The Synthesis Of Water-Soluble Quantum Dots And Its Analytical Application

Due to the potential application in biology, water-soluble quantum dots (QDs) have been attracted much attention in recent years. Compared with the synthesis of TOPO-capped QDs, direct preparation of QDs in aqueous solution has several advantages, such as simple, rapid, efficient and low-cost. Up to date, aqueous-phase synthesis of QDs has been developed an important method. In order to improve the quality of QDs and simplify the reaction process, development of a facile method for the synthesis of QDs is also important in the further. Based on the excellent luminescence properties of QDs, development of QDs-based fluorescence immunoassay for the detection of disease of animals is extremely suitable for detecting, preventing, or controlling animal-borne disease outbreaks.In addition, the chemiluminescence (CL) and electrogenerated chemiluminescence (ECL) properties of QDs were seldom investigated. Therefore, development of QDs-based CL and ECL methods for the analysis of heavy metal ions and hydrogen peroxide with high sensitivity are very important in soil environment protection field and active oxygen detection. The main results were as follows:(1)A novel method for the preparation of water-soluble and small-particle size CdSe QDs has been proposed under high-intensity ultrasonic irradiation. The as-prepared products have been characterized by Ultraviolet-visible (UV-vis) absorption spectra, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM).A possible reaction mechanism was also investigated.(2) A simple, rapid, cost-efficient and convenient method has been developed for synthesis of water-soluble CdTe QDs in ambient atmospheric conditions.Using this method, the preparation of Te precursor and growth of CdTe QDs were achieved with one-step synthesis route. Under the optimal conditions, the as-prepared CdTe QDs possessed a high photoluminescence quantum yield (84%), a narrow size distribution (full width at half maximum=30 ran), small particle size (2.6nm) and low cytotoxicity. The photoluminescence and ECL behaviors of as-prepared CdTe QDs show their potential application in cell imaging and ECL biosensing with high sensitivity.(3)We detected the antibody of Actinobacillus Pleuropneumoniae (APP) using a QDs-based indirect fluroimmunoassay. Under the optimal conditions, the linear range for the dilution coefficient of the ApxIV antibody (standard positive serum) was in the dilution range of 1:8-1:512.The limits of detection (LOD)for the assay was 1100 times dilution of standard positive serum. Compared with the LOD of ApxⅣ-ELISA (320 times dilution) and IHA(128 times dilution), the proposed method had a higher sensitivity for the determination of ApxⅣantibody of APP.This is the first investigation for measuring the ApxIV antibody via the quenching effect of AuCl4- to QDs, and it showed great potential for numerous applications in immunoassays. We believe that the proposed method is extremely suitable for detecting, preventing, or controlling animal-borne disease outbreaks.(4) We have developed QDs-AuCl4--based immunochromatographic strip biosensor for the simple, rapid and sensitive detection of avian influenza (AI) virus.Under the optimal conditions, the linear range for the concentration of AI virus was in the range of 2.7×10-9-3.2×10-8 g/mL. The LOD for the assay was 9.0×10-10g/mL. This sensor has the benefits of conventional GITS and high sensitivity of QDs probe, and shows potential application in animal-borne disease. Compared with previously reported methods, the proposed method had high sensitivity for the detection of AI virus. In combination with multiplex GITS,this sensor will allow multiplexed detection of viruses and will make a portable device possible for point-of-care applications.(5) The behaviors of 15 kinds of metal ions in the thiol-capped CdTe QDS-H2O2 CL reaction were investigated in detail. The results showed that Ag+, Cu2+ and Hg2+ could inhibit CdTe QDs and H2O2 CL reaction. A novel CL method for the selective determination of Ag+, Cu2+ and Hg2+ was developed, based on their inhibition of the reaction of CdTe QDs and H2O2. Under the optimal conditions, good linear relationships were realized between the CL intensity and the.logarithm of concentrations of Ag+,Cu2+ and Hg2+.The linear ranges were from 2.0×10 to 5.0×10-8 mol/L for Ag+, from 5.0×10-6 to 7.0×10-8 mol/L for Cu2+ and from 2.0×10-5 to 1.0×10-7 mol/L for Hg2+, respectively. The LOD (S/N=3) were 3.0×10-8,4.0×10-8 and 6.7×10-8 mol/L for Ag+, Cu2+ and Hg2+, respectively. A possible mechanism for the inhibition of CdTe QDs and H2O2 CL reaction was also discussed.(6) The ECL from thiol-capped CdTe QDs was investigated.The ECL emission was occurred at-1.1 V and reached a maximum value at-2.4 V when the potential was cycled between 0.0 and-2.5V. The reduced species of CdTe QDs could react with the coreactants to produce the ECL emission. The CdTe QD concentration(6.64×10-7 mol/L)of ECL is lower than that (1.0×10-3 mol/L)of CL. Based on the enhancement of light emission from thiol-capped CdTe QDs by H2O2 in the negative electrode potential, a novel method for the determination of H2O2 was developed. The light intensity was linearly proportional to the concentration of H2O2 between 2.0×10-7 and 1.0×10-5 mol/L with a LOD of 6.0×10-8 mol/L.Compared with most of previous reports, the proposed method has higher sensitivity for the determination of H2O2. In addition, the ECL spectrum of thiol-capped CdTe QDs exhibited a peak at around 620 nm, which was substantially red shifted from the FL spectrum, suggesting the surface states play an important role in this ECL process.