Carbon-based Quantum Dots:Synthesis,Property And Application In Drug Delivery System

Carbon-based quantum dots have widely been used in the field of nanomedicine,tissue imaging and precision medicine,due to their good biocompatibility,low toxicity and bright fluorescence.In this thesis,the functionalized carbon quantum dots?CQDs?and graphene quantum dots?GQDs?were prepared by hydrothermal method,originating from citric acid and graphene oxide.The structure,photoluminescence?PL?property and photothermal effect of the carbon-based quantum dots were studied and applied to design a multi-functional and stimuli-responsive nanoplatform in the biomedical field.The main research contents of the thesis were as follows:Firstly,one-pot hydrothermal synthesis of nitrogen-doped carbon quantum dots surface-modified by PEI?PEI-N-CQDs?was carried out from citric acid and polyethylenimine?PEI?in N,N-dimethylformamide.The products were purified through precipitation method.The synthesized PEI-N-CQDs with crystal size about 5nm exhibited a spherical core-shell shaped structure with sp² carbon as nano core and amorphous sp³ carbon and PEI as hydrophilic shell.PEI-N-CQDs in aqueous solution showed blue fluorescence even at a low concentration?0.5?g/ml?,and excitation-dependent PL behavior.The fluorescence properties of PEI-N-CQDs were sensitive to environmental pH value.The fluorescence intensity of PEI-N-CQDs was decreased and the maximum emission peak was moved in acid pH environment,but the PL intenstity was significantly enhanced under alkaline condition.In addition,the aggregation of PEI-N-CQDs in organic solvents induced the change of PL emission.Secondly,based on the ABA amphiphilic triblock copolymers polylactide-block-poly?ethylene glycol?-block-polylactide with o-nitrobenzyl esters as the photocleavable block-linker?defined as PLNENL?,a fluorescent labeled drug delivery carrier model was constructed by loading doxorubicin?DOX?and PEI-N-CQDs through self-assembly.The drug released was obviously increased from DOX-loaded micelles in vitro after UV irradiation,and could be controlled by the relative content of o-nitrobenzyl esters in polymers.Moreover,PEI-N-CQDs was encapsulated in this drug carrier to form micelle composites.The nano composite was induced to release CQDs by UV irradiation,and exhibited a blue fluorescence emission peak under the exciting at 360nm.Finally,Hummers method with appropriate optimization was used to yield graphene oxide?GO?.The oxidation degrees of GO precursor were controlled via the type of phosphate intercalators?KH₂PO₄,NaH₂PO₄,LiH₂PO₄ and H₃PO₄?.The results indicated GO-K showed the high-quality oxidation due to 53.18%oxidized carbon and interlayer spacing at 9.87?.The GO-K was reduced thermally and then oxidized to yield graphene oxide quantum dots?GOQDs?in strong acid environment.Subsequently,the functionalized graphene quantum dots?PEI-GQDs?was prepared by hydrothermal method.Both GOQDs and PEI-GQDs exhibited the small sized graphitic carbon structure with highly crystalline quality,yellow fluorescence and excitation-dependent multicolor emission.Furthermore,under NIR laser irradiation at 808nm,the conjugated?system of GQDs absorbed photons to generate heat,resulting in the fast temperature growth in surrounding environment,especially the temperature increment of PEI-GQDs was exceeded 60°C within 6min.GQDs showed excellent photothermal efficiency and stability,which exhibited potential application in multifunctional nano-platform for photothermal therapy.