Thi Dieu Thuy Ung

CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ~500 and 700 nm with the luminescence quantum yield (LQY) of 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml−1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng μl−1 with a detection limit of 3 ng μL−1 has been performed based on the antibody-antigen recognition.

Synthesis and characterization of nano-CuO and CuO/TiO2 photocatalysts

CuO nanocrystals were prepared by thermal decomposition of Cu-oxalate at 400 °C; then CuO/TiO2 core/shell nanocrystals were formed via the hydrolysis of titanium isopropoxide (TIP) on the surface of CuO nanocrystals. The characteristics of the synthesized nanocrystals were systematically studied using appropriate techniques, namely the morphology by using scanning electron microscopy (SEM), and the crystalline structure by x-ray powder diffraction (XRD) and Raman spectroscopy. The structure, shape and size of the CuO and CuO/TiO2 nanocrystals could be tuned by changing various technological parameters: (i) the reaction/growth time (from several minutes to several hours), (ii) reaction temperature (from room temperature to 90 °C) and (iii) the molar ratios of the precursors. The results showed that the reaction temperature and the molar ratio of the precursors play important roles in controlling the morphology and size of both CuO and CuO/TiO2 nanocrystals. With increasing reaction temperature, nano-CuO evolved from spherical shaped nanoparticles to microspheres. By shelling the large-bandgap TiO2 layers on CuO nanocrystals, the core/shell structure is formed and the narrow-bandgap nano-CuO core is expected to be resistant to photocorrosion.

Fluorescence biosensor based on CdTe quantum dots for specific detection of H5N1 avian influenza virus

This report highlights the fabrication of fluorescence biosensors based on CdTe quantum dots (QDs) for specific detection of H5N1 avian influenza virus. The core biosensor was composed of (i) the highly luminescent CdTe/CdS QDs, (ii) chromatophores extracted from bacteria Rhodospirillum rubrum, and (iii) the antibody of ?-subunit. This core part was linked to the peripheral part of the biosensor via a biotin?streptavidin?biotin bridge and finally connected to the H5N1 antibody to make it ready for detecting H5N1 avian influenza virus. Detailed studies of each constituent were performed showing the image of QDs-labeled chromatophores under optical microscope, proper photoluminescence (PL) spectra of CdTe/CdS QDs, chromatophores and the H5N1 avian influenza viruses.

Synthesis, structural and photocatalytic characteristics of nano-Cu2−xSe

Large-scale synthesis of Cu2?xSe nanocrystals (nano-Cu2?xSe) with uniform size was performed via a facile hydrothermal method at room temperature and at 120??C. Nano-Cu2?xSe with different structures could be synthesized by changing the reaction/growth time, the Cu:Se molar ratios, and the initial concentration of the precursors. The synthesized nano-Cu2-xSe was characterized using various techniques, including x-ray powder diffraction, scanning electron microscopy and photocatalytic activity. Systematic studies showed that the reaction time played a key role in controlling the morphology and structure leading to significant influence on the photocatalytic activity of nano-Cu2?xSe. With increasing reaction/growth time, Cu2?xSe could transform gradually from a cubic to hexagonal structure and from nanoparticles to nanoplate/nanorod shapes. The photocatalytic characteristics were evaluated by the photo-decoloration of Rhodamine B (RhB) in aqueous solution under visible light irradiation. As-prepared nano-Cu2?xSe showed good photocatalytic activity under visible light irradiation, indicating potential applications in depollution technologies.

Attaching quantum dots to HER2 specific phage antibodies

This work presents the results of the attachment of Qdot 655 ITK TM amino (PEG) quantum dots (QDs) (Invitrogen) and CdTe QDs (provided by Institute of Materials Science, VAST) to HER2 (Human Epidermal growth factor Receptor 2) specific phage antibodies (Abs) (provided by Institute of Biotechnology, VAST) in solution. The QDs were attached to the phage display specific HER2 Abs to form a complex QD‐Ab. The QDs and complex QD‐Ab were characterized by UV-VIS spectroscopy, transmission electron microscopy (TEM) and fluorescence microscopy. The fluorescence images show the QDs conjugated to the phage. Due to the QDs attaching to the surface, the phage dimensions were amplified, so its shape could be observed by optical microscopy. The complex QD‐Ab was stable and lasted for a month. The results illustrate the value of the HER2 phage‐QD complex as a cancer detection platform.

Non-chapped, vertically well aligned titanium dioxide nanotubes fabricated by electrochemical etching

This paper reports on the fabrication of non-chapped, vertically well aligned titanium dioxide nanotubes (TONTs) by using electrochemical etching method and further heat treatment. Very highly ordered metallic titanium nanotubes (TNTs) were formed by directly anodizing titanium foil at room temperature in an electrolyte composed of ammonium fluoride (NH4F), ethylene glycol (EG), and water. The morphology of as-formed TNTs is greatly dependent on the applied voltage, NH4F content and etching time. Particularly, we have found two interesting points related to the formation of TNTs: (i) the smooth surface without chaps of the largely etched area was dependent on the crystalline orientation of the titanium foil; and (ii) by increasing the anodizing potential from 15 V to 20 V, the internal diameter of TNT was increased from about 50 nm to 60 nm and the tube density decreased from 403 tubes μm−2 down to 339 tubes μm−2, respectively. For the anodizing duration from 1 h to 5 h, the internal diameter of each TNT was increased from ~30 nm to 60 nm and the tube density decreased from 496 tubes μm−2 down to 403 tubes μm−2. After annealing at 400 °C in open air for 1 h, the TNTs were transformed into TONTs in anatase structure; further annealing at 600 °C showed the structural transformation from anatase to rutile as determined by Raman scattering spectroscopy.

Time-resolved photoluminescence and photostability of single semiconductor quantum dots

Time-resolved photoluminescence (TRPL) and photostability were studied for several core/shell-type semiconductor quantum dots (QDs) of CdTe/CdS, In(Zn)P/ZnS and CdZnS/ZnS using a TRPL microscopy at a single QD level, of which results were compared to that of CdSe/ZnS QD. The CdTe/CdS and In(Zn)P/ZnS QDs show unstable PL at a single QD level on both bare and polymer-coated glass coverslips, so that they mostly lose emissions within a few seconds. The CdZnS/ZnS QD shows better emission stability than those of the former two QDs, but still less stable than the case of the CdSe/ZnS.

Square-inch 2D-arrays of Au nanodisks fabricated by sputtering Au onto anodic aluminum oxide templates for SERS applications

Two-dimensional (2D) arrays of gold nanodisks (Au NDs) with different sizes of 75, 95 and 115 nm, with the distances between NDs of 10, 30 and 50 nm were fabricated on square-inch substrates. The optimal conditions regarding the thickness of anodic aluminum oxide (AAO) template, sputtering time and annealing temperature for Au, lift-off the walls of AAO template for getting the highest quality 2D arrays of Au NDs have been determined. Morphology and surface plasmon resonance (SPR) absorption of the 2D arrays of Au NDs were examined by using appropriate techniques. The 2D arrays of fabricated Au NDs show different SPRs peaking in the spectral range of 600–1600 nm, which are very promising for surface-enhanced Raman scattering (SERS)-based sensor applications. As an example for the potential use of fabricated SERS substrates, we have demonstrated the detection of methamidophos at various concentrations ranging from 1 ppb to 103 ppm. Moreover, the method we have used to fabricate the 2D arrays of Au NDs can be applied to other kinds of metals or alloys just by varying the targets in the sputtering process.

Large 2D-arrays of size-controllable silver nanoparticles prepared by hybrid deposition

Two main results are presented in this paper. (i) Silver nanoparticles (AgNPs) with uniform size-distribution and controllability in the range of 20–50 nm were synthesized by seeding and growing at ambient conditions. The single-crystal Ag nano-seeds were created by reduction of AgNO3 in presence of citrate surfactant at 70 °C. Then, importantly, the fresh AgCl precursor was used in the presence of polyvinylpyrrolidone to adjust the reaction rate with ascorbic acid to generate Ag for growing on the surface of single-crystal Ag nano-seeds. The AgNPs size could be well-controlled by varying the amount of Ag nano-seeds while keeping the AgCl precursor concentration to be constant. (ii) The large 2D-arrays with homogeneous and dense monolayers of AgNPs were prepared on ITO substrates by hybrid method, in which the key technological point is the surface functionalization of AgNPs using mixed alkanethiols (dodecanethiol:octadecanethiol = 6:1). We have used the fabricated 2D-arrays from the 50 nm AgNPs as a surface enhanced Raman scattering substrate to take the Raman scattering spectra of rhodamine B (RhB), glucose and viral pathogen (H5N1) at very low concentrations of 10−10 M, 10−12 M and 4 ng μl−1, respectively.