| Carbon dots (CDs), as a new fluorescence carbon nanomaterial, possess unique optical properties and small size effects, with good biocompatibility and without cytotoxicity. In recent years, quantum dots (QDs) have been widely applied to the fields of biology and medicine owing to their unique fluorescent properties. Regrettably, the heavy metals in the QDs, such as cadmium, have serious cytotoxicity, at the same time, QDs have light blinking phenomenon, which limited their practical applications. While CDs could overcome the shortcomings of QDs, and may be a nice substitute for QDs. To date, however, the preparation and application of CDs are at primary stage, and the fluorescence quantum yield is worse than that of QDs. So, exploring good ways to prepare CDs with high fluorescence quantum yield and searching their new applications are quite significant. In this dissertation, we mainly describe the preparation and application of CDs. Firstly, we explored one new route to synthesize hydroxyls-coated CDs. The obtained CDs have good fluorescence properties. Moreover, the process of synthesis is convenient and economic. Secondly, the hydroxyls-coated CDs were applied to the detection of metal ions. Lastly, carboxyls-functionalized CDs were synthesized according to the reference, and were successfully applied to the detection of lysozyme in Lysozyme Buccal Tablets.The main contents of the dissertation consist of the following three parts:(1) The hydroxyls-coated CDs were facilely synthesized by hydrothermal reaction of candle soot in sodium hydroxide aqueous solution. They possessed excellent properties, such as good fluorescence performance, good water-solubility, anti-photobleaching, high salt tolerance, and low cytotoxicity. Transmission electron microscope (TEM) showed that CDs were uniformly distributed with the diameter of 3.1±0.5 nm. For further analysis the size in aqueous solution, dynamic light scattering (DLS) was employed and the results showed that they were also uniformly distributed with an average diameter of about 10 nm. With fourier transform infrared (FT-IR) spectrum, we observed that the surface of CDs had many hydroxyls and a few other groups. The CDs reported here have narrow and symmetry excitation and emission spectra, with the peaks at 310 nm and 450 nm, respectively. Furthermore, the CDs have nice florescence property with a fluorescence quantum yield of about 5.5%. However, the quantum yield of the CDs with lots of carboxyls on the surface, obtained by refluxing candle soot and nitric acid, is below 3.0% even by complicated separation or modification process. Based on this, we speculate that carboxyls, with strong electron drawing ability, are not beneficial to the fluorescence emission of CDs when binding to the surface of carbon core directly, while hydroxyls, with strong electron donated ability, are very favourable to the fluorescence emission.(2) We applied the hydroxyls-coated CDs in the detection of metal ions and studied the interaction between them. Some metal ions, whose hydroxides have extremely low solubility product constants, are very easy to combine with the hydroxyls of CDs and link the neighboring CDs. As a consequence, CDs get aggregated, following the fluorescence quenching. According to this, we established a new method for trace amount detection of Cr3+, Al3+ and Fe3+ with CDs as a fluorescent probe, with the detection limits of 3.1,5.1,5.6 ng/mL, respectively. In addition, we found that Al3+ has different phenomenon with the other metal ions. Upon the addition of rising amounts of Al3+, the fluorescence of CDs firstly got quenched and then recovered gradually. The experiment results showed that the quenching process was static quenching wile the recovery process was static and dynamic quenching; DLS results showed that the size of CDs increased in the quenching process, while decreased in the recovery process. We propose that the special phenomenon may be ascribed to the fact that Al3+ is a zwitter ion.(3) The interaction between CDs and lysozyme was studied with resonance light scattering (RLS) technique. In weak alkaline conditions, the negatively charged CDs could bind with positively charged lysozyme through electrostatic attractions, forming a large complex with strong RLS signals which could not be easily influenced by pH and ionic strength. Under the optimum conditions, the enhanced RLS intensity was found to be linearly correlated with the concentrations of lysozyme in the range of 71.5μg/L～14.3 mg/L, with the detection limit of 37.8μg/L (3a). This method was successfully applied to the detection of lysozyme in Lyszome Buccal Tablets with the recovery from 95.8% to 98.9% and the RSD lower than 4.4%. |
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