Synthesis And Application In Analytical Detection Of Colorful Fluorescent Carbon Quantum Dots

Carbon quantum dots(QDs)are excellent fluorescent materials,which have attracted much attention since their discovery in 2004.Carbon dots with a variety of synthetic methods are widely used in various fields,but there are still many challenges.At present,there is no effective method to control the emission color of carbon dots.Most of the carbon dots are blue-green emission,limiting the application of carbon dots in biomedical fields.In this paper,we use p-phenylenediamine,3-aminopropyl triethoxysilane,citric acid and other raw materials to synthesize fluorescent carbon dots with different colors and functions by adjusting reaction conditions.The luminescence mechanism and application of the carbon dots are studied.The following results are obtained:1.By using the p-phenylenediamine as carbon source and adjusting the acidity of the reaction system,the precise control of the fluorescence color of the products can be achieved.The mechanism of luminescence is proposed and verified by experiments.The emission wavelengths of different fluorescent carbon dots cover the ranges from blue to red.The acid-controlling theory of the fluorescence is put forward through the in-depth study of the luminescence mechanism,which provides an important theoretical and practical reference for realizing the regulation of the fluorescent color of carbon dots.Through analyzing the structures of carbon dots with different emissions,it is found that the doping of N element in carbon dots has an important influence on the fluorescence of carbon dots.At the same time,the way that H~+affects the doping of N element in the product structure and influecnes the fluorescence of carbon dots further is explained.In the analysis of the fluorescent properties of different products,it is found that the fluorescence of yellow carbon dots(yCDs)has unique solvent-dependence and acidity-dependence.These properties are similar to those of some fluorescent organic compounds with donor(D)-receptor(A)structure.The assumption that the similar structures exist in carbon dots is presented.The results supporting this assumption are detected in the subsequent experiments.In addition,the concentration-dependence of the fluorescence of the carbon dots in ethanol is explained,and the aggregation-induced red shift of yCDs are confirmed.2.Silicon and nitrogen co-doped fluorescent carbon dots are synthesized from 3-aminopropyl triethoxysilane and their application in metal ion detection are studied.The quantum yield of the co-doped carbon dots is 29.7%.The fluorescence of the carbon dots shows good stability in the range of pH 3~13.The carbon dots can interact with trivalent iron ions specifically and the fluorescent intensities of the carbon dots have a good linear relationship with the concentration of iron ions in the range of 0~200?M.The co-doped carbon dots can be applied to detect the serum iron in clinic successfully and the results are in good agreement with the clinical results using gold standard test.3.A multi-nanomaterial system combined with fluorescent carbon dots are designed for the rapid and highly sensitive detection of the pathogenic bacteria.Sodium citrate is used as the raw material to synthesize stable carbon dots with a high fluorescent yield.The ratiometric fluorescent readout system consisted of the carbon dots and CdTe quantum dots responding to copper ions was realized.Copper nanoparticles are labelled on the antibodies to the bacteria.After the interaction between the antibodies and the bacteria,the copper nanoparticles are attached on the bacteria.After the copper ions releasing by the acid,the concentration of the bacteria can be detected by the amount of copper ions indirectly.Because a copper nanoparticle contains tens of thousands of copper ions,this step can amplify the signal and achieve the detection of the bacteria with a minimum of 10~3 CFU/mL.We hope to provide a feasible method for pathogenic bacteria detection without the culture in clinical samples.In summary,we have synthesized multi-color fluorescent carbon quantum dots successfully and studied their luminescence mechanism.Furthermore,we apply the carbon quantum dots in the metal ion detection and the highly sensitive pathogenic bacteria detection.Our work provides a reference for the fluorescence-controlled synthesis of carbon dots and their application in the field of the analysis and detection.