Syntheses Of Novel Nitrogen-doped Carbon Dots For Highly Selective Detection Of Metal Ions And Cellular Imaging

As a new family of versatile nanomaterials,focus is given on carbon dots?CDs?due to its optical and physicochemical property,high-biocompatibility and low cost in the past ten years.CDs have been in the spotlight of tremendous potential applications,including optronics,biology,medicine and sensing issues.Compared with conventional semiconductor quantum dots?QDs?,which were comprised of heavy metals such as cadmium or lead,CDs are more environmental friendly in synthesis,they can be favourably consumed as alternatives in further developments of biological,environmental and food areas attributing to their low-toxicity compared with semiconductor quantum dots,water-soluble and high photostability.Herein,two types of novel CDs were synthesized by one-step hydrothermal synthetic method,and were employed in highly selectively detection of metal ions cellular imaging.Three chapters of this thesis contribute to the following research contents:Chapter 1: Classification and physicochemical properties of common carbon nanomaterials were introduced generally.Preparation procedures and sensing application of CDs were reviewed.Chapter 2: Strongly blue fluorescent nitrogen-doped carbon dots?CDs?were synthesized by using citric acid as the carbon source and diethylenetriamine?DETA?as the nitrogen source according a one-step hydrothermal method.Several synthetic parameters,including the molar ratios of initial starting materials,the temperature and time of hydrothermal reaction,were investigated and optimized.The range and average value of the diameters of the resultant CDs were 1.2-4.0 nm and 2.3 nm,respectively.The synthesized CDs display fluorescence with excitation/emission maxima of 391/438 nm and a quantum yield of 58%.Fluorescence of the synthesized CDs can be quenched by Co²⁺ ions,and this effect was exploited to design a method for determination of Co²⁺ in water and to image it in living He La?cervical carcinoma?cells.The limit of detection and linear range of Co²⁺ using the synthesized CDs as fluorescence probe were 0.4 ?mol?L^-1 and 0-90 ?mol?L^-1,respectively.Due to the selective and sensitive response of Co²⁺,the synthesized CDs possess potential applications in biological labeling for the demands such as monitoring the distribution of Vitamin B-12 or other medicines containing cobalt in cells or organisms.Chapter 3: A water-soluble,low-toxicity fluorescence sensor was constructed based on hydrothermal synthesis of CDs,?-cyclodextrin as the carbon source and diethylenetriamine?DETA?as the nitrogen source.Surface of the CDs was modified by ascorbic acid to immobilize amide functional groups.Several synthesis conditions of the CDs,including synthesis time and temperature,and molar ratio of reactants,were optimized.The optimal excitation/emission wavelengths of CDs are 338/415 nm,and the fluorescence quantum yield is 1.9%.Fluorescence of the CDs can be quenched by Hg²⁺ ions,therefore a fluorescence probe for determination of Hg²⁺ in water was developed by using the CDs.The limit of detection and linear range of Hg²⁺ obtained by using the developed probe were 0.07 ?mol·L^-1 and 0.2-2 ?mol·L^-1,respectively.Imaging of distribution of Hg²⁺ in and around living BEL-7402 cells was also performed by using the developed probe.