Carbon Dots-based Fluorescent Nanoprobes: Fabrication And Their Applications In Cell Imaging And Enzyme Activity Evaluation

With the rapid development of bioscience,the determination of biomolecules(nucleic acid,proteins,enzymes,small molecules,etc.)in biological system attracted increasing attentions.Generally,the appearance and changes of biomolecules in the human body forebode the imbalance and lesion of human physiological functions,such as protein and nucleic acid associated with cells function and hereditary feature,marker molecules related to tumor and cancer,and small molecules related with the normal growth and development of body.Thus,the determination of relevant molecules in biological system is of great significance to prevent the biological disease in the initial stage of the biological change.In recent years,carbon nanomaterials such as carbon nanotube,graphene,and carbon nanoparticles inspired great interest due to their distinct physical and chemical properties.Moreover,carbon nanomaterials have been applied in biological analysis because of their excellent optical properties,biocompatibility,and so forth.Carbon dots,as new type of carbon nanomaterial,possess multiple advantages including low cost,tunable fluorescence emission,low cytotoxicity and so on.Therefore,the fabrications of carbon dots-based fluorescent nanoprobes for biological analysis have gradually become a host pot in analytical chemistry.However,only a few carbon dots-based fluorescent nanoprobes are applied in the analysis of biological molecules.Moreover,further modification and functionalized are usually required for the fabrication of these carbon dots-based fluorescent nanoprobes.Such a modification process is of ct only time-consuming,but also can reduce the sensitivity of analysis.Based on the objective of the biological analysis on basis of the interaction between carbon dots and targeted analytes,this dissertation emphatically developed fluorescent nanoprobes for the detection of folic acid and targeted imaging of cancer cells based on the interaction between aconitic acid-based carbon dos and folic acid;in addition,we fabricated a fluorescent nanoprobe for the evaluation of glutathione reductase activity and the screening of glutathione reductase inhibitors based on the regulation of fluorescence of carbon dots by Ag+.This dissertation consists of four chapters as follows:Chapter one: The classification and biological application of carbon nanomaterials were briefly described.In addition,the category,preparation strategies,physical and chemical properties,and applications in chemical analysis of carbon dots were briefly introduced.The applications of carbon dots in biological analysis were emphatically elaborated.Chapter two: The aconitic acid-based carbon dots(AA-CDs)with blue emission fluorescence were synthesized by a facile hydrothermal reaction of aconitic acid and ethylenediamine.The AA-CDs can be applied in biological analysis because of their good water solubility and excellent optical performance.The quantitative analysis of folic acid(FA)was performed based on the fluorescence quenching of AA-CDs by FA,with the detection limit of 40 nM.Then,the developed fluorescent nanoprobe was successfully applied for FA analysis in folic acid tablets,oats,milk,and fruit juice.Furthermore,a weak fluorescence probe FA-AA-CDs fabricated based on the electrostatic adsorption of FA onto AA-CDs was successfully used for fluorescence imaging of Hela,SMMC-7721 and A549 cells with different levels of folate receptor(FR)expression.The results showed that the fluorescence intensity of these three kinds of cells was in accordance with the expression level of FR,indicating the achievement of targeted imaging of cancer cells.Chapter three: The yellow fluorescence carbon dots(CDs)were synthesized by solvothermal carbonization of 1,2,4-triamininobenzene in formamide.The fluorescence of CDs can be quenched by Ag+ via the electronic transfer between CDs and Ag+.The glutathione reduced(GSH)that generated from the glutathione reducatase(GR)catalytic reduction of glutathione oxidized(GSSG)in the presence of ?-nicotinamide adenine dinuceotide 2'-phosphate reduced tetrasodium salt hydrate(NADPH)can take away Ag+ and recover the fluorescence of CDs.Herein,we developed a fluorescent nanoprobe for the evaluation of GR activity with the detection limit of 0.1 mU mL–1.The CDs-based fluorescent nanoprobe was then successfully used to monitor the inhibition of GR by a typical inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea(BCNU).Chapter four: On the basis of the study in chapter three,we developed the carbon dots-based system for the screening of glutathione reductase inhibitor.GR pretreated with inhibitor can not catalytically reduce GSSG to GSH to further recover the fluorescence of CDs/Ag+,by which the screening of GR inhibitor can be achieved in the light of whether the fluorescence of CDs/Ag+ recovery.Subsequently,the influences of the compounds with nitroso group,carbonyl,and thiocarbonyl on GR activity were systematically investigated for the screening of GR inhibitors,taking the GR inhibitors reported in previous literatures as the reference.