Synthesis Of Glycine Functionalized Graphene Quantum Dots And Construction Of Fluorescence Sensing

Graphene quantum dots(GQDs)as a new type of graphene materials with the large specific surface area,low toxicity,stable optical properties and good biocompatibility which make it as a new fluorescent probe has great application prospect.However the individual GQDs have the disadvantages of low fluorescence qunatum yield and low reactivity,greatly limits its application in sensing analysis.Therefore,in order to improve the performance of graphene quantum dots in fluorescence sensing,the surface of graphene quantum dots is functionalized.Glycine is the simplest amino acid with one carboxyl group,hydroxyl group and amino group.Such structure with rich functional groups makes it very easy to make non-covalent interaction other molecule which suggested great potential of GLY as a good functional molecule to improve the analytical performance of GQDs.Based on this,glycine functionalized graphene(GLYGQDs)was synthesized in the experiment.In this thesis,we focus on the synthesis and characterization of functionalized graphene quantum dots and their applications in fluorescence sensing:(1)Synthesis of GLY-GQDs and determination of tartrazine by inner-filter effectIn this work,highly photoluminescent glycine(GLY)functionalized graphene quantum dots(GQDs)(GLY-GQDs)were synthesized by a simple and green pyrolysis method employing ethylene glycol as carbon source,GLY as functional molecule.Using transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV and fluorescence spectrum of GLY-GQDs have been characterized.The assynthesized GLY-GQDs exhibited excellent water solubility with a fluorescence quantum yield of 21.7%,and in 0.1 mol/L NaCl,pH 2.0-11.0 PBS buffer solution and air atmosphere at room temperature for 60 days,fluorescence intensity change less than 5%.The UV absorption of tartrazine and the excitation and emission spectra of GLYGQDs were overlapped in the range of 314-508 nm.Based on the inner-filter effect,GLY-GQDs were used to detect lemon yellow fluorescence sensing system.Under the optimum experimental conditions,the detection range of the system was 33 nmol/L-13.3 ?mol/L,and the detection limit was 3.5nmol/L.Compared with other detection methods,the GLY-GQDs method is more sensitive than the other methods.(2)Determination of L-ascorbic acid by fluorescence off-on method based on the GLY-GQDsThe fluorescence of GLY-GQDs was intensively quenched by Ce4+ via forming non luminescent complexes of GLY-GQDs-Ce4+.When ascorbic acid(AA)was in presence,Ce4+ was reduced to Ce3+ and the fluorescence of GLY-GQDs regained.In the light of this theory,a simple AA sensor was fabricated without complicated,costly and time-consuming operations.Under the optimal conditions,the fluorescence recovery ratio and the concentration of AA has a linear relationship in the range of 0.03-17.0 ?mol/L and with a detection limit of 25 nmol/L which was one order higher sensitive than the reported methods.Furthermore,this established sensor system also shows a high selectivity toward AA over a wide range of common biological molecules.The proposed method was successfully applied for the AA detection in serum samples.All these suggested the potential of this GLY-GQDs based sensor in the clinical analysis.(3)Synrhesis of GLY-GQDs and determination of phosphate-containing metabolites by GLY-GQDsBecause of glycol is of low toxicity,in the process of heating would pollute the environment,so in this chapter,using citric acid as the carbon source,synthesized GLYGQDs by a simple and green pyrolysis method.The quantum dots xhibited excellent water solubility with a fluorescence quantum yield of 33.34%.Using transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV and fluorescence spectrum of GLY-GQDs have been characterized.The fluorescence of GLY-GQDs could be intensively quenched by Fe3+ via forming non-luminescent complexes of GLY-GQDs-Fe3+.Due to high affinity of iron ions to phosphate ions through well-known Fe-O-P bonds,the quenched fluorescence of the GLY-GQDs could be recovered in the presence of phosphate-containing molecules.Under the optimal conditions,the fluorescence recovery ratio was linearly proportional to the concentration of ATP in the range of 0.03-3.2 ?mol/L with a detection limit of 15 nmol/L which was one order higher sensitive than the reported methods.At the same time using the standard addition method made biological samples(cells and blood),linear,measured the concentration of phosphoric acid metabolites in cells and blood are: 2.19 mmol/L,4.29 mmol/L,in accordance with the literature reported.