Huanbo Wang

Hydrothermal synthetic mercaptopropionic acid stabled CdTe quantum dots as fluorescent probes for detection of Ag

Mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) with particle size 3 nm have been successfully synthesized in aqueous medium by hydrothermal synthesis method. And the effects of different metal ions on MPA capped CdTe QDs fluorescence were studied using fluorescence spectrometry. The results demonstrated that at the same concentration level, Ag(+) could strongly quench CdTe QDs fluorescence, and the other metal ions had little effect on CdTe QDs fluorescence except Cu(2+). On the basis of this fact, a rapid, simple, highly sensitive and selective method based on fluorescence quenching principle for Ag(+) detection in aqueous solution was proposed. Under optimal conditions, the quenched fluorescence intensity (F(0)-F) increased linearly with the concentration of Ag(+) ranging from 4 × 10(-7) to 32 × 10(-7)mol L(-1). The limit of detection for Ag(+) was 4.106 × 10(-8)mol L(-1). The obtained plot of F(0)/F versus [Ag(+)] was an upward curvature, concave towards the y-axis, rather than a straight line. The modified form of the Stern-Volmer equation was third order in Ag(+) concentration. According to the modified Stern-Volmer equation, it can be inferred that dynamic quenching and static quenching simultaneously occurred when Ag(+) interacted with MPA capped CdTe QDs. At the same time other factors might also influence the quenching process. Based on this study, hydrothermal synthesized MPA capped CdTe QDs with particle size 3 nm may be used as a novel fluorescence probe to quantificationally and selectively detect Ag(+).

Application of excitation–emission matrix fluorescence combined with second-order calibration algorithm for the determination of five polycyclic aromatic hydrocarbons simultaneously in drinking water

Direct determination of five polycyclic aromatic hydrocarbons including fluorene, anthracene, phenanthrene, pyrene and fluoranthene was accomplished by excitation-emission matrix fluorescence coupled with chemometric methods based on an alternating trilinear decomposition (ATLD) algorithm. A uniform design and orthogonal design are proposed for the creation of the calibration set. Results showed that no significant difference in the recoveries for each of the PAHs was observed. Thus, both of the designs can be used for the calibration set. In addition, some statistical parameters and figures of merit, such as average recovery, root-mean-square error of prediction, sensitivity, and selectivity were investigated to evalute the performance of the proposed method. The results showed that fluoranthene was the most selective, whereas fluorene was more sensitive than any other compound. This method was also employed for the determination of samples of drinking water spiked with all these PAHs. It can be observed that the results were not as satisfying as those in synthetic samples due to the negative effects of humic acid or fulvic acid in drinking water.

Monitoring fluorescence quenching of polycyclic aromatic hydrocarbons by humic acid in water using fluorescence fingerprints

Fluorescence measurements on selected polycyclic aromatic hydrocarbons were performed to obtain the information about the fluorescence quenching of polycyclic aromatic hydrocarbons by humic acid. The fluorescence properties of pyrene and fluoranthene in the presence of humic acid in water were investigated by three dimensional excitation-emission matrix fluorescence spectroscopy. The pH influence on the fluorescence quenching of pyrene and fluoranthene were also investigated. For both pyrene and fluoranthene, the fluorescence quenching were dominated by static quenching processes. According to the result of the research, the effect of humic acid on the pyrene and fluoranthene can be calibrated in the water environment. The results show that three dimensional excitation-emission matrix fluorescence spectroscopy has great potential for the use of in-situ measurement of polynuclear aromatic compounds in water environment.

Study of measuring the intensity distribution of LED with lock-in amplifier

By using Digital Lock-in Amplifier LI5640, the intensity distribution of LED is measured, meanwhile compared with two other common measuring methods with the internal modulation. The structure of the research system, the transmitter module, the optical receiving module, the research light path and Digital Lock-in Amplifier LI5640 are all introduced and the analysis based on research results is given. Its proved that the Lock-in Amplifier is superior for weak light signal detecting; also this research system can be the reference of correlative research designs.

Simultaneous determination of Benzo(k)fluoranthene and Perylene using Excitation-Emission Matrix Fluorescence

Benzo[k]fluoranthene (BkF) and perylene (Per) are among the sixteen priority pollutants of polycyclic aromatic hydrocarbons recommended by The United States Environment Protection Agency (EPA). In this paper, we report a simple and rapid method for quantitative analysis of BkF and Per using the three-dimensional excitation-emission matrix (EEM) fluorescence coupled with parallel factor analysis (PARAFAC). Before analyzing of two mixtures quantitatively, we study the fluorescence characterization of pure BkF and Per first. The maximal peak values are at 306 nm of the excitation wavelength and 406 nm of the emission wavelength for BkF, and 252 and 438nm for Per, the linear ranges of BkF and Per are 0.8~16~ L-1 and 0.6~20~ L-1 respectively. Finally the average recoveries are obtained using PARAFAC algorithm, which can reach 101.1% and 99.5% for BkF and Per respectively. In order to evaluate the accuracy of the PARAFAC algorithm, selectivity (SEL) and sensitivity (SEN) have also been presented. Results show that a good performance has been achieved using excitation-emission fluorescence coupled with PARAFAC algorithm.