Synthesis Of Fluorescent Doped Carbon Dots And Their Analysis Applications

Fluorescent carbon dots?CDs?constitute a fascinating class of recently discovered nanocarbons with a size below 10 nm and have attracted considerable research interest due to their excellent photostability,easily modified surface,low cost synthesis,and good biocompatibility.Especially,doped CDs have more uniqueoptical fluorescence properties than the pure CDs.Therefore,doped CDs as fluorescent probe form attractive applications in bioanalysis.In the thesis,we prepared three kinds of CDs fluorescence system through doping,which can sensitively analyze drug molecules curcumin,ascorbic acid?AA?,Cr???,and Co²⁺ ions,and?or?can be used for cell Imaging.Chapter 1:We briefly outlined the properties and synthesis of fluorescent CDs,and reviewed their research development on applications in analysis.Chapter 2:A facile,economical and green one-step hydrothermal method for N-CDs was presented by using citric acid as carbon source and urea as nitrogen source.The microstructure and photoluminescence properties were analyzed by HR-TEM,DLS,FTIR,UV-vis and fluorescence spectra.The as-prepared N-CDs possessed an average size of 5.23nm and exhibited high fluorescent quantum yield of 25.4%,good water solubility and excellent photostability.The maximum excitation and emission wavelengths of N-CDs were located at 360 nm and 445 nm.The curcumin possessed a wide absorption peak at around from 300 to 550nm,which showed quite precise overlapping with both the excitation and emission spectra of N-CDs.In the presence of curcumin,The fluorescence of N-CDs could be quenched dramatically.The fluorescence lifetime of the N-doped CDs was almost no change in the presence of curcumin.So the quenching might be caused by inner filter effect.The sensitive detection method of curcumin in aqueous solution was developed with the linear range of 2.0×10^-7?1.0×10^-5 mol/L and detection limit of 8.48×10^-8 mol/L?S/N=3?.The other common ions and related compounds in human body could not interfere detection of curcumin with good selectivity.The proposed method was successfully applied to the determination of curcumin in urine samples and the recoveries were 95.71-103.81%.Chapter 3:Choosing four kinds of representative green dry microorganisms biomass as the natural carbon source,including Saccharomyces cerevisiae,Escherichia coli,Staphylococcus aureus,Aspergillus niger,fluorescent nitrogen/phosphorous/sulfur co-doped carbon dots?N,P,S-CDs?have been synthesized through a facile one-step hydrothermal method.Using quinine sulfate as a standard,the respective QY values of four N,P,S-CDs were calculated.Finally we chose N,P,S-CD_Sac as the main research object in the next work considering its relatively high QY and the more easier culture of Staphylococcus aureus.The size and morphology of the N,P,S-CD_Sac were characterized by HR-TEM and DLS.The results indicated the diameters of N,P,S-CD_Sac was in the range of 3.85±0.50 nm,and had a lattice spacing of 0.267 nm.The elemental analysis,XPS and FTIR results confirmed that N,S and P were doped onto the surface of the N,P,S-CD_Sac successfully.The UV-vis and fluorescence spectra showed that the maximum excitation and emission wavelengths of N,P,S-CD_Sac were located at 350 nm and 445 nm.In the presence of Cr?VI?,the fluorescence of N,P,S-CD_Sac could be quenched dramatically,and when adding into ascorbic acid?AA?,the fluorescence could be recovered.Based on quenching and recovery of N,P,S-CD_Sac fluorescence,we developed N,P,S-CD_Sac as a dual-channel fluorescent probe for intracellular Cr?VI?and AA detection.The linear ranges for Cr???and AA were 0.5-50 ?M and 5-300?M,respectively.The detection limits?S/N=3?were 42nM for Cr???and 2.7?M for AA.According to the confocal fluorescent imaging of human cervical cancer SiHa cells,N,P,S-CD_Sac can penetrate into the cell and enterthe cytoplasm and nucleus,suggesting pleasurable promise for bioimaging.Chapter 4:We developed a facile zero-energy consumption strategy for the fabrication of highly fluorescent nitrogen/phosphorus-co-doped carbon dots?N,P-CDs?and demonstrate their applications for cellular imaging and Co²⁺ sensing.The zero-energy consumption synthesis method using sucrose as carbon precursor which was carbonized by the neutralization exothermal reaction with ethylenediamine and concentrated phosphoric acid.The HR-TEM,elemental analysis,XPS,FTIR results revealed that the average size of N,P-CDs with a lattice spacing of 0.192 nm was 3.44±0.20 nm,and N and P were doped onto the surface of the N,P-CDs successfully.The UV-vis and fluorescence spectra showed that the maximum excitation and emission wavelengths were located at 410 nm and 505 nm with a QY of 5.77%.MTT results indicated that N,P-CDs had ultralow toxicity,and could be superior fluorescent bioimaging agents in cells.In the presence of Co²⁺ ,the fluorescence of N,P-CDs could be quenched dramatically,and the other common metal ions could not interfere detection with good selectivity.Thus we established a high selective and sensitive detection method for Co²⁺ .The method allowed a linear range from 0.05 to 10?M for the determination of Co²⁺ ,and the detection limit was 59 nM?S/N=3?.Chapter 5:We summarized the rearch results about the doped CDs as fluorescent probes for applications in ions and pharmaceutical analysis and cell imaging,and the future possible work steps were speculated.