Preparation And Application Of Graphene Quantum Dots

.Graphene quantum dots(GQDs),a new kind of nanomaterial with the combined properties of graphene and quantum dots,GQDs have shown numerous wonderful physical and chemical properties due to the pronounced quantum confinement and edge effects.GQDs are superior in terms of high specific surface area,high photostability against photobleaching and blinking,excellent biocompatibility,and low toxicity.For these reason,GQDs are proposed to be applicable in various fields,such as biological imaging,sensing,drug delivery,catalysis,and photovoltaics.The strategies for the preparation of GQDs can be divided into two major categories:top-down and bottom-up approach.Top-down splitting methods lack precise control of the morphology and size distribution of the products,what’ s more,sometimes require special instruments to operate.Bottom-up organic approach,however,is realized by pyrolysis or carbonization of small organic molecules or by step-wise chemical fusion of small aromatic structures molecules.These methods allow for excellent control of the properties of the final product.In this study,for the first time,ultra-small single-layer GQDs with blue fluorescence were prepared by the bottom-up method of pyrolysis of sodium citrate,and their physical and chemical properties as well as their biocompatibility were investigated.Its chemical stability,light stability,and low cytotoxicity apply it to the construction of cell imaging and ratiometric fluorescent probes.The paper will be divided into four chapters:Chapter 1:IntroductionA summary for the preparation methods of GQDs;the size,optical and electrochemical properties of GQDs are summarized;and the applications of GQDs in the fields of biomedicine,physical electricity,and environmental science are summarized.Chapter 2:Preparation,characterization and apply to cell imaging of graphene quantum dotsThe preparation method of graphene quantum dots has a significant effect on its performance.In this chapter,GQDs were prepared by the bottom-up method of pyrolysis and carbonize of sodium citrate,and the optical,structural and stability of GQDs were analyzed by UV,FL,fluorescence lifetime,quantum yield,FTIR,XRD,XPS and chemical analysis.Size and morphology characterized by HRTEM,TEM,AFM.The results show that the preparation method is simple and convenient,and can ensure the maximal unity of GQDs,and the average particle size and height of the obtained GQDs are 1.3 士 0.5 nm and 0.6 nm,respectively.It is a monolayer graphene structure with ultra-small size.It was applied to live cell imaging.The results showed that it was stable to cytoplasm and nucleus with highly recognizable.It was proved that the prepared GQDs have good chemical stability,light stability and low cytotoxicity.Chapter 3:Establishment of ratiometric fluorescent probe based on GQDs-BSA-AuNCs and application to mercury ion detectionGraphene quantum dots and gold nanoclusters exhibit good co-excitation fluorescence characteristics.In this chapter,a novel ratiometric fluorescent probe was constructed by simply mixing GQDs with BSA-AuNCs for detection of mercury ions.The mercury ion response ratio was well linear in the range of 2.5-30 μmol/L(R2=0.9949).),LOD = 50 nmol/L(3σ),RSD = 0.52%(Hg2+ concentration is 20μmol/L,n = 6).Finally,through the spiked recovery tests for treated tap water and filtered lake water samples,the results showed that the spiked recoveries for the low,medium,and high concentrations of tap water were 98.18%,104.07%,and 97.16%,the results of lake water were 99.51%,98,33%,and 97.08%,respectively,indicating that the GQDs-BSA-AuNCs probe was applied to actual workability and accuracy.The fact proves that this new type of ratio fluorescent probe adds a built-in calibration system,which is not interfered by external instrument voltage and test background,and increases the stability and application range of the probe.Chapter 4:Construction of ratiometric fluorescent probe based on GQDs-BSA/MPA-AuNCs,which applied to detection of hydrogen peroxide and glucoseTo verify that GQDs can be applied to a variety of co-excitation systems,ratiometric fluorescent probes.This chapter builds a new type of ratiometric fluorescent probe for the detection of H2O2 and glucose by simple mixing of GQDs with BSA/MPA-AuNCs.The experimental results show that for the detection of hydrogen peroxide,the linear relationship between the response signal ratio and the concentration of hydrogen peroxide in the range of 1-18 μmol/L(R2=0.9949),LOD=4.90 nmol/L(3σ),RSD= 1.09%(H2O2 concentration is 10 μmol/L,n=6).In the range of 1-15 μmol/L glucose detection showed a good linear relationship between glucose concentration and response signal ratio(R2=0.9948),LOD=29.12 nmol/L(3σ),RSD=0.33%(glucose concentration is 8μmol/L,n=10).By further comparing the spiked recovery test of actual serum samples with the standard HRP-TMB method,the results showed that the spiked recoveries of the serum at low,medium,and high concentrations were 102.63%,106.16%,and 101.91%,respectively.The comparison with the standard method showed that the relative deviations of the two detection methods for different serum samples ranged from-0.51%to 4.25%.Both experimental results indicated that the GQDs-BSA/MPA-AuNCs probe was applied to the actual implementation and accuracy.Therefore,it can be generalized that as long as there is a substance and GQDs co-excited,a ratio-type fluorescent probe system can be constructed to improve the stability and accuracy of the detection system.