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.

Immobilization of biogenic gold nanoparticles in thermally evaporated fatty acid and amine thin films

We have recently demonstrated the biological synthesis of gold nanoparticles by the reduction of aqueous chloroaurate ions by the fungus Fusarium oxysporum and with extract of geranium (Pelargonium graveolens) leaf. In this paper, we demonstrate the immobilization of biogenic gold nanoparticles in lipid thin films deposited by thermal evaporation. The charge on the gold nanoparticles synthesized by both the fungus and the geranium plant extract is used to facilitate their immobilization in both anionic and cationic lipid thin films. A rough estimate of the isoelectric point of the proteins capping the gold nanoparticles synthesized using the fungus could be made by pH-dependent microgravimetry studies of the immobilization process. An interesting size and shape selectivity in the immobilized gold nanoparticles is observed in the lipid thin films. The biogenic gold nanoparticle-lipid composite films were characterized using quartz crystal microgravimetry, UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy.

Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth

We report on the use of Neem (Azadirachta indica) leaf broth in the extracellular synthesis of pure metallic silver and gold nanoparticles and bimetallic Au/Ag nanoparticles. On treatment of aqueous solutions of silver nitrate and chloroauric acid with Neem leaf extract, the rapid formation of stable silver and gold nanoparticles at high concentrations is observed to occur. The silver and gold nanoparticles are polydisperse, with a large percentage of gold particles exhibiting an interesting flat, platelike morphology. Competitive reduction of Au3+ and Ag+ ions present simultaneously in solution during exposure to Neem leaf extract leads to the synthesis of bimetallic Au core-Ag shell nanoparticles in solution. Transmission electron microscopy revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core-shell structure. The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in our earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.

Biological synthesis of triangular gold nanoprisms

The optoelectronic and physicochemical properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chemical methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the extract from the lemongrass plant, when reacted with aqueous chloroaurate ions, yields a high percentage of thin, flat, single-crystalline gold nanotriangles. The nanotriangles seem to grow by a process involving rapid reduction, assembly and room-temperature sintering of 'liquid-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-infrared absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.

Free-standing nanogold membranes as scaffolds for enzyme immobilization

We demonstrate herein the formation of a free-standing gold nanoparticle membrane and its use in the immobilization of the enzyme, pepsin. The nanogold membrane is synthesized by the spontaneous reduction of aqueous chloroaurate ions at the liquid-liquid interface by the bifunctional molecule bis(2-(4-aminophenoxy)ethyl) ether (DAEE) taken in chloroform. This process results in the formation of a robust, malleable free-standing nanogold membrane consisting of gold nanoparticles embedded in a polymeric background. Recognizing that gold nanoparticles are excellent candidates for immobilization of enzymes, we have immobilized pepsin on the nanogold membrane, leading to a new class of biocatalyst. A highlight of the new pepsin-nanogold biocatalyst is the ease with which separation from the reaction medium may be achieved. The catalytic activity of pepsin in the bioconjugate was comparable to that of the free enzyme in solution. The pepsin-nanogold membrane bioconjugate material exhibited excellent biocatalytic activity over 10 successive reuse cycles as well as enhanced pH, temperature, and temporal stability.

Formation of platinum nanoparticles at air–water interfaces by the spontaneous reduction of subphase chloroplatinate anions by hexadecylaniline Langmuir monolayers

The one-step electrostatic complexation, reduction of aqueous chloroplatinate ions, and capping of the platinum nanoparticles thus formed by hexadecylaniline Langmuir monolayers is described. The capping of the platinum nanoparticles formed spontaneously at the air-water interface by hexadecylaniline enables their facile transfer as multilayers onto suitable solid substrates by the Langmuir-Blodgett technique. The real-time reduction of the aqueous chloroplatinate ions at the air-water interface was followed by measurement of the pressure-area isotherms, while the multilayer Langmuir-Blodgett films were characterized by quartz crystal microgravimetry, transmission electron microscopy, electron diffraction, and X-ray photoemission spectroscopy.

Water-dispersible tryptophan-protected gold nanoparticles prepared by the spontaneous reduction of aqueous chloroaurate ions by the amino acid

The synthesis of water-dispersible amino-acid-protected gold nanoparticles by the spontaneous reduction of aqueous chloroaurate ions by tryptophan is described. Water-dispersible gold nanoparticles may also be obtained by the sequential synthesis of the gold nanoparticles by borohydride reduction of chloroauric acid followed by capping with tryptophan. Comparison of the proton NMR spectroscopic signatures from the tryptophan-protected gold nanoparticles obtained by the two processes indicated that the indole group in tryptophan is responsible for reduction of the aqueous chloroaurate ions. The reduction of the metal ions is accompanied by oxidative polymerization of the indole group of the tryptophan molecules and, consequently, some degree of cross-linking of the gold nanoparticles.

Immobilization and biocatalytic activity of fungal protease on gold nanoparticle-loaded zeolite microspheres

Gold nanoparticles are excellent biocompatible surfaces for the immobilization of enzymes. However, separation of the gold nanoparticle-enzyme bioconjugate material from the reaction medium is often difficult. In this study, we investigate the assembly of the gold nanoparticles on the surface of the amine-functionalized zeolite microspheres in the formation of zeolite-gold nanoparticle "core-shell" structures and, thereafter, the use of this structure in immobilization of fungal protease. The assembly of gold nanoparticles on the zeolite surface occurs through the amine groups present in 3-aminopropyltrimethoxysilane (3-APTS). The fungal proteases bound to the massive "core-shell" structures were easily separated from the reaction medium by mild centrifugation and exhibited excellent reuse characteristics. The biocatalytic activity of fungal protease in the bioconjugate was marginally enhanced relative to the free enzyme in solution. The bioconjugate material also showed significantly enhanced pH and temperature stability and a shift in the optimum temperature of operation.

A low-temperature, soft chemistry method for the synthesis of zirconia nanoparticles in thermally evaporated fatty amine thin films

We demonstrate the synthesis of zirconia nanoparticles in a lipid matrix by a simple, low temperature beaker-based process. This is accomplished by electrostatic entrapment of ZrF6(2-) ions within thermally evaporated octadecylamine (ODA) thin films followed by the low-temperature in situ hydrolysis of the entrapped metal ion complexes. The zirconia particles thus formed were of the monoclinic phase and were fairly monodisperse with particles of average size 40 nm. The zirconia crystallites appeared to exhibit preferred orientation indicating epitaxial growth of the crystals within the lipid matrix. The formation of zirconia nanoparticles in the lipid matrix was investigated using quartz crystal microgravimetry (QCM), optical absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques.

Candida bombicola Cells Immobilized on Patterned Lipid Films as Enzyme Sources for the Transformation of Arachidonic Acid to 20-HETE

Preparation of biocompatible surfaces for immobilization of enzymes and whole cells is an important aspect of biotechnology due to their potential applications in biocatalysis, biosensing, and immunological applications. In this report, patterned thermally evaporated octadecylamine (ODA) films are used for the immobilization of Candida bombicola cells. The attachment of the cells to the ODA film surface occurs possibly through nonspecific interactions such as hydrophobic interactions between the cell walls and the ODA molecules. The enzyme cytochrome P450 present in the immobilized yeast cells on the ODA film surface was used for the transformation of the arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE). The assembly of cells on the hydrophobic ODA surface was confirmed by quartz crystal microgravimetry (QCM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). SEM images confirmed the strong binding of the yeast cells to the ODA film surface after biocatalytic reactions. Moreover, the biocomposite films could be easily separated from the reaction medium and reused.

Biosynthesis of CaCO3Crystals 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.

Geranium leaf assisted biosynthesis of silver nanoparticles

Development of biologically inspired experimental processes for the synthesis of nanoparticles is evolving into an important branch of nanotechnology. In this paper, we report on the use of Geranium (Pelargonium graveolens) leaf extract in the extracellular synthesis of silver nanoparticles. On treating aqueous silver nitrate solution with geranium leaf extract, rapid reduction of the silver ions is observed leading to the formation of highly stable, crystalline silver nanoparticles in solution. Transmission electron microscopy analysis of the silver particles indicated that they ranged in size from 16 to 40 nm and were assembled in solution into quasilinear superstructures. The rate of reduction of the silver ions by the geranium leaf extract is faster than that observed by us in an earlier study using a fungus, Fusarium oxysporum, thus highlighting the possibility that nanoparticle biosynthesis methodologies will achieve rates of synthesis comparable to those of chemical methods. This study also represents an important advance in the use of plants over microorganisms in the biosynthesis of metal nanoparticles.

A new method for the synthesis of hydrophobic gold nanotapes

Protocols for the synthesis of gold nanoparticles are increasingly focusing on controlling the morphology of the nanocrystals. We demonstrate in this article the facile, one-step synthesis of gold nanotapes that are readily dispersible in organic media. This is accomplished by the spontaneous reduction of aqueous chloroaurate ions by hexadecylaniline molecules present in chloroform at the static interface between water and chloroform. The hexadecylaniline molecules cap the gold nanotapes thus formed, rendering them hydrophobic and dispersible in a range on nonpolar and weakly polar organic solvents. Possible reasons for the growth of gold nanotapes are discussed.

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

We demonstrate the phase transfer of silver nanoparticles synthesized in an aqueous medium into hexane containing the cationic surfactant octadecylamine (ODA). During vigorous shaking of the biphasic mixture, rapid phase transfer of the silver nanoparticles into the organic phase was observed. The phase transfer of the silver nanoparticles arises due to coupling of the silver nanoparticles with the ODA molecules present in organic phase via either coordination bond formation or weak covalent interaction. This process renders the nanoparticles sufficiently hydrophobic and dispersible in the organic phase. The ODA-stabilized silver nanoparticles could be separated out from the organic phase in the form of a powder and are readily redispersible in different organic solvents. The nature of binding of the ODA molecules to the silver nanoparticle surface was characterized using UV-vis spectroscopy, thermogravimetry, transmission electron microscopy, nuclear magnetic resonance spectroscopy, X-ray photoemission spectroscopy, and Fourier transform infrared spectroscopy.