Design,Synthesis Of Nitrogen Doped Carbon Based Quantum Dots And Carbon Dots Based Nanocomposite And Their Application In Biochemical Sensors

Carbon based quantum dots become a hot research topic due to their excellent physical and chemical properties,including small particle size,wide excitation wavelength range,highly tunable photoluminescence property,high quantum yield,good water solubility,chemical inertness,ease to be functionalized with biomolecules,and excellent photostability.Compared with other quantum dots,carbon based quantum dots possess better biocompatibility and low toxicity.Carbon quantum dot may be also promised various applications in biosensing,drug delivery,and bioimaging.Carbon based nanocomposite,such as carbon based metal nanoparticle and metal oxide nanoparticle hybrids,exhibit excellent catalytic activity,which were constructed and shown great potential applieations.Carbon based quantum dots,as a stabilizer and substrate,were used to prepare carbon based nanocomposite,which facilitate the electron transform and electric conduction of carbon based nanocomposite.Compared with single carbon based quantum dots and composite nanoparticles,carbon based nanocomposites have some unique physical and chemical properties,including some advantages in electrical,magnetic and nonlinear optical properties.In this thesis,nitrogen doped carbon based quantum dots with strong electron donor ability or reduction performance were synthesized by means of chemical doping.Fluorescence sensor based on nitrogen doped carbon based quantum dots were proposed for application in the detection of metal ions and pH in the intermal and external cell as well as cell imaging.Then,carbon based nanocomposite with horseradish oxidase activity were also synthesized by as-prepared nitrogen doped carbon based quantum dots,which were used as stabilizer and reducing agent.Carbon based nanocomposite were applied in the identification of dihydroxyhenzene and phenylenediajine isomers as well as the chemiluminescent detection of disease markers in biological samples.Specific research content as following:1.A facile one-pot solidphase synthesis strategy for N-doped GQDs was proposed using citric acid(CA)as the carbon source and 3,4-dihydroxy-L-phenylalanine(L-DOPA)as the N source.The as-prepared N-GQDs with oxygen-rich functional groups are uniform with an average diameter of 12.5 nm.Because of the introduction of nitrogen atoms,N-GQDs exhibit excitation-wavelength-independent fluorescence with the maximum emission at 445 nm,and a high quantum yield of 18%is achieved at an excitation wavelength of 346 nm.Furthermore,a highly efficient fluorosensor based on the as-prepared N-GQDs was developed for the detection of Hg2+ because of the effective quenching effect of metal ions via nonradiative electron transfer.This fluorosensor exhibits high sensitivity toward Hg2+ with a detection limit of 8.6 nM.The selectivity experiments reveal that the fluorescent sensor is specific for Hg2+.The practical use of the propsed sensor based on N-GQDs for Hg2+ detection was demonstrated in river-water samples.2.The facile hydrothermal synthesis strategy was applied to synthesize multi heteroatoms(nitrogen and phosphorus)co-doped carbon nanodots(N,P-CDs)using glucose as carbon source,and ammonia,phosphoric acid as dopant,respectively.The size of as-prepared N,P-CDs are from 2.2 to 3.5 nm.N,P-CDs exhibit excitation-wavelength dependent fluorescence with the maximum emission at 437 nm,and a high quantum yield of 30%is achieved at an excitation wavelength of 336 nm.Compared with CDs,the multi heteroatoms doped CDs resulted in dramatic improvement in the electronic characteristics and surface chemical activities.Therefore,the N,P-CDs prepared as described above exhibited a strong blue emission and a sensitive response to Fe3+ because of the covalent bond between phosphate radical and amino group on N,P-CDs surface and Fe3+.The fluorescent sensor of the N,P-CDs was then applied to sensitively identify Fe3+,using a detection limit of 1.8 nM.Notably,the prepared N,P-CDs possessed negligible cytotoxicity,excellent biocompatibility,and high photostability.It was also applied for detection of Fe3+ without labels in biological samples and the fluorescence imaging of intracellular Fe3+.3.A nitrogen-rich functional groups carbon nanoparticles(N-CNs)based fluorescent pH sensor with broad-range responding were prepared by one-pot hydrothermal treatment of melamine and triethanolamine.The size distribution of the as-prepared N-CNs was mainly in the range of 3 to 7 nm with an average size of 5 nm.The as-prepared N-CNs exhibited the optimal emission peak at 440 nm with an absolute quantum yield of 11.0%,and possessed a broad pH responding property.A clear decrease of the fluorescence intensity could be observed and a good linear relationship was achieved as the pH increased from 3.0 to 12.0.The possible mechanism for the pH-sensitive responding of N-CNs was ascribed to photoinduced electron transfer(PET).The cell toxicity experiment showed that the as-prepared N-CNs exhibited low cytotoxicity and excellent biocompatibility with the cell viabilities of more than 87%.The proposed N-CNs based pH sensor was used for pH monitoring of environmental water samples,and pH fluorescence imaging of live T24 cells.4.The extraordinary reduction properties of as-prepared N-GQDs are attributed to the nature of the surface oxygen-containing functional groups.Based on it,a room temperature reducing agent-free strategy for the synthesis of a nitrogen-doped graphene quantum dot-silver nanoparticle(N-GQD/AgNP)hybrid was presented.In this strategy,N-GQDs were used as a reducing agent and stabilizer for the formation of the N-GQD/AgNP hybrid.The N-GQD/AgNP hybrid exhibits good dispersity and outstanding catalytic ability toward the oxidation of catechol(CC)and hydroquinone(HQ)by Ag+.In the presence of the N-GQD/AgNP hybrid,the reduction of Ag+ by CC and HQ was improved.CC enhanced the absorbance of the N-GQD/AgNP-Ag+ system the most,and HQ followed,while resorcinol(RC)had only a little effect on the absorption intensity of the system.Thus,a sensitive and selective colorimetric sensing method based on the N-GQD/AgNP-Ag+ system was developed for the discrimination of CC,HQ and RC.A good linear relationship was obtained from 0.1 to 15.0 μM for CC and from 0.3 to 20.0 μM for HQ.The detection limits of CC and HQ were 0.03 and 0.1 μM,respectively.In addition,the proposed method also shows a high selectivity for the detection of CC and HQ,and appreciable changes in color of the N-GQD/AgNP-Ag+system toward CC,RC and HQ were observed.5.A reducing agent-free strategy for the synthesis of a Fe3O4 nanoparticle/nitrogen-doped graphene quantum dot hybrids(Fe3O4/N-GQDs)was reported.In this strategy,Fe3O4/N-GQDs were facilely prepared by the hydrothermal treatment of Fe3+/N-GQDs solutions under alkaline conditions without other regents.The prepared Fe3O4/N-GQDs exhibited outstanding peroxidase-like activity and were stable under a wide range of pH values and temperatures.Therefore,a sensing platform based on Fe304/N-GQDs for the visual discrimination of phenylenediamine isomers was proposed.The phenylenediamine isomers(o-phenylenediamine,m-phenylenediamine,and p-phenylenediamine)were discriminated through the H2O2-mediated oxidation reaction using Fe3O4/N-GQDs as novel peroxidase mimics,which resulted in appreciable color changes.A good linear relationship from 1 to 90μM and a detection limit of 230 nM for o-phenylenediamine was achieved,and the linear relationship for p-phenylenediamine was from 2 to 70 μM with a detection limit of 530 nM.6.A practical and simple strategy for synthesis of cuprous oxide/nitrogen doped graphene quantum dot hybrids(Cu2O/N-GQDs)was presented.In this strategy,the green synthesis of N-GQDs was conducted by citric acid used as the carbon source,and 3,4-dihydroxy-L-phenylalanine used as nitrogen source.Then,the prepared N-GQDs were used as stabilizer and reducing agent to synthesize CuaO/N-GQDs.The as-prepared Cu2O/N-GQDs showed good stability,dispersion and horseradish peroxidase activity,which can catalyze the oxidation of luminol by H2O2 generating chemiluminescence.Compared with HRP’the outstanding horseradish peroxidase activity of Cu2O/N-GQDs were stable under a wide range of pH values and temperatures.Therefore,a chemiluminescence sensing based on Cu2O/N-GQDs was proposed and applied to the detection of H2O2 and uric acid in biological samples.The detection limit of H2O2 is 1.1×10-7 M,and the detection limit of uric acid is 4.1×10-8 M.The chemiluminescence sensing based on Cu2O/N-GQDs was of simple preparation,high sensitivity and selectivity.