Gold Nanoparticle: Preparation, Properties, Labeling And Catalysis Applications

In this thesis, gold nanoparticles with different size, shape and capping materials were prepared. The gold nanoparticles offered wide range of physical and chemical properties and applications. Properties such as plasmonics interaction, non-specific adsorption were studied and related to labeling strategies. Gold nanoparticle supported on solid materials acted as catalyst and allowed the exploitation and optimization of the catalysis of Sonogashira coupling and oxidation of cyclohexane reactions. For catalysis reaction, the effect of gold nanoparticles size and shape were explored.The labeling strategy with gold nanoparticles for the conventional surface plasmon resonance (SPR) signal enhancement has been frequently used for the sensitive determination of small molecules binding to its interaction partners. However the influence of gold nanoparticles with different size and shape on SPR signal is not known. In this work, three kinds of gold nanoparticles, namely nanorods, nanospheres and nanoctahedrons with different size, were used to investigate their effects on the conventional SPR signal at a fixed excitation wavelength 670 nm. It was found that the SPR signal (i.e. resonant angle shift) was varied with the shapes and sizes of gold nanoparticles in suspension at a fixed concentration due to their different plasmon absorbance bands. For gold nanorods with different longitudinal absorbance bands, three conventional SPR signal regions could be clearly observed when the gold nanorod suspensions were separately introduced onto the SPR sensorchip surface. One region was the longitudinal absorbance bands coinciding with or close to the SPR excitation wavelength that suppressed the SPR angle shift. The second region was the longitudinal absorbance bands at 624 to 639 nm and 728 to 763 nm that produced a moderate increase in the SPR resonant angle shift. The third region was found for the longitudinal absorbance bands from 700 nm to 726 nm that resulted in a remarkable increase in the SPR angle shift responses. This phenomenon can be explained on the basis of calculation of the correlation of SPR angle shift response with the gold nanorod longitudinal absorbance bands. For nanospheres and nanoctahedrons, the SPR angle shift responses were found to be particle shape- and size-dependent in a simple way with a sustaining increase when the sizes of the nanoparticles were increased. Consequently, a guideline for choosing gold nanoparticles as tags is suggested for the SPR determination of small molecules with binding to the immobilized interaction partners.Relating to labelling strategies is the controlling of the non-specific adsorption of the gold nanoparticle labels to the analytic target. It is crucial in a successful investigation of the specific ligand-target binding interaction. This work presents the investigation of the adsorption properties of gold nanoparticles with superficially tethered ferrocene functions to different surfaces. The gold nanoparticles were coated with a mixed monolayer of PEG-thiol and progargyl PEG-thiol, and the later was linked with a ferrocene moiety (Fc) through the progargyl-azide click reaction. The adsorption behaviour of the Fc-gold nanoparticle to glassy carbon, gold and platinum electrodes, in the absence and presence of a self assembled monolayer (SAM) or protein layer, were studied by cyclic voltammetry (CV). It was found that the bare gold electrode possessed higher adsorption capacity. However, the adsorption was either reduced or completely prevented when the gold electrode was modified with monolayers of 2-mercaptoethanol (ME), dodecanethiolate (DT) and PEG-thiol. The electroactive and water dispersible gold nanoparticles with ferrocene labels allow us to use CV to explore the interaction between these gold nanoparticles and bovine serum albumin (BSA). The BSA modified electrode resulted in better resistant to adsorption compared to other modifiers coated electrodes. Thus, the study of non-specific adsorption by CV was found effective when compared to results obtained by surface plasmon resonance (SPR) and Fourier Transform Infrared (FTIR).Catalysis by gold nanoparticle is an increasingly popular field. Catalyzed Sonogashira coupling is widely studied under various catalysts. In this research work, gold nanocatalysts with a series of shape, size and capping agent were prepared by adsorption of preformed nanoparticles on lanthana and characterized by TEM and tested for the catalysis of Sonogashira coupling reaction of phenylacetylene and iodobenzene at various reaction temperatures. When the coupling reaction performed under microwave irradiation in DMF resulted in the formation of the desired DPA in excellent yield. Importantly the results of catalyzed reaction with nanocatalysts with various shape and size undoubtedly indicated a pronounced shape and size dependent on the coupling reaction. The spherical supported gold nanoparticle was found to be the most effective catalyst. However, a remarkable loss of activity was observed in the second run, resulting only in a 34% yield. The stability of gold nanoparticle on the gold support was found to be a significant factor in the catalysis of Sonogashira reaction and the surface atoms.The second catalysis reaction included in this work is the oxidation of cyclohexane. The development of an efficient catalytic system for the oxidation of cyclohexane is a subject of great importance both from an economic and environmental point of view. Herein the oxidation of cyclohexane was performed using various gold nanocatalysts supported on lanthana under conventional heating system, sonication, and microwave irradiation. The reactions were conducted in solvent and solvent free systems in presence of radical initiator. The nanocatalysts were prepared by deposition-precipitation and adsorption of preformed gold nanoparticle methods. Thus spherical, hexagonal, and PEGylated gold nanoparticles with diameters ranging from 4 to 56 nm were used for oxidation of cyclohexane. This category of gold nanoparticle catalysts has never been explored for the oxidation of cyclohexane. Most of these gold nanocatalysts resulted in reasonable oxidation of cyclohexane. Near 11% conversion of cyclohexane was achieved on spherical and hexagonal gold catalyst with 4 and 56 nm diameters respectively. In addition, the spherical gold nanoparticle catalyst was recyclable for the titled reaction system. For all catalysis systems, the oxidation of cyclohexane was found effective when performed in solvent free and under microwave irradiation. The ease with which pre-catalyst of this system can be prepared, combined with their efficiency, recyclability and environmentally attractive process, makes these gold nanoparticles an attractive alternative catalyst.