The Preparation And Application Of Flourescent Carbon Dots

As a group of newly emerged fluorescent nanomaterials, carbon dots(CDs) are superior to semiconductor quantum dots and organic dyes because of their high solubility, robust chemical inertness, facile modification and high resistance to photobleaching, making them great potential in bioimaging, photocatalysis, fluorescence sensors, optronics, etc. Reports on this topic are gradually mature, however, most of these reported CDs emit blue fluorescence under ultraviolet excitation. On the other hand, complex procedures for their separation and purification or low product yield are some of the issues that need to be tackled. Therefore, this paper will be carried out as the following three parts work, focusing on the synthesis methods and novel applications of the multifunctional fluorescent CDs.In section 2, we report a facile method to prepare stable CDs by hydrothermal treatment of glucose(glc) in the presence of glutathione(GSH). With this approach, the formation and the surface passivation of CDs were carried out simultaneously, resulting in intrinsic fluorescence emission. The influence of reaction temperature, reaction time and feed ratio of GSH/glc on the photoluminescence property of CDs were studied. The as-prepared CDs were characterized by UV, PL, TEM, FTIR, and XPS, from which their structural information and property were interpreted. Owning to their pronounced temperature dependence of the steady-state fluorescence emission spectra and pH-responsive behavior, resultant CDs showed great potential as versatile nanothermometry devices by taking advantage of the temperature sensitivity of their emission intensity, which changed considerably over the physiological temperature range(15-60℃), as well as a promising candidate in pH sensor. In order to extend the hydrothermal method, we used citric acid(CA) as carbon source and hyperbranched polyethyleneimine(PEI) as surface passivation agent to prepare fluorescent CDs. Resultant CDs exhibited strong blue fluorescence and could be used in pH sensing, cellular imaging.In section 3, we report the preparation of the amphibious yellow luminescent CDs(Y-CDs) by using a rapid and low-cost microwave pyrolysis method. The Y-CDs exhibited excellent solubility and strong yellow luminescence both in water and organic solvents. Importantly, the presence of Cr(VI) ions could be revealed by the fluorescence color changes of the Y-CDs. The as-prepared Y-CDs could be used to detect Cr(VI) through fluorescent colorimetric method, which showed a high sensitivity and selectivity for Cr(VI) ions. The limit of detection could reach as low as 0.02 μM. Moreover, we have created Cr(VI) test papers for visual on-site sensing of Cr(VI). We have also shown that the as-prepared Y-CDs could be conveniently utilized to fabricate light-emitting polymer composite film with high optical performance. Considering the facile fabrication process and Cr(VI)-deduced emission color change for the amphibious Y-CDs, this work may bring us a bright prospect in practical applications such as bioimaging, optical devices, and visual on-site sensor for Cr(VI)In section 4, fluorescent CDs loaded on SiO2 spheres were synthesized by the one-pot hydrothermal route, and then folic acids(FA) were covalently conjugated on the surface of SiO2 spheres. The formed SiO2@CDs-FA composites could target specific tissues, e.g., cancer. The key of this method was the employment of(3-Aminopropyl)trimethoxysilane(APS) as bridge joint, which not only served as surface passivation agents allowing the production of CDs with high quantum yield, but also enabled SiO2@CDs composites further covalent conjugation of FA. The resultant SiO2@CDs composites were highly stable, well water-soluble, and biocompatible. Moreover, the SiO2@CDs-FA could be used as fluorescent probes for biological imaging in vitro. Our results demonstrated that SiO2@CDs-FA could specifically target cancer cells by the receptor-mediated delivery pathway within a short time incubation. Findings from this study suggested that the SiO2@CDs-FA composites could be used as a platform for cancer diagnosis studies.