Vipul Bansal

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Abstract: We show for the first time that by controlling the growth kinetics of Morganella psychrotolerans, a silver-resistant psychrophilic bacterium, the shape anisotropy of silver nanoparticles can be achieved. This is particularly important considering that there has been no report that demonstrates a control over shape of Ag nanoparticles by controlling the growth kinetics of bacteria during biological synthesis. Additionally, we have for the first time performed electrochemistry experiments on bacterial cells after exposing them to Ag ⁺ ions, which provide significant new insights about mechanistic aspects of Ag reduction by bacteria. The possibility to achieve nanoparticle shape control by using a "green" biosynthesis approach is expected to open up new exciting avenues for eco-friendly, large-scale, and economically viable shape-controlled synthesis of nanomaterials. © 2010 American Chemical Society.

Abstract: We report an unusual behavior observed in (BiFeO₃)_1-x-(PbTiO₃)_x (BF-xPT) thin films prepared using a multilayer chemical solution deposition method. Films of different compositions were grown by depositing several bilayers of BF and PT precursors of varying BF and PT layer thicknesses followed by heat treatment in air. X-ray diffraction showed that samples of all compositions show mixing of two compounds resulting in a single-phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk compositions, samples show a monoclinic (M_A-type) structure suggesting disappearance of the morphotropic phase boundary (MPB) at x=0.30 as observed in the bulk. This is accompanied by the lack of any enhancement of the remanent polarization at the MPB, as shown by the ferroelectric measurements. Magnetic measurements showed an increase in the magnetization of the samples with increasing BF content. Significant magnetization in the samples indicates melting of spin spirals in the BF-xPT films, arising from a random distribution of iron atoms. Absence of Fe²⁺ ions was corroborated by X-ray photoelectron spectroscopy measurements. The results illustrate that thin film processing methodology significantly changes the structural evolution, in contrast to predictions from the equilibrium phase diagram, besides modifying the functional characteristics of the BP-xPT system dramatically. © 2010 Springer-Verlag.

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Abstract: We demonstrate an unusual shape transformation of Ag nanospheres into {111}-oriented Au-Ag dendritic nanostructures by a galvanic replacement reaction in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). © 2010 The Royal Society of Chemistry.

Abstract: The electrochemical and electrocatalytic behaviour of silver nanoprisms, nanospheres and nanocubes of comparable size in an alkaline medium have been investigated to ascertain the shape dependent behaviour of silver nanoparticles, which are an extensively studied nanomaterial. The nanomaterials were synthesised using chemical methods and characterised with UV-visible spectroscopy, transmission electron microscopy and X-ray diffraction. The nanomaterials were immobilised on a substrate glassy carbon electrode and characterised by cyclic voltammetry for their surface oxide electrochemistry. The electrocatalytic oxidation of hydrazine and formaldehyde and the reduction of hydrogen peroxide were studied by performing cyclic voltammetric and chronoamperometric experiments for both the nanomaterials and a smooth polycrystalline macrosized silver electrode. In all cases the nanomaterials showed enhanced electrocatalytic activity over the macro-silver electrode. Significantly, the silver nanoprisms that are rich in hcp lamellar defects showed greater activity than nanospheres and nanocubes for all reactions studied. © 2010 The Royal Society of Chemistry.

Abstract: Most of the self-assembly studies have hitherto explored the aqueous media as fluid phase for self-assembly of amphiphilic biomacromolecules, wherein architectural modification of biomolecules is generally a prerequisite for self-assembly of modified biomolecules. We demonstrate for the first time that ionic liquids can act as nonaqueous designer solvents to self-assemble amphiphilic biomacromolecules without requiring their prior modification. To this end, we show that enzyme (phytase) molecules self-assembled in the presence of an appropriate ionic liquid, resulting in the formation of enzyme capsules. Phytase capsules synthesized using this approach were further used as templating nanoreactors for the synthesis of enzyme-containing hollow silica nanocontainers. In situ immobilized phytase enzyme in the silica nanocontainers, when subjected to enzyme-reusability application, establishes them as excellent reusable biocatalysts. © 2010 American Chemical Society.

Abstract: We have prepared thin films of BiFe_1-xZr_xO ₃ (x=0.0-0.15) by chemical solution deposition on Pt/Si substrates. Structural characterization of the films using x-ray diffraction and Raman spectroscopy suggests lattice distortion upon doping for x<0.15. This also appears to be the limit for pure phase formation. Ferroelectric measurements reveal that Zr doping leads to reduction in the remnant polarization and an increase in the coercive field, attributed to lattice distortion. Dielectric measurements indicate that the doped compositions exhibit absence of low frequency relaxation, usually associated with defects and grain boundaries. Absence of Fe²⁺ in our films was verified using x-ray photoelectron spectroscopy. Role of Zr in controlling the film's properties has been explained in terms of changes in the bond strength. © 2010 American Institute of Physics.

Abstract: Electrochemical studies of the salts [cat]₄[Pt ₂(μ-pop)₄] (cat⁺ = Bu₄N ⁺ or PPN⁺ [Ph₃P=N=PPh₃]⁺; pop = pyrophosphite, [P₂O₅H₂]^2-) have been carried out in dichloromethane. In agreement with published studies of K₄[Pt₂(μ-pop)₄] in water and [Ph ₄As]₄[Pt₂(μ-pop)₄] in acetonitrile, the [Pt₂(μ-pop)₄]^4- anion is found to undergo an initial one-electron oxidation under conditions of cyclic voltammetry to a short-lived trianion, [Pt₂(μ-pop) ₄]^3-. However, in the more weakly coordinating solvent dichloromethane, [Pt₂(μ-pop)₄]^3- appears to undergo oligomerization instead of solvent-induced disproportionation; thus the overall process remains a one-electron reaction rather than an overall two-electron oxidative addition process, even under long time-scale, bulk electrolysis conditions. Chemical oxidation of [cat]₄[Pt ₂(μ-pop)₄] with [NO][BF₄] or AgBF ₄ gives mainly a dark, insoluble, ill-defined solid that appears to contain Pt(III) according to X-ray photoelectron spectroscopy (XPS). In the case of [NO][BF₄], a second reaction product, an orange solid, has been identified as a nitrosyl complex, [cat]₃[Pt₂(μ-pop) ₄(NO)]. The X-ray structure of the PPN⁺ salt shows the anion to consist of the usual lantern-shaped Pt₂(μ-pop) ₄ framework with an unusually large Pt-Pt separation [2.8375(6) Ã…]; one of the platinum atoms carries a bent nitrosyl group [r(N-O) = 1.111(15) Ã…; (Pt-N-O) = 118.1(12)°] occupying an axial position. The nitrosyl group migrates rapidly on the ³¹P NMR time-scale between the metal atoms at room temperature but the motion is slow enough at 183 K that the expected two pairs of inequivalent phosphorus nuclei can be observed. The X-ray photoelectron (XP) spectrum of the nitrosyl-containing anion confirms the presence of two inequivalent platinum atoms whose 4f_7/2 binding energies are in the ranges expected for Pt(II) and Pt(III); an alternative interpretation is that the second platinum atom has a formal oxidation number of +4 and that its binding energy is modified by the strongly σ-donating NO^- ligand. Reduction of [Pt₂(μ-pop)₄X ₂]^4- (X = Cl, Br, I) in dichloromethane corresponds to a chemically reversible, electrochemically irreversible two-electron process involving loss of halide and formation of [Pt₂(μ-pop) ₄]^4-, as is the case in more strongly coordinating solvents. © 2009 American Chemical Society.

Abstract: With the increasing popularity of the galvanic replacement approach towards the development of bimetallic nanocatalysts, special emphasis has been focused on minimizing the use of expensive metal (e.g. Pt), in the finally formed nanomaterials (e.g. Ag/Pt system as a possible catalyst for fuel cells). However, the complete removal of the less active sacrificial template is generally not achieved during galvanic replacement, and its residual presence may significantly impact on the electrocatalytic properties of the final material. Here, we investigate the hydrogen evolution reaction (HER) activity of Ag nanocubes replaced with different amounts of Pt, and demonstrate how the bimetallic composition significantly affects the activity of the alloyed nanomaterial. © 2009 Elsevier B.V. All rights reserved.

Abstract: We demonstrate a simple electrochemical route to produce uniformly sized gold nanospikes without the need for a capping agent or prior modification of the electrode surface, which are predominantly oriented in the {111} crystal plane and exhibit promising electrocatalytic and SERS properties. © 2009 The Royal Society of Chemistry.

Abstract: We have investigated the formation of highly porous nanostructured tungsten trioxide (WO₃) films of several microns thickness using elevated temperature anodization in nitric acid. Plate-like crystals with thicknesses in the range of 20-60 nm and lengths in the order of 50-1000 nm were obtained after anodization of tungsten foil in 1.5 M HNO₃ at 50 °C. High intensity {2 0 0} WO₃ crystallographic signatures from platelets revealed the presence of predominantly orthorhombic WO₃ nanoplatelets in annealed (up to 550 °C) samples. Photocurrent measurements revealed that 4 h anodized sample at 20 V produced the largest photocurrent density. High photocurrent response from the nanoplateleted films show the possibility of developing efficient WO₃/electrolyte sandwiched photosensors. Crown Copyright © 2009.

Abstract: Anodization at elevated temperatures in nitric acid has been used for the production of highly porous and thick tungsten trioxide nano structured films for photosensitive device applications. The anodization process resulted in platelet crystals with thicknesses of 20-60 nm and lengths of 100-1000 nm. Maximum thicknesses of ∼2.4 μm were obtained after 4 h of anodization at 20 V. X-ray diffraction analysis revealed that the as-prepared anodized samples contain predominantly hydrated tungstite phases depending on voltage, while films annealed at 400 °C for 4 h are predominantly orthorhombic WO ₃ phase. Photocurrent measurements revealed that the current density of the 2.4 μm nanostructured anodized film was 6 times larger than the nonanodized films. Dye-sensitized solar cells developed using these films produced 0.33 V and 0.65 mA/cm² in open- and short-circuit conditions. © 2009 American Chemical Society.

Abstract: Atomic force microscopy based power spectrum density (PSD) method along with conventional methods such as line, grain height, root mean square (rms) roughness, is used to probe complex Hg-Au interactions i.e. the amalgamation of smooth gold nanostructures (Au-ns) and partial dissolution of irregular edges of interconnecting Au-ns networks due to Hg. We have demonstrated for the first time the use of the PSD method to gain significant insights into the directional anisotropy of resultant Hg-Au-ns and the range of Au-ns responsible. © the Owner Societies 2009.

Abstract: Various methods based on the encapsulation of drug-loaded oleic acid emulsions within 0.5 and 1 μm diameter PMA capsules for the degradable, surfactant free, monodisperse polymer-encapsulated emulsions as anticancer drug carriers are reported. The capsules are found to be redox-responsive in vitro release of encapsulated Dox under reducing conditions, presenting a novel drug-carrier system for lipophilic drugs that would otherwise have restricted accessibility to tumors when injected in the aqueous blood stream. The PMA capsules were dehydrated in ethanol and dispersed in a drug/oleic acid mixture to allow infiltration of the oil phase through the semi-permeable walls of the polymer capsules and filling of the capsules. The experiment focused on PEGylation of the emulsion droplets and the application of these PEGylated oil droplets in tumor targeting, to reload the system in controlled manner.

Abstract: The study of the electrodeposition of polycrystalline gold in aqueous solution is important from the viewpoint that in electrocatalysis applications ill-defined micro- and nanostructured surfaces are often employed. In this work, the morphology of gold was controlled by the electrodeposition potential and the introduction of Pb(CH₃COO)₂3H₂O into the plating solution to give either smooth or nanostructured gold crystallites or large dendritic structures which have been characterized by scanning electron microscopy (SEM). The latter structures were achieved through a novel in situ galvanic replacement of lead with AuCl₄^-_(aq) during the course of gold electrodeposition. The electrochemical behavior of electrodeposited gold in the double layer region was studied in acidic and alkaline media and related to electrocatalytic performance for the oxidation of hydrogen peroxide and methanol. It was found that electrodeposited gold is a significantly better electrocatalyst than a polished gold electrode; however, performance is highly dependent on the chosen deposition parameters. The fabrication of a deposit with highly active surface states, comparable to those achieved at severely disrupted metal surfaces through thermal and electrochemical methods, does not result in the most effective electrocatalyst. This is due to significant premonolayer oxidation that occurs in the double layer region of the electrodeposited gold. In particular, in alkaline solution, where gold usually shows the most electrocatalytic activity, these active surface states may be overoxidized and inhibit the electrocatalytic reaction. However, the activity and morphology of an electrodeposited film can be tailored whereby electrodeposited gold that exhibits nano structure within the crystallites on the surface demonstrated enhanced electrocatalytic activity compared to smaller smooth gold crystallites and larger dendritic structures in potential regions well within the double layer region. © 2009 American Chemical Society.

Abstract: A study was conducted to investigate the galvanic replacement reactions to prepare nanoscale porosity in metal foils. The study also investigated the reaction of Cu²⁺ ions with nickel foil in a Cu-Ni nanoporous surface. The study used scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Auger microscopy, and X-ray photoemission spectroscopy (XPS) analysis to determine the characteristics of the Cu-Ni based nanoporous materials. It was also observed that the highly porous Cu on nickel foil can be used for many application including the catalytic wet air oxidation (CWAO) of ferulic acid. The study also found that a nonoporous Cu-Ni catalyst can oxidize ferulic acid by using mild conditions. The study also provide a method for prepare a nanoscale porosity in bulk surfaces.

Abstract: We report a general and facile approach for the fabrication of a new class of monodispersed, single-component and thick-walled polymer nanocapsules via the single-step assembly of macromolecules in solid core/mesoporous shell (SC/MS) silica particle templates, followed by cross-linking of the macromolecules and removal of the SC/MS templates. The general applicability of this approach is demonstrated by the preparation of nanocapsules using various polymers, including synthetic polyelectrolytes, polypeptides, and polypeptide-drug conjugates. The potential of doxorubicin (Dox)-loaded poly(L-glutamic acid) nanocapsules in tumor therapy applications is demonstrated via in vitro degradation experiments, which show a near-linear release of the Dox in the presence of a lysosomal hydrolase, nanocapsule uptake by human colorectal tumor cells, and delivery of the anticancer drug into the tumor cells, leading to tumor cell death. © 2008 American Chemical Society.

Abstract: One of the important routes for the production of zirconia is by chemical treatment and removal of silica from zircon sand (ZrSi_xO _y). We present here a completely green chemistry approach toward enrichment of zirconia in zircon sand; this is based on the reaction of the fungus Fusarium oxysporum with zircon sand by a process of selective extracellular bioleaching of silica nanoparticles. Since this reaction does not result in zirconia being simultaneously leached out from the sand, there is a consequent enrichment of the zirconia component in zircon sand. We believe that fungal enzymes specifically hydrolyze the silicates present in the sand to form silicic acid, which on condensation by certain other fungal enzymes results in room-temperature synthesis of silica nanoparticles. This fungus-mediated twofold approach might have vast commercial implications in low-cost, ecofriendly, room-temperature syntheses of technologically important oxide nanomaterials from potentially cheap naturally available raw materials like zircon sand. © 2007 American Chemical Society.

Abstract: The syntheses of inorganic materials by biological systems is characterized by processes that occur close to ambient temperatures, pressures, and neutral pH, as is exemplified by biosilicification and biomineralization processes in nature. Conversely, laboratory-based syntheses of oxide materials often require extremes of temperature and pressure. We have shown here the extracellular, room-temperature biosynthesis of 4-5 nm ternary oxide nanoparticles such as barium titanate (BT) using a fungus-mediated approach. The tetragonality as well as a lowered Curie transition temperature in sub-10 nm particles was established, and the ferroelectricity in these particles was shown using Kelvin probe microscopy. © 2006 American Chemical Society.

Abstract: 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. © 2006 American Chemical Society.

Abstract: The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.

Abstract: The synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures, pressures and neutral pH. This is exemplified by biosilicification in marine organisms such as diatoms while laboratory-based synthesis of silica involves extreme temperature and pH conditions. We show here that silica and titania particles may be produced by challenging the fungus Fusarium oxysporum with aqueous anionic complexes SiF₆^2- and TiF₆^2- respectively. Extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of crystalline titania particles while calcination at 300 °C is required for crystallization of silica. © The Royal Society of Chemistry 2005.

Abstract: The fungus Fusarium oxysporum was used in the bioleaching of silica nanoparticles from sand grains. The formation of silica nanoparticles was proceeded in a two-step process, first, leaching out silica from the sand grains in the form of silicic acid by proteins present in the fungul biomass, and then hydrolyzing the silicate complex by other specific proteins in the fungus to silica. The silica was in the form of nanoparticles capped by stabilizing proteins from 2 to 5 nm in size and was released into the solution by the fungus. It was found that the synthesis of oxide nanomaterials using microorganisms starting from potential waste material could lead to eco-friendly and economically viable methods for the large scale synthesis of nanomaterials.

Abstract: Macrophages are one of the principal immune effector cells that play essential roles as secretory, phagocytic, and antigen-presenting cells in the immune system. In this study, we address the issue of cytotoxicity and immunogenic effects of gold nanoparticles on RAW264.7 macrophage cells. The cytotoxicity of gold nanoparticles has been correlated with a detailed study of their endocytotic uptake using various microscopy tools such as atomic force microscopy (AFM), confocal-laser-scanning microscopy (CFLSM), and transmission electron microscopy (TEM). Our findings suggest that Au(0) nanoparticles are not cytotoxic, reduce the production of reactive oxygen and nitrite species, and do not elicit secretion of proinflammatory cytokines TNF-α and IL1-β, making them suitable candidates for nanomedicine. AFM measurements suggest that gold nanoparticles are internalized inside the cell via a mechanism involving pinocytosis, while CFLSM and TEM studies indicate their internalization in lysosomal bodies arranged in perinuclear fashion. Our studies thus underline the noncytotoxic, nonimmunogenic, and biocompatible properties of gold nanoparticles with the potential for application in nanoimmunology, nanomedicine, and nanobiotechnology. © 2005 American Chemical Society.

Abstract: We show here that reaction of the fungus, Fusarium oxysporum, with the aqueous heavy-metal ions Pb²⁺ and Cd²⁺ results in the one-step formation of the corresponding metal carbonates. The metal carbonates are formed by reaction of the heavy-metal ions with CO₂ produced by the fungus during metabolism and thus provide a completely biological method for production of crystals of metal carbonates. The PbCO₃ and CdCO ₃ crystals thus produced have interesting morphologies that are shown to arise because of interaction of the growing crystals with specific proteins secreted by the fungus during reaction. An additional advantage of this approach is that the reaction leads to detoxification of the aqueous solution and could have immense potential for bioremediation of heavy metals. Under conditions of this study, the metal ions are not toxic to the fungus, which readily grows after exposure to the metal ions. © 2005 American Chemical Society.

Abstract: Isothermal titration calorimetry (ITC) is a powerful and highly sensitive technique commonly used to study interactions between biomolecules in dilute aqueous solutions, both from thermodynamic and kinetics points of view. In this report, we show that ITC may be used to follow the binding of ligands such as amino acids to the surface of inorganic materials such as gold nanoparticles. More specifically, we have studied the binding of one basic amino acid, lysine, and an acidic amino acid, aspartic acid, with aqueous gold nanoparticles at physiological pH. Strong binding of aspartic acid with the gold nanoparticles under these conditions is indicated by ITC, while weak binding was observed in the case of lysine. The differences in binding are attributed to protonation of amine groups in lysine at physiological pH (pI ∼ 9.4) while they are not protonated for aspartic acid (pI ∼ 2.77). That this is the likely mechanism is indicated by the ITC measurement of binding of lysine with nanogold at pH 11 (when the amine groups are not protonated). The binding of the amino acids with gold nanoparticles has been validated with other techniques such as gel electrophoresis and X-ray photoemission spectroscopy.

Abstract: Zirconia nanoparticles may be produced by challenging the fungus Fusarium oxysporum with aqueous ZrF₆^2- anions; extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of nanocrystalline zirconia. Extracellular hydrolysis of the metal anions by cationic proteins of molecular weight around 24 to 28 kDa, which are rather similar in nature to silicatein, is shown to be responsible for the synthesis of zirconia nanoparticles, opening up the exciting possibility of large-scale biological synthesis of technologically important oxide materials.

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