Preparation Of Dual Emitting Carbon Dots And Their Application In Cell Differentiation And Fluorescence Sensing

Carbon dots（CDs）are a kind of carbon-based zero-dimensional nanomaterials discovered in 2004.Their three-dimensional dimensions are all between 0-10 nm.CDs are generally composed of spherical cores formed by orderly or disorderly stacking of multiple hybrid carbon and rich functional groups distributed on the surface of spherical cores.Because of their good biocompatibility,low cytotoxicity,high quantum yield and so on,CDs have been widely used in biochemical sensing,fluorescence diagnosis,photocatalysis and other fields.In this thesis,CDs with double fluorescence emission peaks were synthesized quickly and conveniently by one-step solvothermal method,and the effects of surface functional groups and solvents on the fluorescence of double fluorescence emission peaks were investigated,and the application to the detection of water in ethanol,the detection of iron ions,cell imaging and visual recognition of cancer cell were also studied.The main research contents of this thesis are as follows:（1）CDs with single particle size were obtained by one-step solvothermal method,filtration and dialysis purification by using phenylalanine and 1,5-diaminoanthraquinone as raw materials and ethanol as solvent.CDs had peculiar phenomena of the double fluorescence emission peaks（363 nm,563 nm）.One emission peak was excitation dependent,while the other was not excitation dependent.Studies had shown that the functional groups（amino and carboxyl）on the surface of CDs had a significant impact on the fluorescence properties of CDs.When the amino or carboxyl groups on the surface of CDs were removed by adding NHS and EDC or hydrazine hydrate respectively,the intensities of both fluorescence emission peaks of CDs decreased as the amino or carboxyl group number decreased.The first emission peak was more affected by amino and carboxyl groups than the second emission peak.The fluorescence intensity ratio of the second emission peak（I₂=563 nm）to the first emission peak（I₁=363 nm）had a good linear relationship with the added NHS and EDC or hydrazine hydrate.The fluorescence performance of CDs had a solvent effect,and the second emission peak shifted from 535nm to 580 nm as the polarity of the solvent increased,which further indicated that the fluorescence emission mechanism of CDs was surface state photoluminescence,and the interaction between the solvent and defects on the surface of CDs caused changes in the fluorescence emission peak.On this basis,a method using dual fluorescence emission peak intensity of CDs as ratio probes to detect water content in ethanol was developed.The intensity ratio of the two emission peaks was positively correlated with the water content in ethanol.The detection linearity is good and has good application in water detection.This method had good detection linearity and would have good application in water detection.（2）Three types of phenylalanine-binding CDs were prepared by one-step solvothermal method using phenylalanine,citric acid,and anthraquinone（1-aminoanthraquinone,1,5-diaminoanthraquinone）as the main raw materials and ethanol as a solvent.The effects of quantity of amino groups in anthraquinone on CDs were investigated.It was found that the CDs prepared by the reaction of anthraquinone without amino groups with phenylalanine had only one blue fluorescence emission peak,while the CDs prepared from 1-aminoanthraquinone and 1,5-diaminoanthraquinone had two fluorescence emission peaks.In addition,the CDs prepared with 1,5-diaminoanthraquinone as raw material had good biocompatibility and could be transported into cancer cells through a large number of amino acid transporters on the surface of cancer cells,while normal cells had only a small amount of CDs through endocytosis,which laid a foundation for distinguishing cancer cells from normal cells.Similarly,the difference in the number of amino groups in anthraquinone also affected the number of binding between CDs and phenylalanine.The smaller the number of amino groups in the precursor,the less phenylalanine on the surface of CDs and the less CDs transported into cells through amino acid transporters on the surface of cancer cells and thus the weaker the fluorescence in MCF-7 cells observed under the laser confocal microscope.In conclusion,the prepared CDs had unique fluorescence properties and have application value in cell imaging and fluorescence visual recognition of cancer cells.（3）Carbon dots with dual emission fluorescence were prepared by carbonizing rhodamine and phenylalanine using a one-step hydrothermal method.One fluorescence emission peak was excitation wavelength dependent,while the other fluorescence emission peak was not.The prepared CDs had uniform spherical shape,good dispersion and excellent water solubility.They could be used for the specific detection of Fe³⁺ions in aqueous solution,with a detection limit of 1.1μM and good anti-interference ability,because Fe³⁺ions were easier to combine with the hydroxyl groups on the surface of CDs to form aggregates（such as iron hydroxide）than other metal ions,resulting in the fluorescence quenching of CDs.Fe³⁺ions not only quenched the fluorescence intensity of two double emission peaks of CDs,but also changed the relative fluorescence intensity of these two emission peaks.Therefore,two different fluorescence analysis methods were used to specifically identify iron ions,and the results were consistent with each other.At the same time,double-emission fluorescent CDs had low hemolysis rate and cytotoxicity,indicating that CDs had little damage to cells,and were further used to detect Fe³⁺ions in cells.The above results showed that the prepared CDs would have potential application in detecting iron ions in blood and cells.