Studies On The Synthesis Of Functional Graphene, Graphene Quantum Dots And Their Properties

The traditional resonance energy transfer can effectively occur only when the distance between energy donor and acceptor is less than10nm, which greatly limit its application in biochemical analysis. As a result of special physical and chemical properties, graphene has been widely used in the microelectronics, functional materials and chemical sensing fields since it was discovered by Geim in2004. And the existing theoretical research suggests that if graphene is applied in the energy transfer system, the resonance energy transfer remains when the distance between donor and acceptor run up to30nm. Graphene quantum dots, as a new kind of quantum dots, have potential applications in nanodevices, biological medicine, and sensors etc, owing to their stable photoluminescence, low cytotoxicity, excellent solubility and chemical inertia properties. They can be used in the energy transfer system as an energy acceptor. However, there are little reports about using graphene as energy donor or graphene quantum dots as energy acceptor. In this paper, we built new methods to prepare functional graphene and graphene quantum dots, investigated the ability of graphene used as energy donor or graphene quantum dots as energy acceptor, and further explored their application in biochemical analysis. The main contents are listed as follows:1. The preparation of gallic acid-modified graphene (GA-RGO) was implemented using graphene oxide (GO) as precursor and gallic acid as reductant and stabilizer. Ultraviolet-visible absorption spectroscopy. Fourier transform infrared spectrum (FT1R). Raman spectroscopy. scanning electron microscope (SEM), X-ray powder diffraction (XRD) were conducted to characterize the as-prepared GA-RGO. The results demonstrate that the graphene oxide has been reduced by gallic acid. Moreover, the interaction of GA-RGO and different organic dyes was investigated. On one hand, the results indicate that the GA-RGO can efficiently quench the fluorescence of cationic dyes, and the quenching efficiency is higher than GO and hydrazine-RGO in the same condition. This implies that the GA-RGO can be used as energy acceptor in the long range resonance energy transfer system with its high quenching efficiency. On the other hand, the GA-RGO can enhance the fluorescence of the fluorescein anionic dyes while the GO and hydrazine-RGO quenches it. This phenomenon has never been reported, and it is significant for the application of graphene in photoelectric sensing and biochemical analysis.2. Synthesis of graphene quantum dots and their cell chemical analysis. A simple and efficient approach to prepare graphene quantum dots (GQDs) has been developed by calcining the mixture of fullerenes and solid sodium hydroxide at300℃for4h. The obtained GQDs have stable fluorescence properties, excellent solubility and good biocompatibility. The GQDs was structurally and compositionally characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), FTIR, and Raman spectroscopy. It was found that the as-prepared GQDs are spherical dots and their diameters are in the range of2-3nm with a narrow size distribution. The results of high resolution transmission electron microscopy (HRTEM) reveal that the GQDs have high crystallinity structure, and the lattice parameter is0.24nm. The XPS and FTIR results imply the existence of hydroxyl and carboxyl on the surface of the GQDs. The GQDs have excellent blue photoluminescence properties with quantum yield of4.82%. The fluorescence of GQDs was both excitation-dependent and pH-dependent. In addition, the GQDs had been successfully applied for highly selectively intracellular sensing and imaging of iron ions based on its low cytotoxicity, good biocompatibility and the fluorescence quenching due to the aggregation of the GQDs for the interactions between metal ions and hydroxyl or carboxyl on the surface of the GQDs.Generally, in this paper, we found the efficiency of energy transfer when reduced graphene oxide used as energy acceptor was higher than graphene oxide as energy acceptor. This is an advantageous supplement to the applications of graphene in biochemical analysis. The higher sensitivity will be obtained when reduced graphene oxide replace graphene oxide as as energy acceptor. The way we developed to prepare graphene quantum dots from fullerene is simple, facile and effective. The graphene quantum dots have more stable fluorescence and better biocompatibility compared to the traditional organic dyes and quantum dots. It can be effectively used in biochemical analysis as an energy donor or fluorescence probe.In a word, we have extended the method to prepare the energy donor and acceptor in energy transfer. These methods proposed herein are all simple, quick and effective. We hope these will be benefit for further development of the application of long-range resonance energy transfer in biochemical analysis.