| Graphene quantum dots not only show small size features and good fluorescence property like conventional semiconductor quantum dots as a novel carbon nanomaterial, but also have advantages of low biotoxicity, chemical inertness and stable photoluminescence.Therefore, GQDs, attracted great interests from people, are ideal substitute for conventional semiconductor quantum dots in bioimaging,and makes great contributions to the detection and application of fluorescence sensors. Heteroatom doping is an important and effective approach to study and tune the material property, and have been widely applied in the preparation of new type of carbon nanomaterials. This thesis is to develop a fluorescence approach used for detection of iron ion and alkaline phosphate based on the fluorescence properties of graphene quantum dots in environmental conservation, early diagnosis of diseases providing a quick, sensitive, accurate and efficient method. The main results are as follows:1. Using a facile electrolyzing method to synthesize boron-doped graphene quantum dots (BGQDs). The BGQDs were produced by oxidizing graphite in an aqueous borax solution; then, the borate solution was filtered with BGQDs, and the borate was dialyzed from the filtrate, leaving a solution of BGQDs in water. The amount of the B in the BGQDs can be adjusted by changing the concentration of borax used for the electrolyte. The excitation wavelength- and B amount-dependent fluorescence characteristics of BQGDs were studied.2. Using the BGQDs as a fluorescent probe to determine Fe3+ ion levels in water samples. The fluorescence intensity of the BGQDs is measurable in real time, and its quenching is very sensitive to the concentration of Fe3+ ions in the system but not to other possible coexisting metal ions. The fluorescence quenching mechanism of Fe3+ ions to BGQDs is studied and explained based on spectrographic analysis and DFT simulations. The analytical signal, which is defined as F0/F, where F0 and F are the fluorescence intensities of the BGQDs before and after interaction with Fe3+ ions, respectively, displays a good linear relationship in the Fe3+ ion concentratio1 range of 0.01-100 ?m with a correlation coefficient of 0.999 and a limit of detection (LOD) of?(0.005±0.001)?mol/L. The LOD value is much lower than the water quality standards for Fe3+ ions (0.3 ppm, -5.36?m) in drinking water suggested by the WHO (World Health Organization) and EPA (U.S. Environmental Protection Agency),implying that this method has great potential for applications in real sample assays. For example, the determination of the Fe3+ ion levels in three water samples(tap water,groundwater,and lake water) gives approximately the same results as those determined by the EPA-recommended AAS (atomic adsorption spectroscopy) method.3. This thesis reports a convenient and real-time assay of alkaline phosphatase (ALP)level in living cells based on a fluorescence quench-recovery process at a physiological pH using the boron-doped graphene quantum dots (BGQDs) as fluorophore. The fluorescence of BGQDs is found to be effectively quenched by Ce3+ ions because of the coordination of Ce3+ ions with the carboxyl group of BGQDs. Upon addition of adenosine triphosphate (ATP)into the system, the quenched fluorescence can be recovered by the ALP-positive expressed cells (such as MCF-7 cells) due to the removal of Ce3+ ions from BGQDs surface by phosphate ions, which are generated from ATP under catalytic hydrolysis of ALP that expressed in cells. The extent of fluorescence signal recovery depends on the level of ALP in cells, which establishes the basis of ALP assay in living cells. This method has the ability of avoiding false signals arising due to the nonspecific adsorption of non-target proteins and can be extended to other enzyme systems, such as ATP-related kinases. |
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