Construction Of Functionalized Fluorescent Carbon Dots And Their Biological Applications

Carbon dots（CDs）are fluorescent carbon-based nanomaterials with unique optical properties,excellent physical and chemical features.CDs exhibit good biocompatibility,highly photobleaching resistance,good stability and excellent water solubility which show great significance and broad application prospects in various fields such as biology,chemistry,physics,medicine,environment,etc.Recently,the research on CDs has received more and more attention.A lot of work has carried out around the improvement of synthesis methods,the discussion of luminescence mechanism,the control of luminescence properties and the expansion of practical applications.In order to further promote the research progress,we are focused on the construction of functionalized fluorescent carbon dots and their biological applications.We conduct our research from the following three chapters:1 A novel turn-on fluorescence assay for UA detection has been developed based on fluorescence resonance energy transfer（FRET）between CDs and manganese dioxide（MnO₂）nanosheets.The MnO₂ nanosheets can adsorb CDs to form nanocomposites with the fluorescence of CDs quenched via FRET.The fluorescence will be recovered when UA introduced into the sensing system due to the decomposition of MnO₂ nanosheets to Mn²⁺.Under optimized condition,the fluorescence signal was linearly related to UA concentration in the range of 0.1-200μM,and the detection limit was as low as 45 nM.Moreover,this developed assay was successfully applied for human urine sample analysis,which indicated that this strategy could be an efficient tool for clinical disease diagnosis.2 The dual-emitting（472 nm and 560 nm）pH-responsive CDs have been synthesized using folic acid and o-phenylenediamine rich in electronegative atoms as carbon and nitrogen sources by the hydrothermal method.The synthesized CDs exhibited excellent water solubility,low cytotoxicity and good photostability.CDs displayed obvious pH-sensitive property due to the protonation and deprotonation of amino and carboxyl groups on the surface of it.In the buffer solution,the CDs exhibited excellent pH-sensitive property in a wide range of 3.5-10.0 at 472 nm and in a range of 4.5-6.5 at 560 nm.The two pK_a values of CDs are 7.35 and 5.37,respectively.In addition,CDs were successfully used as pH probes for monitoring intracellular pH in HeLa cells,proving its applicability in cells.3 Fluorescent CDs with long-wavelength emission have been prepared by the microwave method using rifampicin for the first time.The CDs exhibited strong emission at 556 nm with a high quantum yield of 34%.The surface state and the large conjugated structure of the CDs have synergistic effect on their strong long-wavelength emission.CDs have successfully used in HeLa cells imaging due to its good solubility,long-term stability and low toxicity.The long-wavelength excitation and emission of CDs can reduce background fluorescence and tissue damage,thus it is expected to be further applied in cell and tissue imaging.In addition,owing to the excellent antibacterial activity of rifampicin,CDs also maintained good antibacterial property and confirmed by the antibacterial experiments of Escherichia coli.