Preparation Of Carbon Quantum Dots And Its Application In Fiber Optic Cholesterol Sensor

Cholesterol is a representative health indicator in human body.It mainly comes from daily diet and plays an important role in constructing cell membrane and cell structure,and maintaining normal cell activities.It has a high concentration in the liver,spleen,kidney and skin.It is one of the most important biomarkers for cardiovascular disease and hypertension.When the concentration of cholesterol is too low,it will cause anemia and reduce resistance.While the cholesterol concentration is too high,it can cause obesity and increase the risk of cardiovascular disease,and endanger human health.Therefore,it has an important significance to detect and control the concentration of cholesterol in the normal range of disease prevention and human health.Biosensors based on nanomaterials(such as gold nanoparticles,graphene oxide,etc.)are a combination of multiple disciplines,which can not only significantly improve the sensitivity and specificity of biological detection,but also detect and control atoms or molecules,promising applications in biological detection and other fields.Carbon quantum dots(CQDs)are a novel nanomaterial with fluorescence characteristics,which have many advantages such as photoluminescence,easy surface modification,abundant precursors and harmonious compatibility with biomolecules.They have been widely used in the biomedical field.In this thesis,CQDs and cholesterol oxidase(COD)were combined to prepare CQDs-COD fluorescence probe,which can detect cholesterol specifically.Based on this mechanic,a new fiber optic cholesterol sensor was prepared.It has realized real-time detection of cholesterol in a large concentration range.In addition,gold nanorods(Au NRs)were combined with CQDs to prepare a double mode cholesterol probe based on the fluorescence method and colorimetry.The double signal detection mode can avoid the influence of interference factors.The main research contents and results are as follows:(1)Blue luminescent CQDs were synthesized from citric acid and cysteine by microwave method,and its surface morphology,microstructure and optical properties were studied.CQDs-COD fluorescent probe was prepared by chemical cross-linking of CQDs and COD,the optimal cross-linking conditions of CQDs-COD complex were studied.The specific detection of cholesterol was carried out used CQDs-COD complex,and the fluorescence spectrum corresponding to the different concentrations of cholesterol was obtained.The corresponding standard curve and linear correlation coefficients were obtained by fitting the Stern-Volumer equation.The cytotoxicity of CQDs-COD complex was verified by the CCK-8 method.(2)CQDs-COD/CA composite sensitive membrane was prepared by the embedding method,and the effects of preparation parameters(such as the amount of fluorescence indicator,film forming conditions and coating process parameters,etc.)on its fluorescence characteristics were detailed.A cholesterol sensor was obtained by fixing the composite sensitive film on the end face of 600 μm quartz fiber by lifting plating method,and a new type of optical fiber cholesterol sensor detection platform was built.The optical cholesterol sensor has good selectivity for cholesterol,which can detect the concentration of cholesterol in the range of 2-6 m M and 1-100 μM,and the corresponding standard curve is also obtained.(3)Au NRs were prepared by the seed growth method.The length and width of single gold nanorods were about 70 nm and 20 nm,respectively,and the average aspect ratio of Au NRs was about 3.344.Au NRs-CQDs complex was formed by connecting Au NRs with CQDs through the Au-S bond.The structure and optical properties of Au NRs-CQDs complex were characterized by TEM,FT-IR and UV absorption spectrum.The optimal binding conditions of Au NRs-CQDs complex were studied.COD was immobilized with Au NRs-CQDs complex by the chemical crosslinking method,and characterized by FT-IR and UV-Vis,which proved the immobilization and formation of the complex system.Then,Au NRs-CQDs-COD complex was used as a dual-mode sensing probe to detect cholesterol solution in the concentration range of 0.1-1 m M by dual signals.Two standard curves corresponding to the colorimetric method and fluorescence method were obtained respectively.