Showing papers by "Richard D. Tilley published in 2011"

How Nanoparticles Coalesce: An in Situ Study of Au Nanoparticle Aggregation and Grain Growth

Abstract: The processes of aggregation and subsequent grain growth of highly twinned, surfactant stabilized gold nanoparticles have been followed in real time using synchrotron X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS). This gives insight into the overall coalescence mechanism of metal nanocrystals. First, the capping ligands melt or desorb, which enables the nanocrystals to aggregate and join together. At longer times, grain growth is observed, and the stacking fault densities decrease. The time scale of the grain growth process is significantly longer than that of the particle aggregation. We contrast the behavior we observe to that of other nanoparticles and discuss the implications of our results on device fabrication.

Simple Synthesis and Functionalization of Iron Nanoparticles for Magnetic Resonance Imaging

Abstract: Magnetic nanoparticles (NPs) are increasingly important in many biomedical applications, such as drug delivery, hyperthermia, and magnetic resonance imaging (MRI) contrast enhancement. For MRI, iron oxide NPs are the only commercial T2 or negative contrast agents, due to their biocompatibility and ease of synthesis and research in the area is highly active. The efficacy of these contrast agents depends mainly on the surface chemistry and magnetic properties of the NPs. Materials with larger magnetization could induce more efficient transverse (T2) relaxation of protons and result in greater contrast enhancement. As iron has the highest saturation magnetization at room temperature among all elements, and is biocompatible, it is an ideal candidate for MRI contrast enhancement. Nevertheless, the development of using iron NPs for magnetic applications has been challenging and limited compared to those of its oxides, due to the difficulty in preparing stable iron NPs with simple synthesis methods and precursors. 6] Under ambient conditions, iron NPs of 8 nm or smaller oxidize completely upon exposure to air. For larger NPs, an oxide shell of 3–4 nm forms instantly on the surface, forming iron/iron oxide core/shell NPs. Groundbreaking studies for the synthesis of iron NPs of larger than 8 nm has largely been achieved by decomposition of iron pentacarbonyl, [Fe(CO)5]. [6,8] Additional reports include the use of other precursors in forming iron nanocubes. However, all of these processes are limited in terms of ease of synthesis and scalability; [Fe(CO)5] is volatile and highly toxic, [5] and other processes involve precursors that are expensive and airsensitive, or require high decomposition temperatures. Here, we chose an easy to handle iron organometallic sandwich compound as the precursor and prepared singlecrystal iron NPs using a simple, low-temperature synthesis method. The iron nanocrystals oxidized naturally to form highly crystalline iron/iron oxide core/shell NPs. The ease of this synthesis facilitates the larger-scale application of stabilized iron NPs. To enable the use of these NPs in biological applications, the NP surface was modified to make the NPs water soluble. The strongly magnetic core/shell NPs are shown to be more effective T2 contrast agents for in vivo MRI and small tumor detection, compared to pure iron oxides. The successful detection of small tumors in vivo demonstrated here holds a great promise for accurate detection of early metastases in human lymph nodes, which has a large impact on the treatment and prognosis of a range of cancers. The iron/iron oxide core/shell NPs were prepared by first synthesizing iron nanocrystals by decomposition of the iron precursor [Fe(C5H5)(C6H7)], in the presence of oleylamine (OLA) stabilizing molecules. The non-carbonyl, sandwich compound was chosen for its simple preparation and ease of decomposition compared to other more stable sandwich compounds such as ferrocene. The synthesis was carried out in a closed reaction vessel under a mild hydrogen atmosphere, at 130 8C. The temperature required was lower than the usual temperature range (150–300 8C) needed for decomposition of other iron precursors in previous studies. Once [*] Dr. K. W. Feindel, Prof. P. T. Callaghan, Prof. R. D. Tilley School of Chemical and Physical Sciences and The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6012 (New Zealand) Fax: (+ 64)4-463-5237 E-mail: richard.tilley@vuw.ac.nz Dr. S. Cheong, Dr. B. Ingham Industrial Research Limited and The MacDiarmid Institute for Advanced Materials and Nanotechnology P. O. Box 31-310, Lower Hutt 5040 (New Zealand) Dr. P. Ferguson, Dr. I. F. Hermans Malaghan Institute of Medical Research P. O. Box 7060, Wellington 6012 (New Zealand)

Sized controlled synthesis, purification, and cell studies with silicon quantum dots

Abstract: This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using 1H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.

Synthesis and Comparison of the Magnetic Properties of Iron Sulfide Spinel and Iron Oxide Spinel Nanocrystals

Abstract: Mondispersed Fe3S4 nanocrystals were made by in situ sulfidization of the decomposition product of Fe(acac)2. Monodisperse Fe3O4 nanocrystals were also made by a similar route and the magnetic properties compared.

Solution Synthesis and Optical Properties of SnTe Nanocrystals

Abstract: A facile approach has been developed for the synthesis of SnTe nanocrystals using triethanolamine as the stabilizing agent. The size of SnTe nanoparticles can be readily tuned from 2.7 to 32 nm. Powder X-ray diffraction and selective-area electron diffraction (SAED) indicate that the nanoparticles adopt the cubic rock-salt crystal structure. The direct band gap of the resulting nanoparticles can be significantly tuned and blue-shifted relative to the bulk value by changing the nanocrystal size.

Shape Control of Platinum and Palladium Nanoparticles for Catalysis

Abstract: Platinum and palladium are important catalysts for a wide variety of industrial processes. With the increasing demands of these materials, the development of high-performance catalysts is an important area of research, and as a result, shape control synthesis has become one of the leading research focuses. This minireview surveys the different approaches in solution-phase synthesis that have been successfully adopted for achieving shaped platinum and palladium nanoparticles that are enclosed with specific crystallographic facets. In addition, catalytic studies of the shaped nanoparticles are highlighted, in which promising results have been reported in terms of enhanced activity and selectivity. The future outlook discusses the aspects in synthesis and catalysis to be considered for the development of highly efficient and effective catalysts.

Toxicity test: Fluorescent silicon nanoparticles

Abstract: Semiconductor nanoparticles ('quantum dots', QDs) are useful fluorescent materials because of their high fluorescent stability compared with existing organic fluorescent dyes. QDs were tested in many biochemical experiments, and the reported results suggested their advantages. However, when we consider their application at the clinical level, their large-scale use may be problematic because of their influence on the environment and the living body as a result of cadmium contained in existing mainstream QDs. Here we report on the characteristics of silicon particles (synthesised using the gas phase method and liquid phase method, currently in the development stage) as a substitute material, focusing on cell-level safety and the potential mechanisms of toxicity.

Healing and sealing carbon nanotubes—growth and closure within a transmission electron microscope

Abstract: The growth of carbon nanotubes, and the role of the catalyst in this process, is only partially understood. Here we report real-time TEM observations of a partially embedded crystalline catalyst particle retracting from the hollow of a growing carbon nanotube, followed by a subsequent closure of the tube. The retraction is explained by size-dependent capillary forces, demonstrating the importance of capillary forces in the interaction between the catalyst and the nanotube. The observed crystallinity of the particle provides evidence that carbon nanotube growth in these circumstances does not require a molten catalyst, and closure of the tube suggests a carbon concentration gradient is involved in the growth.