Water-dispersible nanoparticles via interdigitation of sodium dodecylsulphate molecules in octadecylamine-capped gold nanoparticles at a liquid-liquid interface

This paper describes the formation of water-dispersible gold nano-particles capped with a bilayer of sodium dodecylsulphate (SDS) and octadecylamine (ODA) molecules. Vigorous shaking of abiphasic mixture consisting of ODA-capped gold nanoparticles in chloroform and SDS in water results in the rapid phase transfer of ODA-capped gold nanoparticles from the organic to the aqueous phase, the latter acquiring a pink, foam-like appearance in the process. Drying of the coloured aqueous phase results in the formation of a highly stable, reddish powder of gold nanoparticles that may be readily redispersed in water. The water-dispersible gold nanoparticles have been investigated by UV-Vis spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). These studies indicate the presence of interdigitated bilayers consisting of an ODA primary monolayer directly coordinated to the gold nanoparticle surface and a secondary monolayer of SDS, this secondary monolayer providing sufficient hydrophilicity to facilitate gold nanoparticle transfer into water and rendering them water-dispersible

Use of aqueous foams for the synthesis of gold nanoparticles of variable morphology

In this paper we describe the facile synthesis of gold nanocrystals of variable morphology using aqueous foam as a template. The aqueous foams are formed by bubbling an aqueous solution of AuCl−4 ions electrostatically complexed with the surfactant cetyltrimethylammonium bromide (CTAB). The gold ions in the stable foam are then reduced by hydrazine vapours, this process leading to the formation of gold nanoparticles of spherical, flat plate and flake-like structures. The variation in morphology of the gold nanoparticles derived from the foam is believed to arise from the complex spatial structure of reaction sites in the foam. The foam-derived gold nanoparticles were analysed by UV-vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy

New approach towards imaging λ-DNA using scanning tunneling microscopy/spectroscopy (STM/STS)

A new methodology to anchor λ-DNA to silanized n-Si(111) surface using Langmuir Blodget trough was developed. The n-Si (111) was silanized by treating it with low molecular weight octyltrichlorosilane in toluene. Scanning tunneling microscopy (STM) image of λ-DNA on octyltrichlorosilane deposited Si substrate shows areas exhibiting arrayed structures of 700 nm length and 40 nm spacing. Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of n-Si(111) which presumably facilitates tunneling through otherwise insulating DNA layer

Phase transfer of platinum nanoparticles from aqueous to organic solutions using fatty amine molecules

In this report we demonstrate a simple process based on amine chemistry for the phase transfer of platinum nanoparticles from an aqueous to an organic solution. The phase transfer was accomplished by vigorous shaking of a biphasic mixture of platinum nanoparticles synthesised in an aqueous medium and octadecylamine (ODA) in hexane. During shaking of the biphasic mixture, the aqueous platinum nanoparticles complex via either coordination bond formation or weak covalent interaction with the ODA molecules present in the organic phase. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilised platinum nanoparticles could be separated out from hexane in the form of a powder that is readily redispersible in weakly polar and non-polar organic solvents. The ODA-capped platinum nanoparticles show high catalytic activity in hydrogenation reactions and this is demonstrated in the efficient conversion of styrene to ethyl benzene. The nature of binding of the ODA molecules to the platinum nanoparticles surface was characterised by thermogravimetry, transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR)

New approach towards imaging λ-DNA using scanning tunneling microscopy/spectroscopy (STM/STS)

Abstract. A new methodology to anchor λ-DNA to silanized n-Si(111) surface using Langmuir Blodget trough was developed. The n-Si (111) was silanized by treating it with low molecular weight octyltrichlorosilane in toluene. Scanning tunneling microscopy (STM) image of λ-DNA on octyltrichlorosilane deposited Si substrate shows areas exhibiting arrayed structures of 700 nm length and 40 nm spacing. Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of nSi(111) which presumably facilitates tunneling through otherwise insulating DNA layer

Biological synthesis of strontium carbonate crystals using the fungus Fusarium oxysporum

The total biological synthesis of SrCO3 crystals of needlelike morphology arranged into higher order quasi-linear superstructures by challenging microorganisms such as fungi with aqueous Sr2+ ions is described. We term this procedure "total biological synthesis" since the source of carbonate ions that react with aqueous Sr2+ ions is the fungus itself. We believe that secretion of proteins during growth of the fungus Fusarium oxysporum is responsible for modulating the morphology of strontianite crystals and directing their hierarchical assembly into higher order superstructures

Aqueous foams as templates for the synthesis of calcite crystal assemblies of spherical morphology

The crystallization of calcite in the form of spheroaggregates in aqueous foam stabilized by the surfactant sodium bis-2-ethylhexyl-sulfosuccinate (aerosol OT, AOT) by a method of ion entrapment is described. Reaction of Na2CO3 with Ca2+ ions electrostatically entrapped in the foam results in the formation of flat, platelike calcite crystals, possibly in the plateau border regions of the foam. Hydrodynamic flow patterns in the foam are believed to transport the calcite platelets from the plateau border regions into the larger plateau junctions where they assemble into spherical structures by hydrophobic association. The large interfacial area of the liquid lamellae in the foam provides an attractive and versatile template for the large-scale synthesis of not only minerals but also other nanoscale materials