| Carbon dots(CDs)are a new type of fluorescent nanomaterials.Because of their good biocompatibility,excellent fluorescence properties,cheap synthetic materials and convenient synthesis methods,CDs have excellent application prospects in bioimaging,detection,molecular biology and other fields.Although some progress has been made in the synthesis and application of carbon dots,there are still some theoretical and experimental problems to be solved urgently.For example,How to synthesize carbon dots with higher quantum yield or multi-color from green materials to meet the requirements of multimodal and multifunctional applications in the fields of biomarkers,chemical sensing,nanomaterials diagnosis and treatment.In this paper,the definition,preparation,properties,applications and characterization of carbon dots are introduced in the introduction.Then,our research work is carried out from the following four aspects:1.Using egg white powder as carbon source,a new type of nitrogen,oxygen and phosphorus doped carbon dots(N,O,P-CDs)were prepared by hydrothermal treatment.The optimum preparation conditions were obtained by optimizing reaction temperature,time and dosage.TEM,AFM,XPS,Raman and fluorescence spectrophotometer were used to characterize the structure,optical properties and elemental composition of the carbon spots purified from ethanol.The data show that the particle size of CDs was about 3 nm,and the lattice spacing was 0.21 nm.Spectroscopic data show that the fluorescence of N,O,P-CDs was located in the blue band,and the absorption peak was 310 nm.The maximum emission wavelength of fluorescence will shift to red with the increase of excitation wavelength.The fluorescence intensity increased to 105% after storaged for 80 days.At the same time,under the interference of 1 M salt ion concentration,the fluorescence intensity did not change,indicating that the carbon dots had good stability.Cell imaging showed that N,O and P-CDs could mark cells well.Compared with undoped CDs,the graphitization degree of N,O,P-CDs increased,the number of surface amino carboxylic phosphoric acid groups increased,and the quantum yield of CDs increased from 6.7% to 11.2% with the change of structure and surface functional groups.The increase of hydrophilic groups improved the water solubility of carbon spots and the application in labeling and detection.2.Immunofluorescence probes of N,O,P-CDs were prepared by coupling the prepared N,O,P-CDs with ovalbumin(OVA)antibody.Based on the interaction of fluorescence resonance energy transfer(FRET)between N,O,P-CDs and graphene oxide(GO),a rapid and sensitive method for the detection of ovalbumin(OVA)was established.Under the optimum conditions,the linear range of quantitative detection of OVA was 0.5-15 ug/mL,and the minimum detection limit was 0.153 ug/mL.It has the advantages of high efficiency,speed and sensitivity.The test results of synthetic samples and actual samples show that the established method could be applied to practical detection.3.The panchromatic CDs was synthesized from gallic acid and o-phenyl two amine as raw materials and ethanol as solvent.Blue,green,yellow and red CDs were obtained by silica gel column chromatography.Carbon structure,optical properties and element composition were characterized by TEM,AFM,XPS,Raman and fluorescence spectrophotometer.Structural data show that the size and thickness of the four CDs distributed in 2-3 nm,and their shapes were nearly spherical.The size of the four CDs did not change with the fluorescence red shift,and the degree of graphitization decreased gradually.Spectroscopic data show that the emission of CDs was related to the transition of C=C bond and the n-?* transition of C=N bond and C=O bond.The absorption peak at 300-500 nm shows a red shift trend.The maximum emission wavelengths were 463,524,555 and 604 nm,respectively.They did not have excitation wavelength dependence and contain multiple fluorescence emission centers.The quantum yields of the four CDs were 11.2%,7.8% 10.5% and 3.3% respectively.Elemental analysis of CDs shows that CDs were composed of C,N and O.The fluorescence of CDs was controled by surface groups such as C = N,C = O and-COOH.No cytotoxicity was observed when the CDs content was less than 50 ?g/mL.The fluorescence intensity was maintained above 80% when irradiated by 100 W ultraviolet lamp for 100 min.Under the interference of 2 M NaCl,the fluorescence intensity remained above 90%,indicating that CDs had good stability.4.Graphene quantum dots(GQDs)with blue,green,yellow and orange colours were synthesized by using potassium hydrogen phthalate,phenylenediamine and potassium periodate as raw materials and water as solvent.Silica gel column chromatography was used to separate and purify the GQDs.The structure,optical properties and element composition of GQDs were characterized by TEM,AFM,XPS,Raman and fluorescence spectrophotometer.Structural data show that the particle size of GQDs increased with the red shift of emission wavelength.The thickness of GQDs was 1-2 nm.The ratio of D-band to G-band was less than 0.3.It has a very high degree of graphitization and its luminescence is controlled by quantum confinement effect.Spectral data show that the ? = ?* transition of C = C bond and the n-?* transition of C = N bond and C = O bond are related.The maximum emission wavelengths were 420 nm,500 nm,540 nm and 555 nm,and the quantum yields were 9.7%,8.8%,9.3%,10.3% respectively,with multiple fluorescence centers.Elemental analysis of GQDs shows that GQDs is composed of C,N and O elements.No cytotoxicity was observed when the four GQDs content was less than 50 g/mL.The fluorescence intensity was maintained above 80% when irradiated by 100 W ultraviolet lamp for 100 min.Under the interference of 2 M NaCl,the fluorescence intensity remained above 90%,indicating that CDs had good stability. |
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