Research On Application Of Nitrogen-doped Graphene Quantum Dots In Environmental And Biological Sample Analysis

The detection of curcumin(Cur),phytic acid(PA),and 2-Mercaptobenzothiazole(MBT)is great significance in environmental and biological sample analysis.Graphene quantum dots(GQDs)are a novel zero-dimensional(0D)carbon nanomaterial,which has strong photoluminescence,low toxicity to cells,good biocompatibility and water solubility.So it is widely used in the analysis and detection of toxic substances in environmental and biological samples.Studies had shown that heteroatom doping can adjust the intrinsic properties of GQDs effectively.Nitrogen-doped graphene quantum dots(N-GQDs)can effectively adjust the electronic,surface and local chemical properties to improve the sensitivity and selectivity of target compounds.In this thesis,citric acid and urea were used as raw materials.N-GQDs were prepared by one-step hydrothermal synthesis method,and their morphology and optical properties were characterized.Based on their characteristics,several new fluorescent sensors based on N-GQDs were constructed for the detection of Cur,PA and MBT in environmental water samples and biological samples,the results were satisfactory.The specific research content as follows:1.A new type of fluorescence sensor was constructed to realize quantitative detection of Cur in water and urine samples.N-GQDs were prepared by one-step hydrothermal synthesis using urea as the nitrogen source and citric acid as the carbon source.Fourier transform infrared spectrometer(FTIR),X-ray diffractomer(XRD),X-ray photoelectron spectroscopy(XPS),Raman spectrometer,transmission electron microscope(TEM),fluorescence spectroscopy,and ultraviolet-visible absorption(UV-vis)spectra were used to characterize the synthesized N-GQDs.The results showed that we had synthesized N-GQDs successfully,which were rich in carboxyl,hydroxyl and amino groups on the surface,uniform particle size and uniform distribution.Cur has a wide absorption band.Both the excitation and emission spectra of N-GQDs overlap with the absorption band of Cur,which can produce an internal filtering effect.Cur can quench the fluorescence of N-GQDs significantly.Based on this,The new fluorescence sensor of N-GQDs was used for the detection of Cur.Cur had a good linear relationship in the concentration range of 0.1-9?mol L^-1 and 10-50?mol L^-1 respectively.The detection of limit(3?/k)is 75.6 nmol L^-1.The method was applied to the determination of Cur in water samples and urine samples successfully,and the spiked recovery was 97.0%-104%.The results were satisfactory.2.A new type of fluorescence sensor was constructed to realize quantitative detection of PA in urine samples.The fluorescence of N-GQDs was significantly quenched with Fe³⁺due to photoelectron transfer(PET)with hydroxyl and carboxyl groups on the surface of N-GQDs.When PA was added to the N-GQDs/Fe³⁺system,PA complexes with Fe³⁺,so that Fe³⁺was released from the surface of N-GQDs,and the fluorescence of quantum dots was restored.Based on this,a new method based on N-GQDs/Fe³⁺system for detecting PA was constructed.Under the optimized experimental conditions,the linear range of PA was 0.2-2.5?mol L^-1,the detection of limit(3?/k)was 60 nmol L^-1.The system was applied to the detection of PA in urine samples successfully.The spiked recovery was 95.0%-103%with satisfactory results.3.A new type of fluorescence sensor was constructed to realize quantitative detection of MBT in water samples.Cu²⁺can combine with specific functional groups on the surface of the quantum dots to form N-GQDs/Cu²⁺complex,which quenches the fluorescence of the quantum dots.When MBT was added,Cu²⁺has a strong interaction with the thiol groups on the surface of MBT,which caused Cu²⁺to dissociate from the surface of N-GQDs and fluorescence recovered quickly.Based on this,a new method for was constructed to detect MBT quickly in actual samples.Under optimized experimental conditions,MBT showed a good linear relationship in the range of 0.4-40?mol L^-1,the detection of limit(3?/k)was 0.1?mol L^-1.This method can be applied to the detection of MBT in actual water samples successfully.The spiked recovery was 95.0%-101%with satisfactory results.