A New Technique for the Spontaneous Growth of Colloidal Nanoparticle Superlattices

The spontaneous growth of thin films of carboxylic acid derivatized colloidal gold particles electrostatically immobilized at the hydrosol−organic solution interface onto moistened hydrophilic substrates is demonstrated. Immersion of the substrates up to the interface of the biphasic mixture leads to superlattice formation by an extremely fast climbing mechanism, the process apparently driven by surface tension gradients at the substrate surface (Marangoni growth). This approach shows promise for development in the deposition of superlattice films of different surface-modified colloidal nanoparticles as well as salts of fatty lipids

Fungus-Mediated Biotransformation of Amorphous Silica in Rice Husk to Nanocrystalline Silica

Rice husk is a cheap agro-based waste material, which harbors a substantial amount of silica in the form of amorphous hydrated silica grains. However, there have been no attempts at harnessing the enormous amount of amorphous silica present in rice husk and its room-temperature biotransformation into crystalline silica nanoparticles. In this study, we address this issue and describe how naturally deposited amorphous biosilica in rice husk can be bioleached and simultaneously biotransformed into high value crystalline silica nanoparticles. We show here that the fungus Fusarium oxysporum rapidly biotransforms the naturally occurring amorphous plant biosilica into crystalline silica and leach out silica extracellularly at room temperature in the form of 2−6 nm quasi-spherical, highly crystalline silica nanoparticles capped by stabilizing proteins; that the nanoparticles are released into solution is an advantage of this process with significant application and commercial potential. Calcination of the silica nanoparticles leads to loss of occluded protein and to an apparently porous structure often of cubic morphology. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential cheap agro-industrial waste materials is an exciting possibility and could lead to an energy-conserving and economically viable green approach toward the large-scale synthesis of oxide nanomaterials

Intercolloidal Particle Monolayer Transfer in Mixed Metal Colloids

In this paper, we provide the first evidence that suggests transfer of molecules in self-assembled monolayers between colloidal metal particles. This was studied by capping silver/gold colloidal particles with a bifunctional molecule, 4-carboxythiophenol, and then mixing to the capped sol, uncapped colloidal particles of gold/silver. The transfer of the capping molecule to the bare metal particle surface leads to carboxylic acid derivatization of the uncapped sol as well. The resulting carboxylic acid derivatization of the uncapped clusters by intercolloidal particle monolayer transfer was determined by electrostatic complexation of the clusters in the mixed hydrosol at the air−water interface with a Langmuir monolayer of octadecylamine, the carboxylic acid groups playing the role of sticky “tracers”. Optical absorption spectroscopy and energy dispersive analysis of X-rays measurements of Langmuir−Blodgett films formed from subphases of sols of capped silver/gold mixed with uncapped gold/silver revealed the presence of both silver and gold particles in the film thereby pointing to the transfer of molecules between the colloidal particles. Possible mechanisms for the intercolloidal particle monolayer transfer observed are briefly discussed

Biosynthesis of CaCO₃ Crystals of Complex Morphology Using a Fungus and an Actinomycete

The biosynthesis of CaCO3 by reaction of aqueous Ca2+ ions with a fungus, Fusarium sp., and an actinomycete, Rhodococcus sp. (both plant organisms), is described. In the case of the fungus, cruciform-shaped calcite crystals are obtained (SEM picture A) while the actinomycete yielded the unstable polymorph of CaCO3, vaterite (SEM picture B). Specific proteins secreted by the microorganisms are responsible for the morphology and crystallography control observed. A highlight of this approach is that the microorganisms also provide CO2 for reaction with the Ca2+ ions, making the crystals completely biogenic

Role of Particle Size in Individual and Competitive Diffusion of Carboxylic Acid Derivatized Colloidal Gold Particles in Thermally Evaporated Fatty Amine Films

We have recently shown that nanocomposites of colloidal particles in a fatty lipid matrix can be grown via a diffusion process controlled by selective electrostatic interactions. In this paper, a detailed investigation of the diffusion of carboxylic acid derivatized gold colloidal particles of different sizes into thermally evaporated octadecylamine films using quartz crystal microgravimetry (QCM), transmission electron microscopy, and UV−vis absorption and Fourier transform infrared (FTIR) spectroscopies is described. The QCM kinetics of gold cluster incorporation has been analyzed in terms of a one-dimensional Fickian-type diffusion model, and it is found that the cluster diffusivity increases with decreasing cluster size. The pH at which maximum cluster incorporation in the amine occurs was found to be dependent on the cluster size as well. FTIR spectroscopy of the fatty amine-gold particle composites indicated weak coupling of the clusters to the protonated amine groups as well as interesting cluster size dependent changes in the amine and methylene antisymmetric deformations as well as the methylene scissoring bands. In a competitive diffusion process of large and small gold particles, it was observed that bigger gold particles were preferentially incorporated into the amine matrix even though the cluster diffusivity is higher for the smaller gold particles

Photoinduced Stitching of Self-Assembled Triangular Silver Nanoprisms at the Air–Water Interface

This study investigates the influence of optical excitation on the self-assembly of triangular nanoprisms of silver into a continuous monolayer at the air–water interface. Langmuir monolayers of octadecylamine (ODA) have been used to electrostatically assemble citrate-capped silver triangular nanoprisms (AgTNPs) in the presence and absence of light. Under optical excitation, the nanoprisms were observed to assemble into a well-ordered monolayer through plasmon-mediated stitching, whereas the particles were merely in close contact during assembly in the dark. These findings suggest new avenues for tailoring particle properties through light-mediated assembly in two dimensions

Biosynthesis of CaCO₃ Crystals of Complex Morphology Using a Fungus and an Actinomycete

The biosynthesis of CaCO3 by reaction of aqueous Ca2+ ions with a fungus, Fusarium sp., and an actinomycete, Rhodococcus sp. (both plant organisms), is described. In the case of the fungus, cruciform-shaped calcite crystals are obtained (SEM picture A) while the actinomycete yielded the unstable polymorph of CaCO3, vaterite (SEM picture B). Specific proteins secreted by the microorganisms are responsible for the morphology and crystallography control observed. A highlight of this approach is that the microorganisms also provide CO2 for reaction with the Ca2+ ions, making the crystals completely biogenic

Data_Sheet_1_Size and Shape Directed Novel Green Synthesis of Plasmonic Nanoparticles Using Bacterial Metabolites and Their Anticancer Effects.PDF

The growing need for developing new synthesis methods of plasmonic nanoparticles (PNPs) stems from their various applications in nanotechnology. As a result, a variety of protocols have been developed for the synthesis of PNPs of different shapes, sizes, and compositions. Though widely practiced, the chemical synthesis of PNPs demands stringent control over the experimental conditions, often employs environmentally hazardous chemicals for surface stabilization, and is frequently energy-intensive. Additionally, chemically obtained PNPs require subsequent surface engineering steps for various optoelectronic and biomedicine applications to minimize the toxic effects and render them useful for targeted drug delivery, sensing, and imaging. Considering the pressing need to develop environmentally-friendly technology solutions, “greener” methods of nanoparticle synthesis are gaining importance. Here, we report on the biological synthesis of plasmonic nanoparticles using bacterial metabolites. A peptide-based siderophore pyoverdine and a blue-green pigment pyocyanin obtained from a marine strain of Pseudomonas aeruginosa rapidly produced plasmonic nanoparticles of gold and silver in an aqueous environment. The morphology of plasmonic nanoparticles could be modulated by tuning the concentration of these metabolites and the reaction time. The exposure of pyoverdine to chloroauric acid resulted in anisotropic gold nanoparticles. On the other hand, pyocyanin produced a highly monodispersed population of gold nanoparticles and anisotropic silver nanoparticles. Biologically obtained gold and silver nanoparticles retained pyoverdine and pyocyanin on the nanoparticle surface and were stable for an extended period of time. The biologically obtained gold and silver plasmonic nanoparticles displayed potent anticancer activities against metastatic lung cancer cells. Biogenic nanoparticles were rapidly internalized by cancer cells in high quantity to affect the cellular organization, and karyoplasmic ratio, indicating the potential of these nanoparticles for cancer nanomedicine.</p

Synthesis of Hydroxyapatite Crystals Using Amino Acid-Capped Gold Nanoparticles as a Scaffold

Inorganic composites are of special interest for biomedical applications such as in dental and bone implants wherein the ability to modulate the morphology and size of the inorganic crystals is important. One interesting possibility to control the size of inorganic crystals is to grow them on nanoparticles. We report here the use of surface-modified gold nanoparticles as templates for the growth of hydroxyapatite crystals. Crystal growth is promoted by a monolayer of aspartic acid bound to the surface of the gold nanoparticles; the carboxylate ions in aspartic acid are excellent binging sites for Ca2+ ions. Isothermal titration calorimetry studies of Ca2+ ion binding with aspartic acid-capped gold nanoparticles indicates that the process is entropically driven and that screening of the negative charge by the metal ions leads to their aggregation. The aggregates of gold nanoparticles are believed to be responsible for assembly of the platelike hydroxyapatite crystals into quasi-spherical superstructures. Control experiments using uncapped gold nanoparticles and pure aspartic acid indicate that the amino acid bound to the nanogold surface plays a key role in inducing and directing hydroxyapatite crystal growth

Photoinduced Stitching of Self-Assembled Triangular Silver Nanoprisms at the Air–Water Interface

This study investigates the influence of optical excitation on the self-assembly of triangular nanoprisms of silver into a continuous monolayer at the air–water interface. Langmuir monolayers of octadecylamine (ODA) have been used to electrostatically assemble citrate-capped silver triangular nanoprisms (AgTNPs) in the presence and absence of light. Under optical excitation, the nanoprisms were observed to assemble into a well-ordered monolayer through plasmon-mediated stitching, whereas the particles were merely in close contact during assembly in the dark. These findings suggest new avenues for tailoring particle properties through light-mediated assembly in two dimensions