Preparation,Property And Application Of Nitrogen Doped Positive Carbon Quantum Dots In The Detection Of Urea And Chondroitin Sulfate

The carbon quantum dots(CQDs)with fluorescent properties can be applied in the fields such as bio-detection and drug controlled-release carrier.On this basis,the strategies of the further functional improvement of CQDs,such as doping with appropriate elements,will changs the electronic structure as well as optical properties of CQDs and further expand the application of CQDs in biological probes and catalysis,which has turned into a research hotspot.In this paper,a CQD with specific modification,giving pH-sensitive response and interacting with biomolecules is established to achieve the determination of some bioactive components.This topic prepared a new kind of nitrogen-doped CQD(N-CQDs)with the characterization of its properties and the exploration of application in life analysis:Chapter 1 Preparation and Properties of N-CQDsIn this chapter,a new kind nitrogen-doped CQD was fabricated.By means of UV-Vis absorption spectroscopy,Fourier transform infrared spectroscopy,transmission electron microscopy,zeta potential and photoelectron spectroscopy,the morphology,structure and properties of this N-CQDs were characterized.Meanwhile,the stability and biocompatibility of N-CQDs in different environmental conditions were tested,and the response of N-CQDs to external factors was investigated..The results illustrated that N-CQDs possessed surfacial positive charge,good biocompatibility,superior stability in different concentrations of salt solution,and excellent photobleaching resistance.Furthermore,N-CQDs responsed selectively to pH and metal ions especially to copper ions.Chapter 2 Application of N-CQDs in the Determination of UreaIn this chapter,a fluorescence method for urea detection was developed based on the pH-sensitive response of N-CQDs.The pH of the tested solution can be changed according to the urease-catalyzed urea reaction.In this way,the relationship between different concentrations of urea and fluorescence intensity of N-CQDs was measured.Furthermore,the possible influence of common interferences on urea detection was also investigated.The comparison of this detection method with present clinical trials showed that this fluorescence method can be adopted to detect the concentration of urea in complex systems.Moreover,this method suggested good accuracy and reproducibility for urea detection.Chapter 3 Application of N-CQDs-ssDNA Interaction System in Determination of Chondroitin SulfateIn this chapter,based on the interaction between N-CQDs and FAM-DNA,another kind of N-doped positively charged carbon quantum dots(N-CQDs)was designed.Then,a system based on the interaction between N-CQDs and FAM-DNA was developed for the detection of chondroitin sulfate.As an adsorption platform,N-CQDs reacted with FAM-DNA in a certain buffer with fixed concentration and pH to form an FAM-DNA acting system with FAM fluorescence quenching but stable fluorescence of N-CQDs.The electrostatic interaction between negatively charged chondroitin sulfate and N-CQDs displaced FAM-DNA from the FAM-DNA system and recover the fluorescence of FAM-DNA.The degree of FAM-DNA fluorescence recovery was closely related to the concentration of chondroitin sulfate.Thus a method for determining chondroitin sulfate based on the change of the fluorescence signal of FAM-DNA was built.This established method is practical and can be accurately applied to detect the contents of chondroitin in medicines and joint fluids.