Synthesis Of Carbon Quantum Dots (CDs) And Its Application In Analysis Of Food

With the living standards improved and more and more serious pollution problems caused by global industrial development, food safety problems have gradually causing great concern at home and abroad. In recent years, nanotechnology has become one of the hot topics of global research. Unique physical and chemical properties of nano-materials, nano-technology so widely used in the field of the food testing, including the detection of heavy metals, pesticide residues and organic small molecule detection.Carbon quantum dots because of low toxicity, good biocompatibility, chemical stability and good solubility in water, has potential applications in many fields of biological imaging, immunoassay, organic analysis, especially analysis of small organic molecules application identification and detection in the field of the expanding carbon quantum dots of another hot research.Carbon quantum dots(CDs) is formed of sp2 bonded carbon or amorphous carbon, steady glow, with a spherical structure of nanoparticles, have attracted increasing attention in recent years because of their interesting properties, such as water solubility, biocompatibility, good photostability and low cytotoxicity. These make CDs good alternative to QDs for sensing organic small molecule and other bio-species in food, environment and biological samples. CDs fluorescent nanosensor for organic small molecules with wide linear range, high sensitivity and less interference of fluorescence spectrum, moreover, spectrophotofiuorometer ’s prices is inexpensive, require small amounts of sample without pre-treatment of complicated process. Although CDs fluorescence nanosensor has many advantages, but it still has some problems in practical application: these CDs have low quantum yield and poor metalloform-selective.For these problem this subject main for has following research:(1) Organosilane modified carbon dots(CDs) was prepared using N-(β-aminoethyl)-γ-aminopropyl methyldimethoxysilane(AEAPMS) as the main raw material and they were doped into silica nanoparticles by silylation reaction.A new fluorescence quenching method for determination of KBrO3 is proposed. The method was based on the fact that the fluorescence intensity was decreased greatly by the oxidization of KBrO3 with HCl media. Several important parameters affecting the performance of the nanosensor were investigated and optimized. The detection limit of this nanosensor was 1.1 ng·m L-1 with a linear range from 20 to ~500 ng·m L-1. Use of delta rule, it has been applied successfully to determine KBrO3 in the water sample with satisfactory results.(2)Anhydrous citric acid as the carbon source and n-(β-aminoethyl-γ-Aminopropyl) methyl-methoxy-silane as the reactants, CDs was prepared by thermal cracking. Afterwards, silica nanoparticles as interconnect medium, Rhodamine B, which is a kind of organic fluorescent dye, and CDs were both connected onto the surface of silica nanoparticles. So the CDs coated dual-emission silica nanoparticles were obtained. This dual-emission nanoparticles combining tow different fluorophores, which are CDs and RhB, and fluorescence intensity of CDs was the analytical signal, fluorescence intensity of RhB was act as reference signal.A simple and effective strategy for designing ratiometric fluorescent nanosensor has been described in this work. A carbon dots(CDs) based dual-emission nanosensor for NO2-was prepared by coating CDs on the surface of dye doped silica nanoparticles. In hydrochloric acid media(0.01 M), the fluorescence of dual-emission silica nanoparticles was quenched by potassium bromate(KBrO3) oxidating effect, and the oxidation of CDs coated dual-emission silica nanoparticles by potassium bromate(KBrO3) is catalyzed by NO2-, resulting in the ratiometric fluorescence response of the dual-emission silica nanoparticles. Several important parameters affecting the performance of the nanosensor were investigated and optimized. The detection limit of this nanosensor was 1.0 ng·m L-1 with a linear range from 10 to 160 ng·mL-1. It has been applied successfully to determine NO2- in the food and water with satisfactory results.(3) For CDs doped silica nanoparticles(SiO2 @ CDs), the fluorescence of SiO2 @ CDs was quenched by Cu2+; and the fluorescence of SiO2 @ CDs was recovered based on the strong binding ability of Cu2+ and L-cystenine(-SH). So a turn-off-on fluorescence assay was developed, and the method was optimized in detail. The detection limit of this fluorescence quenching- restore method was 2.8×10-7 mol·L-1, the linear range of 0.2×10-5~ 1.5×10-5 mol·L-1. The analytical result for the certified reference health food sample was in a good agreement with the certified value. The parameters affecting the performance of the probe, such as pH, reaction temperature and time were investigated and optimized.