Research On Synthesis And Photoluminescence Property Of Functionalied Graphene Quantum Dots

With the rapid development of nanotechnology and biotechnology,nanoparticle-based drug delivery systems have shown promising impact to improve the pharmacological and therapeutic properties of drugs.Nano-structure drug carriers,which are easily modified to achieve a spatial and temporal control of drug delivery and release,are the core of a drug delivery system.Fluorescent carbon nanoparticles,such as carbon nanotubes,carbon dots and graphene nanaoribbons,have been founded and widely investigated,with the advent of structural diversity,multi-functionality,especially low toxicity and bright instinct fluorescence,to replace organic dyes and traditional semiconductor quantum dots for biomedical applications.Graphene quantum dots(GQDs),as a new generation of carbon nanoparticles,with fascinating properties of graphene,such as large surface area,excellent mechanical ductility,good chemical stability and biocompatibility,have been constantly applied in electrochemical biosensors,bioimaging and targeted drug delivery.The research of GQDs is still in the initial stage so far,there are significant drawbacks including complex production,low photoluminescence property,low quantum yields and so on.In terms of biological application,researchers,both domestic and overseas,have conducted various experiments and succeeded in infiltrating GQDs into cytoplasm labeling and carrying medicine into cells.However,for anti-cancer drugs,which are meanly effected to interfere with DNA replication in the cell nucleus,it is of lasting significance for the purpose of improving the effectiveness of anticancer drugs and reducing their side effects to develop a nucleus-targeted drug carrier.Herein,we developed a simple solvothermal method to prepare discomposed PEI,graphene quantum dots and PEI functionalized GQDs,respectively.The morphologies,microstructures and optical properties were investigated and discussed,and the biocompatibility were also studied and compared.In addition,drug delivery systems with the as-prepared D-PEI and GQDs-PEI as carriers were built,respectively,and the intracellular uptakes were studied.The main conclusions are as follows:1.Discomposed polyethylenimine(D-PEI)with bright green intrinsic photoluminescence is obtained by solvothermal treatment of branched PEI in ethanol solvent.The result shows that the as-prepared D-PEI are well dispersed,and most of the structure character of PEI are retained.A marked photoluminescent behavior of the D-PEI was noticed,and the strongest emission peak is located at 518 nm.It is also confirmed that the D-PEI have excellent photoluminescence properties,including a high quantum yield of 8.66% and a long fluorescence lifetime of 6.86 ns.2.Ultrasmall graphene quantum dots surface passivated with branched PEI(GQDs-PEI)were synthesized with a new convenient solvothermal method,which combined the “top-down” cutting,reducing and functionalizing graphene oxide(GO)sheets in one step.Bared GQDs were also prepared in the same procedure.The morphology and structure of GQDs-PEI and GQDs were investigated by TEM,FT-IR and XRD spectroscopic analysis.The result shows that the collected GQDs-PEI were distributed in a narrow size between 1 and 3 nm with an average diameter of 1.66 nm.Compared with the unfunctionalized GQDs,the GQDs-PEI has achieved a better optical property including high quantum yield(maximum value is 53.0%)and narrow emission spectral features.To obtain a better fluorescent property of the GQDs-PEI for further application in biological labeling,the preparation conditions,reaction time,temperature and p H value were explored,the optical properties have been further compared and discussed.In consideration of factors such as time and cost,when the p H value of the mixture solution set to 12,the preparation temperature ascend to 200 °C,and after 20 hours reaction in autoclave the as-prepared GQDs-BPEI can achieved a higher UV absorbency and better PL properties.3.To investigate the biocompatibility of the as-prepared GQDs and GQDs-PEI,biological experiments are conducted.The MTT assays of cell viability studies suggested that the GQDs-PEI do not impose a considerable toxicity of MG-63 cells compared to the GQDs.When MG-63 cells were incubated in 100 ?g/m L GQDs-PEI for 48 h,the cell viability was still about 80%.From the in vitro bioimaging experiment we further founded that after 6 h incubation in same concentration of GQDs-PEI and GQDs,the MG-63 cells are still in good condition.Further more,different with the GQDs family members which are mainly localized in the cytoplasm region,cell images observed by confocal microscope have demonstrated that the GQDs-PEI are mainly aggregated in the nucleus region.This result suggests that the GQDsPEI may find exciting applications in the nucleus labeling,diseased phenotypes diagnosing and the targeted therapy of tumor cells.4.Since the outstanding membrane penetration ability of PEI,the as-prepared D-PEI and GQDs-PEI are conjugated with DOX to build nucleus targeted drug delivery systems,respectivly.By loading on anti-cancer drug DOX,it is proved that both the drug loading and release property are improved after conjugated with GQDs.Moreover,the in vitro cellular uptake experiment with He La cells shows that both the D-PEI/DOX and GQDs-PEI/DOX drug delivery systems can efficiently delivery the anti-cancer DOX to the nucleus region of tumor cells.Moreover,the GQDs-PEI/DOX presents better nucleustargeted ability and achieves a stronger cytotoxicity,suggesting a promising application in biological and medical areas.