Preparation And Analytical Ppplications Of PEI-Modified Fluorescent Carbon Dots

Carbon dots are fluorescent nanoparticles developed in recent years.Compared with traditional organic fluorescent dyes,carbon dots have advantages such as high fluorescence intensity,good light stability,photobleaching resistance,which make them excelent in analysis,biosensing,and bioimaging applications.The main contents of this thesis include the following two aspects:1.The amide-modifiedPEI was prepared by using hyperbranched polyethyleneimine?PEI?reacted with acetic anhydride under certain conditions.Then,PEI-modified fluorescent carbon dots were prepared by a hydrothermal method using citric acid as a carbon source reacted with modified PEI at a certain temperature.Under optimal conditions,that is 0.3 g modified PEI,0.3 g citric acid and 5 mL distilled water heated at 180?for 2h,PEI-modified fluorescent carbon dots with a quantum yield up to 43%were obtained.Moreover,the effects of pH,ionic strength and UV exposure time on the fluorescence stability of carbon dots were also investigated.The fluorescent carbon dots were characterized by ultraviolet visible spectroscopy,fluorescence spectroscopy,infrared spectroscopy and transmission electron microscopy.2.A"off-on"fluorescence probe for the detection of thiols was designed based on the interaction between fluorescent carbon dots,metal ions and thiols.First,due to the complexation of the functional groups such as-NH₂ and-COOH on the surface of the modified fluorescent carbon,Fe³⁺or Hg²⁺quenched the fluorescence of the fluorescent carbon dots.Then,the fluorescence of the carbon dots can be recovered by continuously adding L-cysteine?L-Cys?or reduced glutathione?GSH?due to the stronger interaction between thiol and metal ions.It was found that there was a functional relationship between the fluorescence recovery intensity and the concenteation of L-Cys and GSH.The probe was applied to detect GSH in onion sample and the recoveries were 96%¹03.7%and RSD was 2.7%³.4%.