advanced Fluorescent Probes With Aggregation-Induced Emission Characteristics For Biomedical Applications

Fluorescence is one of the most commonly used techniques in biomedical study and detection.The properties of the fluorescent molecule directly affect the performance and application of fluorescent analysis and imaging.However,many conventional organic fluorescent probes can emit efficiently as isolated molecules.In the aggregate or solid state,their luminescence will be significantly reduced or even quenched.This common phenomenon is called aggregation-caused quenching(ACQ).The practical application of fluorescent probes has been affected by ACQ to varying degrees.In 2001,Professor Ben Zhong Tang’s group in the Hong Kong University of Science and Technology discovered a new class of fluorescent molecules that are distinct from traditional ACQ fluorogens.They don’t emit in molecularly dispersed state,but emit brightly in the aggregate state.They coined this unique phenomenon aggregation-induced emission(AIE)and proposed that the restriction of intramolecular motions(RIM)is the main molecular mechanism of AIE effect through systematic research.Compared with ACQ molecules,AIE probes have significant advantages such as high fluorescence intensity and high photostability because they are not limited by ACQ and low working concentration in practical applications.The unique mechanism of RIM also opens up new research fields for the development of sensors and fluorescent imaging.In the first chapter of this thesis,we designed and synthesized a novel fluorescent probe LC25.LC25 exhibits AIE characteristics,good biocompatibility,and mitochondria-targeting properties.Moreover,the good water solubility of LC25 makes it almost non-fluorescent in water.Imaging of cellular and fungal mitochondria can thus be achieved in a one-step,wash-free manner.We further found that fungi stained with LC25 showed different fluorescence changes under treatment with different drugs,which can potentially be used for antifungal susceptibility testing.All these merits make LC25 a promising tool for real-time fungal cell proliferation analysis,pharmacology research,and rapid antifungal susceptibility testing as a safe,mitochondrial membrane potential sensitive probe.In the second chapter,we developed a novel fluorescent probe IND-DABA with AIE effect.IND-DABA emits green fluorescence in lipids but emits bright red fluorescence as aggregates in water.Furthermore,the high fluorescence intensity,good biocompatibility,and excellent two-photon imaging performance enabling it to achieve two-photon lipid imaging in fixed and living cells,as well as in a mouse atherosclerosis model at the tissue level.Two-photon,high resolution lipid fluorescence imaging and quantitative analysis of the lipids in the plaque in situ can also be successfully achieved.In the third chapter,a biocompatible fluorogen TPE-PyN3 is reported for noninvasive imaging and sensing within living systems.TPE-PyN3 exhibits unique AIE attributes and high affinity to mitochondria,enabling it to achieve specific mitochondrial imaging and long-term cellular observing with excellent photostability both in vitro and in vivo.The high membrane penetrability of TPE-PyN3 allows all of the cells within the living zebrafish embryos to be morphologically visualized and reconstructed in 3D.Moreover,TPE-PyN3 is capable of indicating cell apoptosis because of its sensitivity to the change of mitochondrial membrane potential.In the fourth chapter,a novel "clickable" sensing platform for signal-on fluorescent detection of Cu2+has been developed based on the high regioselectivity of Cu(I)-catalyzed azide-alkyne click reaction(CuAAC)and the AIE-active molecules BATPE as the signal reporters.The CuAAC reaction causes a structural change of BATPE from molecularly dispersed to aggregate state in the presence of trace Cu2+,thus inducing a dramatic fluorescence "turn-on" response which can be judged with the naked eye.Under the optilum conditions,down to 0.5 μM Cu2+was successfully detected by naked eye,which makes it a promising sensor for on-site Cu2+ analysis in biomedical and environmental detection.In summary,a series of aggregation-induced emission probes were successfully designed and developed for biomedical applications,which has enriched the toolbox of AIE fluorogens for biotechnological applications in the areas of microbiological analysis,bio-imaging,and biosensing in living organisms.