Preparation And Application Of Heteroatom Doped Carbon Dots With Tunable Luminescence Properties

Carbon dots have become a type of most popular fluorescent nanomaterials due to their outstanding biocompatibility,excellent water-solubility,remarkable photobleaching resistance and multicolor fluorescence emission,and thus have been widely used in various fields.Although the carbon dots have made great progress after more than ten years of development,there are still some problems that have not been solved,mainly in the following aspects:（1）Based on the excellent properties of carbon dots,the application fields of carbon dots are becoming wider and wider.However,the controllable preparation of particle size and morphology and the tunable fluorescence restrict its further development.（2）At present,the understanding of heteroatom doped carbon dots is not profound enough.How to control the doping atoms and doping amount to get desired carbon dots is still a problem.（3）Moreover,up to now,the fluorescence mechanism of carbon dots has not been fully studied.In view of the above research status,a series of fluorescence-tunable heteroatom doped carbon dots were designed and prepared with different dopants,and their properties were also explored.The possible luminescence mechanism was inferred by analyzing the carbon dot characterization results.The main contents are as follows:1.Nitrogen-doped carbon dots were prepared using a simple hydrothermal method with fructose and urea as precursors.The as-prepared carbon dots have good water-solubility,and the fluorescence of their aqueous solution gradually blue-shift as the concentration decreases.The carbon dots also have excellent stability and thus can be used as a fluorescent probe to detect Hg²⁺ion.The detection limit is 1.26μM.2.Fructose,urea and boric acid were pyrolyzed using one-step method to prepare boron and nitrogen co-doped carbon dots with tunable luminescence.As the content of urea increases,the fluorescence emission peak gradually is blue-shifted.The phenomenon can be attributed to the surface state emission mechanism caused by surface defects of the carbon dots.The as-prepared carbon dots maintain considerable stability at high salt concentrations and long exposures（UV lamps）,and have a concentration-dependent fluorescence emission behavior.The carbon dots also have low toxicity and good biocompatibility,and were successfully used in the fields of ion detection and biological imaging.3.Sulphur and nitrogen co-doped carbon dots with tunable fluorescence were prepared using hydrothermal method,with citric acid,tris（hydroxymethyl）aminomethane,and potassium persulfate as precursors.As the reaction temperature increases,the maximum emission wavelength of the as-prepared carbon dots gradually shifts to long wavelengths.Meanwhile,the solid state quantum yield of the carbon dots is as high as 34.44%.In addition,the carbon dots can be used as a chemical sensor to detect Hg²⁺ion.The detection limit is 0.67μM.The application of carbon dots in cell imaging has low toxicity and good biocompatibility.