Synthesis And Application Of Water-Soluble Quantum Dots In Food Detection

Quantum dots, as a specific and new class of fluorescent probes, have the ideal advantage such as broad excitation spectrum, narrow-band emission spectrum, high chemical stability, long fluorescence lifetime and the resistance to photobleaching compared to the traditionary fluorescent dye. Quantum dots played a more important roles in biology, chemistry, and molecular biology in recent years. Referring a lot of data, the work of predecessor was summarized. And the works such as quantum dots preparation, characterization and quantum dots application in hazard and nutrition factors in food were completed.High fluorescent and stable ZnSe quantum dots were synthesized by a facile colloid aqueous phase route. It overcame the defects such as unstable and low quantum yields of the quantum dots which synthesized by early aqueous phase route. Optimum conditions were found. L-glutathione used as the stabilizer, the molar ratio of L-glutathione, Se2-and Zn2+ is 5:1:5, the reaction media is pH 10.5, and the proper temperature is between 90℃and 100℃. Quantum yields (QYs) could reach to 50.1% without post irradiation in prime synthetical conditions. And the fluorescence intensity of ZnSe QDs almost didn't change after 3 months. Its water-soluble property is also excellent. The properties of ZnSe QDs were characterized by means of ultraviolet visible spectra and fluorescence spectra, transmission electron microscopy. The synthesized ZnSe QDs emit blue-purple fluorescence(370 nm)when it was excited at 300 nm. And the excellent photochemical characteristics of the ZnSe QDs will have advantageous in the application of light hot manufacture and chemistry biology domain.We apply new ZnSe quantum dots (QDs) which are prepared in water phase to detection of metal ions. According to the interaction of effective functional group and Pb2+ion, a new fluorescence quenching method determining Pb2+ ion with quantum dots as fluorescent probe is establishied. The reasons of fluorescence quenching are also explained on the mechanism. The fluorescence quenching of the ZnSe QD depended on the concentration, pH of the solution, reaction time and other factors of the Pb2+ solution. Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of ranging from 1.0×10-8～8.0×10-7 mol/L.The regression coefficient is 0.999 and limit of detection for Pb2+ was 0.71 nmol/L.This developed method is demonstrated improved sensitive and selectivity characteristics for the detection of trace Pb2+We synthesize CdSe quantum dots directly under non-oxygen, stirring, and using the NaHSe, CdCl2 as precursor and L-glutathione as stabilizer. We also study the effects of pH, time and temperature to the quantum dots fluorescent. In addition, transmission electron microscopy, ultraviolet visible spectra, fluorescence spectrum were used to characterized the CdSe QDs. The research was to develop a new fluorescence measurement method for detection of Escherichia coli(E.coli) count by using water-soluble CdSe QDs. The bacterial images were obtained using fluorescence microscopy. The results showed that CdSe QDs were highly stable, high quantum yield and successfully conjugated with E.coli. The method could detect 103-109 cfu/mL of E.coli rapidly. The low detection limit is 102 cfu/mL. The relationship of the intensity and log total count of E.coli have been establishied as the equation F=23.955C+362.91(r2=0.9923)Fluorescence resonance energy transfer (FRET) system was constructed between CdSe QDs (donor) and rhodamine B(RhB) (acceptor). Several factors which impacted the fluorescence spectra of the FRET system were studied. The feasibility of the prepared FRET system as fluorescence probe for detecting vitamin B12 in aqueous solution was demonstrated. A good linear relationship showed between the increasing of the concentration of VB12 in the range of 1.0×10-5-1.6×10-3mol/L and the reducing of the fluorescence intensity of CdSe QDs-RhB FRET system. Based on this, water-soluble VB12 was detected. The linear correlation coefficient R2 was 0.993, the detection limit was 2.3×10-7mol/L.