Functional Modification Of Carbon Quantum Dots And Their Applications For Bioimaging And Biosensing

Carbon quantum dots(CDs)are the carbon nanomaterials with three-dimensional nano size,carbon as the basic structural units and rich in organic functional groups on the surface,and can be dispersed in water or other solvents with spherical shape.For their unique optical properties,wonderful water solubility,low cytotoxicity and good biocompatibility,they have been applied in biological imaging,sensors,photocatalysis,medicine,etc.In this paper,the fluorescent probes with specific responses to some metal ions were successfully constructed by modification the surface of the carbon quantum dots with decorations through designing different compounds.And their applications in cell imaging,biological sensor and the feasibility in detection of ions in actual samples were also studied.The main contents are as follows:(1)For EDTA being full of C and N actoms in its molecular and thiourea also containing N and S,which have been considered as necessary atoms to improve the fluorescence quantum yield of CDs.When the molar ratio of EDTA and thiourea was 1:2.5,synthetic temperature and heating time were 180 ?C and 10 hours,respectively,the obtained N,S-CDs owned good water solubility and monodispersity,the average particle size of about 2.5 nm,and high luminescence.No further modification,the fluorescence intensities of N,S-CDs were obviously quenched only by Hg2+ even at its fairly low concentrations.This means that a high selectivity and sensitivity of Hg2+ fluorescent probe has been built.Using the probe in detection of mercury ions in actual samples,the recovery rates of mercury were between 96.4% and 105.2%,which prove that the method is feasible and accurate,and can also detect Hg2+ in Escherichia coli.(2)The CDs were prepared by hydrothermal treatment taking EDTA as substrate and the surface of the prepared CDs were rich in-NH2,-OH and-COOH.Then the carbon quantum dots were modified by thiosemicarbazide as recognized molecule via amidation reaction at the esistence of EDC and NHS.The modified carbon quantum dots showed obvious wavelength dependence,the optimum excitation wavelength and emission wavelength were 370 nm and 450 nm,respectively.In addition,the fluorescence intensities changed little with the pH values increasing from 3 to 10.And the carbon quantum dots also had good stability in different concentrations of ionic solutions.The strongest fluorescence intensity was obtained in Tris-HAc buffer system.The carbon quantum dots had a specific selectivity to Cu2+.After being incubated with carbon quantum dots HeLa cells and Escherichia coli emitted bright blue and green fluorescence at 405 and 488 nm excitation walvelengths under laser scanning confocal microscope.While no fluorescence signals were observed in the cells without carbon quantum dots at the same conditions.These certified that the probe could easily cross the cell membrane and gathered in the cells.Following adding Cu2+,the fluorescence intensity dimmed,which implied that the carbon quantum dots could be used in multicolor bioimaging and biosensing.(3)4-butyl thiosemicarbazide was firstly gotten by the reaction of butyl isothiocyanate and hydrazine hydrate with anhydrous ethanol as solvent at room temperature.Then the Cu2+ nanosensor was successfully built by conjugating 4-butyl thiosemicarbazide as identifying molecule onto the surface of CDs via chemical reactions.The good linearities were also achieved with the concentrations of Cu2+ in the range of 0-0.10 ?? and 4-50 ??,respectively.The Stern-Volmer equations were F/F0 = 1.0005-0.6710 [Cu2+](R2 = 0.9994)and F/F0 = 0.6671-0.0947 [Cu2+](R2 = 0.9982)respectively and the detection limit was 5.05 nM.The fluorescent probe also showed high water solubility,low cytotoxicity,excellent biocompatibility and cell membrane permeability.Following the detection mechanism was also speculated and the method was applied in determination of Cu2+ in mineral water and human hair.(4)Functionalizing carbon quantum dots with 4-Naphthalenyl-3-thiosemicarbazide by chemical reaction.After functionalization the average particle size of carbon quantum dots was 3.1 nm which increased 0.7 nm than the original particle size(2.4 nm)manifesting that 4-Naphthalenyl-3-thiosemicarbazide had been modified on the surface of carbon quantum dots,joining the 4-Naphthalenyl-3-thiosemicarbazide on the surface of the carbon quantum dots increased the particle size.The conclusion was also proved by FT-IR and XPS results.Fe3+ could effectively quench the fluorescence intensity of the carbon quantum dots.This may be due to 4-Naphthalenyl-3-thiosemicarbazide playing an important role,the inner filter effect causing by the complexation between Fe3+ and 4-Naphthalenyl-3-thiosemicarbazide prompted the fluorescence quenching.Adding the carbon quantum dots into HeLa cells the fluorescence intensities were stronger in the cytoplasm than in the nuclei,which can provide the basis for carbon nanomaterials application in the cellular location.