Fabrication And Analytical Application Of Carbon Quantum Dot

The unique properties of CDs,such as adjustable luminescent properties,excellent physical and chemical properties,high stability,good biocompatibility and small size,have manifested a huge application prospect and meanwhile gained researchers'tremendous attention.In this paper,3different types of CDs were fabricated via one-step doping way,after which the synthesized CDs were characterized by modern analysis methods,and then were applied for the building of chem-and bio-sensors and the application research of bio-imaging.Chapter 1:The first chapter presents a review on CDs.We summarized the research progress of synthesis methods of CDs,the physical and chemical properties of CDs and the application in analytical detection,bio-imaging and drug delivery.Chapter 2:Nitrogen and sulfur co-doped CDs?N,S-CDs?are produced by one-step hydrothermal treatment of acid fuchsine.The fluorescence of N,S-CDs are enhanced by introducing nitrogen and sulfur atoms,which emitted intense yellow fluorescence with the fluorescence quantum yield up to 9.9%.N,S-CDs are characterized via modern analytical methods,and then it is found that the average diameter of the syntherized N,S-CDs is about 3 nm.N,S-CDs possess stable luminescent properties and the abundant carboxyl,amino and sulfydryl functional groupsChapter 3:Based on the above mentioned N,S-CDs,the high selective and sensitive fluorescent chem-nanosensor has been built for label-free determination of Cur and pH.The fluorescence of N,S-CDs will be dramatically quenched by Cur,owing to the electrostatic interaction and hydrogen-bond interaction.The limit of detection can arrive at 81 nmol/L Cur,and the range of linearity is 0.5-20?mol/L Cur.Furthermore,a satisfactory result was obtained when applying the as-constructed fluorescent chem-nanosensing system to the analyses of Cur in the practical samples.More importantly,when the pH is decreased from 8.0 to 4.4,the N,S-CDs reveals an extraordinary emission escalation in the yellow fluorescence extent(?_em=543nm),and the pK_a value of the N,S-CDs was calculated as 6.06.Moreover,the N,S-CDs displays a good linear relationship with the physiological range of pH 5.0-7.4,which is meaningful for the research of near-neutral cytosolic pH.Ultimately,the laser scanning confocal microscopic images of intracellular distribution and the determination of pH in SiHa cells were successfully carried out,implying that the N,S-CDs possess excellent cell membrane permeability and are capable of being further applied to real-time pH fluctuations monitoring in live cells with negligible autofluorescence.Chapter 4:Less toxic elements nitrogen and sulfur co-doped carbon-based dots?NSCDs?have been prepared by microwave-assisted pyrolysis of citric acid and N-acetyl-L-cysteine as the carbon source and N,S-dopant,respectively.The structure and optical properties of NSCDs are characterized by transmission electron microscopy,X-ray photoelectron spectroscopy,elemental analysis,fourier transform infrared spectroscopy,UV-vis absorption,and photoluminescence spectroscopy.The mechanism for the formation of NSCDs is also discussed.The as-prepared NSCDs show small size distribution and excellent dispersibility.Their strong blue fluorescence(?_em=443 nm)is observed when the excitation wavelength is between 260 nm and 380 nm.Moreover,they exhibit high tolerance to various external conditions including external cations,pH values and continuous UV excitation.More strikingly,as the emission of NSCDs is efficiently quenched by Cr?VI?,the as-prepared NSCDs are employed as a highly sensitive and selective probe for Cr?VI?detection.The linear range is 0.5-125?M Cr?VI?with the detection limit of 20nM.The as-synthesized NSCDs have been successfully applied for Cr?VI?sensing and cellular imaging.Chapter 5:Chromium?VI?[Cr?VI?]is a harsh environmental contaminates and has been proved to be highly toxic,carcinogenic and mutagenic.Therefore,developing an inexpensive,good selective and highly sensitive nanoprobe for the detection of Cr?VI?is in urgent demand.In this work,an"on-off"fluorescence phosphorus/nitrogen dual-doped CDs?PNCDs?probe was developed for the determination of Cr?VI?based on inner filter effect?IFE?.The proposed PNCDs nanoprobe shows its distinct merits of simplicity,convenience,fast implementation,good selectivity and high sensitivity towards Cr?VI?,allowing its potential application in the determination of Cr?VI?in environment and biosystem.In addition,the chelation effect of the functional groups in reductant and Cr?VI?,and the easy-conversion of Cr?VI?to reduced states[i.e.Cr?III?and Cr?0?]by reductants makes the minimization of IFE with a concomitant recovery of PNCDs fluorescence possible.Hence,the PNCDs/Cr?VI?hybrid was used as an"off-on"fluorescence probe for sensing of ascorbic acid?AA?.For the detection of Cr?VI?,the linear range and the limit of detection achieved were 1.5-30?mol/L and 23 nmol/L,respectively.For the detection of AA,the linear range and the limit of detection obtained were 5.0-200?mol/L and 1.35?mol/L,respectively.More importangly,the probe enables dual function detection of Cr?VI?and AA in living cells.