Preparation Of Graphene Quantum Dots And Its Application In Biomedical Detection

Whether in medical testing or environmental monitoring,quantitative analysis of molecules is indispensable,which requires researchers to develop convenient,fast,sensitive and highly selective analytical methods.Fluorescent nanoprobes have received widespread attention in the fields of chemical sensing as well as biological and drug molecular recognition due to their advantages of high sensitivity and selectivity,without the need for large and expensive instruments.In recent years,graphene quantum dots?GQDs?have been used by many researchers in construction of fluorescent nanoprobes due to their excellent photoluminescence properties,good chemical inertness,excellent biocompatibility,and low biological toxicity.One can change the synthesis method to prepare GQDs with different emission wavelengths;or use its larger specific surface area and rich functional groups to further functionalize its surface to meet the needs of detection of different substances.Although there have been many reports based on GQDs sensing platforms,most of these sensing systems have to undergo complex material synthesis and modification,use highly toxic reaction materials.To this end,this paper uses green and low-toxicity raw materials to synthesize GQDs,modify or functionalize them by a simple method,construct a series of fluorescent nanosensors,and explore its application in detection of drugs,small molecules of life,and macromolecular enzymes.The specific content is as follows:In chapter I,we first briefly introduced the discovery process of graphene quantum dots,and then systematically introduced its basic properties,luminescence mechanism,quenching mechanism,preparation method and its application in fluorescence analysis.And elaborated the research purpose and content of this thesis.In chapter II,we designed a bleomycin detection system based on the quenching effect of carcinoembryonic antigen on N-GQDs and cleavage of ssDNA by bleomycin-Fe²⁺.First,we used citric acid and ammonia as raw materials to synthesize nitrogen-doped graphene quantum dots?N-GQDs?.Carcinoembryonic antigen ssDNA is connected to the carboxyl group through?-?stacking,and is closely adsorbed on the surface of N-GQDs,thereby effectively quenching the fluorescence of N-GQDs.Bleomycin cuts specific sites with the help of Fe²⁺,irreversibly degrades ssDNA,releases N-GQDs,and restores fluorescence.Based on the above mechanism,we constructed a"turn-off-on"mode bleomycin quantitative detection system and used it in the detection of bleomycin in serum with satisfactory results.In chapter III,based on the quenching effect of paracetamol?PAR?oxidation products on the fluorescence of GQDs and the reducing properties of ascorbic acid?AA?,we constructed a detection system for PAR and AA.First,we modified polypyrrole?PPy?on the surface of GQDs to obtain PPy-GQDs composites.The material has three times the fluorescence performance of unmodified GQDs.The PAR is oxidized by tyrosinase to obtain the product N-acetyl-p-benzoquinone?4-AOBQ?,which can effectively quench the fluorescence of PPy-GQDs.When 4-AOBQ was reduced by AA,the fluorescence intensity of the system recovered.The quenching and recovering fluorescence intensity of PPy-GQDs are directly proportional to the concentrations of PAR and AA within a certain range,respectively.This method was successfully applied to the determination of PAR and AA in human serum.In chapter IV,we propose a new fluorescent sensor based on nitrogen-doped graphene quantum dots?N-GQDs?for the detection of H₂O₂ and various human metabolites?cholesterol,glucose,lactic acid,and xanthine?.Hg²⁺can be adsorbed on the surface of N-GQDs by electrostatic effect,which causes the fluorescence quenching of N-GQDs.In the presence of cysteine?Cys?,Hg²⁺binds to Cys and is released from the surface of N-GQDs to restore the fluorescence of N-GQDs.H₂O₂produced by the enzymatic oxidation of human metabolites converts two molecules of Cys into one molecule of cystine,which cannot bind to Hg²⁺,and the fluorescence of N-GQDs is quenched again.According to above mechanism,we constructed a"turn-on-off"sensor based on N-GQDs and applied it to the detection of H₂O₂ and metabolites in human serum with good results.