Preparation And Applications Of Carbon Dots And Metal Nanocomposite

Compared with traditional semiconductor quantum dots,carbon dots(CDs)as a new kind of carbon nanomaterials,have several advantages such as low toxicity,excellent photoluminescence(PL),chemiluminescence(CL)and electrochemiluminescence(ECL),good photostability,better biocompatibility and easy surface modification,and thus have been widely used in ion detection,environmental analysis,bio-imaging and biosensing.Recently,metal nanoparticles,especially those noble metal nanoparticles,have attracted more and more attention due to their excellent surface plasmon resonance effects.However,less attention has been paid to the studies on CDs and noble metal nanocomposties,especially the applications of the nanocomposites in analytical detections and biosensing.These new type of nanocomposites combining the advantages of both CDs and noble metal nanomaterials would have great potential applications in nanotechnology components,drug delivery,highly sensitive biosensors and analytical detection.In this paper,we explored utilizing a simple,fast and low cost method to prepare noble metal nanoparticles uniformly loaded CDs and their applications in analysis and detection.To be more specific,we studied simple and efficient,rapid and economic ways to fabricate nanocomposites of silver,gold respectively with unmodified and hydrazine modified graphene quantum dots(GQDs),an important kind of CDs.Then their structure characterization and performances were tested and evaluated.Finally,we applied them in the detection of small organic molecules and biomolecules by the means of surface enhanced raman scattering(SERS)and ECL,showing their promising application on biosensing and analytical detection.The thesis includes following four chapters.In chapter 1,literatures related to CDs,including their properties,synthesis methods,and applications were reviewed.Furthermore,brief introduction on the nanocomposties consisted of CDs and metal was included.The significance of this thesis was highlighted at the end of this chapter.In chapter 2,a simple method has been developed for the preparation of silver nanoparticles/carbon based quantum dots nano-hybrids(AgNPs/CDs).The small sized CDs with abundant of oxygen-containing functional groups adsorbed sliver ions firstly through ion exchange or coordination reactions.Then,during the reaction with NaBH4,Ag+ ions were reduced into AgNPs while the oxygen-containing functional groups were partially removed from the CDs.Thus,CDs were coated on the surfaces of the resultant AgNPs,leading to the formation of AgNPs/CDs nanocomosties.The residual oxygen-containing groups on the CDs made the obtained AgNPs/CDs highly dispersive and long-term stable in water.The resultant AgNPs/CDs showed a high SERS activity and can be used to constructed a sensitive SERS sensor for 4-aminothiophenol,with a wide dynamic range from 1�10-10 to 1�10-5 and a low detection limit of 5.Ox 10-11 M at S/N= 3.In chapter 3,hydrazide-modified graphene quantum dots(HM-GQDs)obtained by refluxing GQDs with hydrazine hydrate were hybridized with gold nanoparticles(AuNPs)through a redox reaction between HM-GQDs and AuC14-.The obtained nano-hybrids(HM-GQD-AuNPs)possess the unique electrochemiluminescence(ECL)properties of HM-GQDs and the easy self-assembly of bioconjugated AuNPs,which have great potential applications in biosensors.HM-GQD-AuNPs were modified on a glassy carbon electrode to develop a novel ECL immunosensor of carcinoembryonic antigen(CEA)as a model target analyte.Due to the increment of electron-transfer resistance after immunoreaction,the ECL intensity decreased as the concentration of CEA was increased.The linear response range was between 0.02 and 80 ng mL-1,and the detection limit was 0.01 ng mL-1.In chapter 4,a simple in-situ compositing process was used to synthesize HM-GQDs-AuNFs by reducing HAuC14 with NaHB4 under the conditions that HAuCl4 was exposed thoroughly to HM-GQDs and sodium citrate was used as the protectant.The as-prepared HM-GQDs-AuNFs exhibited strong and stable ECL activity,compared with that using gold nanoparticels.The nanocomposites were used for the construction of an ECL immunosensor to detect thrombin(TB).The result showed that the proposed immunosensor for TB had high specificity and long-term stability.The linear response range was found to be 0.01 to 40 nM and limit of detection was 5 fM.