The handling of metallic nanoparticles often requires their dispersion into several polar and nonpolar solvents. Solid-phase stages or polymer-based ligands are commonly required to complete the transfer. The construction of a thiol ligand based in oleic acid, and its ability to efficiently assist in gold and silver nanoparticle aqueous-organic phase transfer is reported. After the transfer, the particles are completely dispersed in an organic solvent, preserving their diameter and morphology, as confirmed by ultraviolet-visible spectroscopy and scanning transmission electron micrographs.

Organosilica nanoparticles have attracted a lot of research interest in a variety of areas such as drug delivery and catalysis because of their properties which include high surface area as well as tunable particle and pore size. In particular, nanoparticles with large pore sizes are of great interest because of their potential to host large guest molecules such as proteins and as catalysts. The focus of the work in the thesis was to develop phosphonate functionalized organosilica nanoparticles for biomedical and catalytic applications. Raspberry textured phosphonatesilica nanoparticles denoted, RNPPME(2.5) (where the number in the brackets represents the moles of organophosphonate per gram), with large pore size (11–17 nm), uniform particle size (70 – 90 nm) and high surface area were produced through the use of template directed base catalysed synthesis, using tetraethylorthosilicate (TEOS) and dimethylphosphonatoethyltrimethoxysilane (DMPTMS) as the silica sources. The role of the reaction conditions such as temperature, surfactant concentration, pH, organosilane concentration and type were investigated and a mechanism for the raspberry nanoparticle formation was proposed. The particles were characterized using electron microscopy (SEM and TEM), Dynamic light scattering (DLS), silicon and phosphorus solid state NMR, and solution phase proton NMR of base digested particles, FT–IR, nitrogen adsorption porosimetry and thermal analysis (TGA). The ability of the particles to host protein molecules of the model protein, bovine serum albumin (BSA) was investigated and the particle–protein composite was characterized using circular dichroism (CD). Raspberry textured nanoparticles were found to host large quantities (26 wt%) of protein. Studies on other (small pore (3 nm) phosphonate functionalized nanoparticles NP_PME(0.2) and NP_PME(1.0)) and (3 nm pore) unfunctionalized mesoporous silica nanoparticles (MSN) revealed that phosphonate loading and the pore size influenced the protein uptake In addition to high protein uptake, the RNP_PME(2.5) particles also absorbed protein molecules rapidly (~ 20 minutes to maximum load). CD studies determined that the particle bound protein structure was not affected at physiological pH (7.40). The vast majority of the previously reported studies involving protein immobilization involved the use of bulk silica materials, which cannot be dispersed and hence those materials were unsuitable for in vivo protein delivery applications. The BSA@RNP_PME(2.5) particles showed good protein load and dispersion properties and hence are excellent protein delivery agents. Dispersions of nanoparticle composite BSA#@RNP*_PME(2.5) (where BSA# represents fluorescein isothiocyanate labelled BSA and RNP*_PME(2.5) represents rhodamine B isothiocyanate labelled RNP_PME(2.5)) was used to successfully deliver membrane impermeable protein BSA into HeLa cells. Intracellular protein delivery has attracted great interest due to its potential therapeutic applications and research tool value (e.g. for studying various cellular pathways). The toxicity of the guest free particles RNP*_PME(2.5) and the protein loaded particles BSA#@RNP*_PME(2.5) was studied using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The particles and the protein-particle composite were found to be non-toxic. The mechanism of the particle uptake by the cells was also studied. The unloaded (protein free) particles were found to be taken up by caveolar endocytosis pathway and the protein loaded particles were taken up by folic acid mediated pathway. The results indicated that the particles can successfully deliver membrane impermeable protein across the cell membrane. This result suggested that the particles can potentially be used for intracellular protein delivery applications. Raspberry textured nanoparticles RNP_PME(2.5) were also used to host the enzyme lipase. It was demonstrated that immobilization increased the maximum velocity and Michaelis constant of the enzyme and also that the particles offered protection against the denaturing agent, urea. Finally, in a chemical catalysis application, the RNP_PME(2.5) particles were used to synthesize the platform chemical HMF, through Brönsted acid catalysed dehydration of fructose. High yields of HMF (87 %) were achieved when 10 wt% fructose was used. The particles demonstrated good recyclability and also the ability to convert up to 50 wt% fructose into HMF (80 % yield). The particles therefore acted as protective agents for enzymes and can therefore be used as enzyme immobilizing agents. Additionally, they also acted as excellent Brönsted acid catalysts.

Yang, Kar Lai Alice. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

Philosophiae Doctor - PhD / The field of nanotechnology continues to offer solutions for biotechnologists whose target is to improve the quality of life by finding new therapies to combat diseases. Gold nanoparticles (AuNPs) have been showing great potentials in many biomedical applications. The antibacterial activity of the AuNPs presents a therapeutic option for conditions caused by bacterial infections such as chronic wounds. Also, these versatile particles can offer solutions in the treatments of infectious diseases and can also be exploited as “smart” vehicles to carry drugs, such as antibiotics, for improved efficiency. Moreover, the anti-inflammatory activity of AuNPs makes them useful in the management of prolonged inflammation caused by bacterial infections. The synthesis of AuNPs can be achieved by variety of physical and chemical methods that have been successfully applied in labs and industry. Nonetheless, the drawbacks of these “conventional” methods in terms of high cost, adverse health side effects and incompatibility with the ecosystem cannot be overlooked. Thus, new safer and more cost-effective protocols have been reported for the synthesis of AuNPs. Plants have provided alternate synthesis methods in which the reducing capabilities of the phytochemicals, found in the aqueous plant extracts, can be used to chemically synthesize AuNPs from gold precursors. The biosynthesis and characterization of AuNPs from the phytochemicals of several South African plants is investigated in this study. The study also reports the optimization of the AuNPs biosynthesis by varying reaction conditions such as temperature and plant extracts’ concentrations. Furthermore, the study highlights the wound healing activity of the AuNPs synthesized from selected plants by investigating their antibacterial activity on bacterial strains known to cause chronic wounds. The ability of these AuNPs to carry ampicillin in order to enhance the antibacterial activity is also described herein. The cytotoxicity of the biosynthesized AuNPs was evaluated on human normal fibroblasts cells (KMST-6). Additionally, the immunomodulatory effect of the biosynthesized AuNPs on the cytokines production from macrophages and Natural Killer (NK) cells was examined. The study was successful to produce biocompatible and safe AuNPs synthesized from the tested aqueous plant extracts. The resulted AuNPs showed different physicochemical properties by varying the reaction conditions. The AuNPs exhibited antibacterial activity against several Gram-positive and Gram-negative bacteria. Also, ampicillin was successfully loaded on the biosynthesized AuNPs, which led to the formation of more antibacterial active conjugated AuNPs compared to the free AuNPs. The green synthesized AuNPs were also found to have anti-inflammatory responses as shown by the reduction of pro-inflammatory cytokines from immune cells. In vitro assays showed that the biogenic AuNPs were not toxic to KMST-6 cells. Overall, the data suggest that plant extracts produce biologically safe AuNPs with antibacterial and anti-inflammatory activities that can be exploited in the treatment of chronic wounds and in the management of chronic inflammation.

Magnetic nanoparticles attract increasing attention because of their current and potential biomedical applications, such as, magnetically targeted and controlled drug delivery, magnetic hyperthermia and magnetic extraction. Increased magnetization can lead to improved performance in targeting and retention in drug delivery and a higher efficiency in biomaterials extraction. We reported an approach to synthesize iron contained magnetic nanoparticles with high magnetization and good oxidation resistibility by pyrolysis of iron pentacarbonyl (Fe(CO)[subscript 5]) in methane (CH[subscript 4]). Using the high reactivity of Fe nanoparticles, decomposition of CH[subscript 4] on the Fe nanoparticles leads to the formation of nanocrystalline iron carbides at a temperature below 260°C. Structural investigation indicated that the as-synthesized nanoparticles contained crystalline bcc Fe, iron carbides and spinel iron oxide. The Mössbauer and DSC results testified that the as-synthesized nanoparticle contained three crystalline iron carbide phases, which converted to Fe[subscript 3]C after a heat treatment. Surface analysis suggested that the as-synthesized and subsequently heated iron-iron carbide particles were coated by iron oxide, which originated from oxidization of surface Fe atoms. The heat-treated nanoparticles exhibited a magnetization of 160 emu/g, which is two times of that of currently used spinel iron oxide nanoparticles. After heating in an acidic solution with a pH value of 5 at 60°C for 20 h, the nanoparticles retained 90 percentage of the magnetization. / Singapore-MIT Alliance (SMA)

Metallic nanoparticles (NPs) with various elemental composition, size, shape and physical or chemical properties has become active field of research. Among all the metal NPs noble metal ones are receiving much attention due to their special optical properties which make them useful for different applications. Noble metal NPs have bright colors resulting from strong surface plasmon resonance absorption usually in the visible region. The colors are size and shape dependent and provide the tuning of optical properties. The optical properties of NPs are also strongly depending on the nature of the NPs surface which plays a crucial role on chemical sensing. Therefore, surface modification of NPs has become increasingly important. In this study, gold NPs were prepared in aqueous phase by seed-mediated growth method. To enhance the optical properties, surface functionalization was performed by coating NPs with silver. The coating process was achieved by chemical reduction of silver ions on NPs surface. Thickness of silver layer on the NPs were attempted to be controlled by the amount of silver salt added into NPs solution. Coating process of different types of gold NPs (rod, octahedral, star) was done by the same procedure. Moreover, this attempt yielded control over silver layer thickness on sphere, rod and octahedral shaped gold NPs, but not on branched NPs. The structure, composition and spectroscopic properties of Au-Ag core shell NPs were characterized by UV-Vis spectroscopy, Field Emission Transmission Electron Microscope (FE-TEM) and Energy-dispersive X-ray (EDX) studies, Scanning Electron Microscope (SEM), and X-Ray Photoelectron Spectroscopy (XPS). The analysis showed that all NPs studied were successfully coated with silver and promising for further explorations in sensing and imaging applications.

Alloying is an old trick used to produce new materials by synergistically combining at least two components. New developments in nanoscience have enabled new degrees of freedom, such as size, solubility and concentration of the alloying element to be utilized in the design of the physical properties of alloy nanoparticles (ANPs). ANPs as multi-functional materials have applications in catalysis, biomedical technologies and electronics. Phase diagrams of ANPs are very little known and may not represent that of bulk picture, furthermore, ANPs with different crystallite orientation and compositions could remain far from equilibrium. Here, we studied the synthesis and stability of Au-Sn and Ag-Ni ANPs with chemical reduction method at room temperature. Due to the large difference in the redox potentials of Au and Sn, co-reduction is not a reproducible method. However, two step successive reductions was found to be more reliable to generate Au-Sn ANPs which consists of forming clusters in the first step (either without capping agent or with weakly coordinated surfactant molecules) and then undergoing a second reduction step in the presence of another metal salt. Our observation also showed that capping agents (Cetrimonium bromide or (CTAB)) and Polyacrylic acid (PAA)) play a key role in the alloying process and shorter length capping agent (PAA) may facilitate the diffusion of individual components and thus enabling better alloying. Different molar ratios of Sn and Au precursors were used to study the effect of alloying elements on the melting point and the crystalline structures and melting points were determined by various microscopy and spectroscopy techniques and differential scanning calorimetry (DSC). A significant depression (up to150°C) in the melting transition was observed for the Au-Sn ANPs compared to the bulk eutectic point (T m 280°C) due to the size and shape effect. Au-Sn ANPs offer a unique set of advantages as lead-free solder material which can reflow at lower temperatures leading to lower thermal stresses in adjacent electronic components during the manufacturing process, offering better thermal and mechanical properties suitable for high temperature electronic applications. The second system studied here is Ag-Ni ANPs and electron microscopy and spectroscopy confirm the formation of Ag 0.5 Ni 0.5 ANPs with cubic structure, stable up to125°C. Atomic size and crystalline structure have less effect on the alloy formation process at the nanoscale; therefore, metals with limited solubility in bulk could form solid solutions at the nanoscale. Ag and Ni are immiscible in both solid and liquid states due to the large lattice mismatch and thermodynamically, the formation of core-shell structures is favoured. The effect of capping agents on the alloying was also studied here. Polyvinyl alcohol (PVA) with shorter length shows Ag-Ni ANPs with higher content of Ni compared to sodium citrate; the systems lead to the formation of Ag, Ag 2 O 2 and Ag 0.5 Ni 0.5 ANPs. The study of multi-component nanoparticle systems could shed light into the various parameters that affect stability of structure and phases, which could be quite distinct from their bulk counterparts.

No description available.

Metal chalcogenide nanomaterials are interesting due to their size dependent properties and potential use in numerous types of devices or applications. The synthetic methods of binary phase metal chalcogenide nanoparticles are well established, but finding simple ways to make even more complex nanostructures is important. To this end, two techniques were studied: the cation exchange of metal chalcogenide nanocrystals, CdE → MxEy (E = S, Se, Te; M = Pd, Pt) and the solution phase synthesis of ternary chalcogenide nanoparticles. The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of CdE → MxEy were investigated. A two-phase solvent environment was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes, such as void formation and fragmentation, in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guide to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals. Using a solution phase method, the morphology of CuInSe2 nanoparticles could be tuned from small 10 nm spheres to micron length nanowires by varying the relative amount of strong and weak surfactants passivating the surface. Oleylamine and trioctylphosphine oxide were chosen as the strong and weak surfactants, respectively. Small isotropic structures were formed when the oleylamine was the only surfactant with the size of the nanospheres increasing as the amount of oleylamine decreased. For the CuInSe2 nanowires, weakly-binding dioctylphosphine oxide (DOPO), an impurity in the TOPO, was found to be the key surfactant that enables the anisotropic one-dimensional growth. Detailed analysis of the structure of the nanowires indicated that they grow perpendicular to (112) planes, with twinning around the growth axis by ~60 degree rotation. The nanowires exhibit a saw-tooth surface morphology resembling a stack of truncated tetrahedral.

Polymers are with low carrier mobility. If polymer solar cells are to exhibit high power conversion efficiencies, their carrier mobilities must be improved. Metallic NPs are promising materials for use in polymer solar cells because of their high conductivities. In this work, we studied the carrier transport characteristic of metallic nanoparticle blending into polymers. We blended Pt nanoparticles (Pt NPs) and Pd nanoparticles (Pd NPs) into polymers to improve carrier mobility, and enhance the power conversion efficiency of the polymer solar cell. P3HT was used as a donor material because of its high stability and with high absorption in visible light. PCBM was used as a acceptor material because of its high stability and with high electron transportation. We blended modified Pt NPs and Pd NPs into the P3HT:PCBM active layer, with the device configurations of ITO/PEDOT:PSS/P3HT:PCBM: Pt NPs/Al and ITO/PEDOT:PSS/P3HT:PCBM:Pd NPs/Al, respectively polymer solar cells measured was under AM 1.5G 100mW/cm2 illumination. When we blended Pt NPs into the active layer, the open-circuit remained 0.64V, the short-circuit current increased from 6.67mA/cm2 to 9mA/cm2, the power conversion efficiency increased from 1.96% to 3.08%. When we blended Pd NPs into the active layer, the open-circuit remained 0.62V, the short-circuit current increased from 6.33mA/cm2 to 7.33mA/cm2, the power conversion efficiency increased from 1.7% to 2.48%. The enhanced efficiency originated from the increased carrier mobility of the active layer when the Pt NPs or Pd NPs were present.