Synthesis And Analytic Application Of Graphene Quantum Dots With High Quantum Yield

Fluorescent carbon quantum dots(CQDs) are a new class of carbon nanomaterials, first obtained during purification of single-walled carbon nanotubes through preparative electrophoresis in 2004. CQDs have gradually become a rising star in the nanocarbon family, due to their benign, abundant and inexpensive nature. In striking contrast to semiconductor quantum dots and organic dyes, CQDs are superior fluorescent nanomaterials with good water solubility, suitability for subsequent functionalization, resistance to photobleaching, low toxicity, better biocompatibility, and low environmental hazard. So, CQDs are an attractive alternative for applications in the reseach of biology and biomedicine. Impressive as it is, the properties of the CQDs on multicolor fluorescence(FL) and quantum yields(QYs), however, pale in comparison to traditional metal-based semiconductor nanocrystals. In most cases, CQDs present simple blue fluorescence(the wavelength of the maxium emission is less than 500 nm) and QYs less than 10%, limiting the range of their practical applications. It is urgent to prepare high quality CQDs emitting near-infrared fluorescence with high QYs by facile strategy without tedious separation and purification process or surface passivation.This dissertation comprises mainly two aspects: the preparation and appilication of CQDs. First, by improving the oxidation ways of carbon source and experimental condition, a method of rapid deep oxidation of different carbon sources has been studied. Through concentrated nitric acid oxidation within 2-3 hours, two kinds of graphene quantum dots(GQDs, one type of CQDs) have been obtained successfully: green emitting GQDs(the wavelength of the maxium emission locates at 538 nm with a QY of 50%), and another kind of red emitting GQDs(the wavelength of the maxium emission locates at 600 nm with a QY of 18%). Meanwhile, for a deeper understanding of the FL mechanism of the as-prepared GQDs, the inherent relationship between the emission behavior and its composition, particle size, surface state has been studied systematically. Second, based on the pH-sensitive optical properties of the green emititing GQDs, fluorescent sensing system has been built for the detection of urea and the method has been applied to the determination of urea in human serum samples. Finally, this paper makes research about the exploitation of red emiting GQDs for bio-imaging and its resistance to fluorescence interference from biological matrix. Based on the folate receptor-mediated targeting, superior biocompatibility of liposome, folate-targeted liposome embedding the fluorescent graphene quantum dots has been prepared and targeting imaged the MCF-7 cells. The research achievement provides graphene quantum dots a simple and effective method for targeting labeling or sensing. Dissertation is divided into three chapters, the specific content is as follows:In chapter 1, introduction, the natures, synthetic methods and applications of CQDs were summarized. Based on the present situation and the trend of fluorescent CQDs at home and abroad, the ideas of dissertation were presented.In chapter 2, based on a reformative oxidation strategy using high concentration nitric acid, alcohol lamp soot was the cabon source, green emitting GQDs with a QY of 50% were obtained and characterized.In chapter 3, alternative cabon source of activated carbon was chosed, red emitting GQDs with a QY of 18% were synthesized and characterized. The mechanism of FLwas investigated deeply.In chapter 4, a novel and well-designed fluorescent sensing strategy based on pH-sensitive green GQDs(synthesized by concentrated nitric acid oxidation of the alcohol lamp soot) has been proposed for urea assay.In chapter 5, the bio-imaging appilication of the as-prepared red GQDs and the resistance to fluorescence interference from biological matrix were exploited in detail.In chapter 6, based on the folate receptor-mediated targeting, superior biocompatibility of liposome, folate-targeted liposome embedding red emiting GQDs has been prepared and characterized by fluorescence spectrum and transmission electron microscope(TEM). Targeting imaging of the MCF-7 cells has been achieved by folate-targeted liposome embedding the red emiting GQDs.Finally, the full texts of dissertation were summarized and the follow-up research ideas were proposed.