Ambarish Sanyal

Fungus-mediated biosynthesis of silica and titania particles

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 SiF62− and TiF62− 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.

Spontaneous room temperature elongation of CdS and Ag2S nanorods via oriented attachment.

Spontaneous elongation from nanorod to nanowire in the presence of an amine is reported for nanocrystals of cadmium sulfide and silver sulfide (cation exchanged from CdS). Elongation occurs instantaneously where the final aspect ratio is a controllable multiple of the original nanorod length. Transmission electron microscopy (TEM) analysis reveals the influential factors on the attachment process are the concentration of amine, duration and temperature of the reaction. The elongated nanorods are further characterized by X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS). A mechanism of oriented attachment is evidenced by the doubling in length of asymmetrically gold tipped CdS nanorods with the corresponding absence of elongation in symmetrically tipped nanorods.

Gold nanosheets via reduction of aqueous chloroaurate ions by anthracene anions bound to a liquid-liquid interface

Anthracene anions bound to a liquid-liquid interface and charged by photochemically reduced Keggin ions when exposed to aqueous chloroaurate ions result in the formation of high concentration of thin, gold nanosheets at the interface.

Water Dispersible Semiconductor Nanorod Assemblies Via a Facile Phase Transfer and Their Application as Fluorescent Biomarkers

We demonstrate the formation of water dispersed nanorod assemblies by phase transfer of semiconductor (CdS, CdSe, CdTe) nanorods from the organic to the aqueous using pluronic triblock copolymers. On phase transfer, the randomly dispersed nanorods in the organic medium close pack in the form of discs encapsulated in the hydrophobic core of water dispersible micelles. The assemblies showed excellent cellular uptake exhibiting membrane and cell specific fluorescence at low light intensity under confocal microscopy.

Fabrication of Noble metal-semiconductor hybrid nanostructures using phase transfer

An easy and effective solution based procedure for the synthesis of noble metal (both Au and Ag) tipped semiconductor nanomaterials is demonstrated where the metal precursors are taken in water and the semiconductors in organic medium, exploiting the phase transfer and reducing capability of suitably chosen ligands. The phase tranfer route is a generalised approach to form either Ag or Au tips on cadmium chalcogenide nanoparticles and nanorods. While multiple dots of noble metals are formed on the semiconductor nanomaterials initially, these coalesce into larger islands with time. The hybrids are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS). A detailed FTIR analysis was also carried out to delineate the role of the ligands in the synthesis.Graphical abstract

Silver Tip Formation on Colloidal CdSe Nanorods by a Facile Phase Transfer Protocol

A facile phase transfer procedure is described for the formation of uniform silver metal tips on II–VI semiconductor nanorods. Judicious choice of a functional ligand dimethyl phenol (DMP) which binds to the semiconductor rod in the organic phase enables the transfer of metal ions from the aqueous phase and their reduction onto the nanorod. The nanorod hybrids can be assembled into perpendicularly aligned arrays by simple solvent evaporation.

Organic–inorganic hybrid: a novel template for synthesis of nanostructured Ag

We herein demonstrate that the amino acid arginine (Arg) can interact with phosphotungstate (Keggin) anions generating an excellent template for the synthesis of nanostructured silver wherein the Arg–PTA hybrid host plays the role of a UV-switchable reducing agent. The binding strength of the complex between arginine and phosphotungstate (PW12O40)3− i.e. the Keggin ions in aqueous medium has been assessed by the isothermal titration calorimetric technique. It is shown that the Arg–PTA complex may be used as a new class of organic–inorganic scaffolds in the synthesis of nanostructured silver. The crystalline Arg–PTA host can be photochemically reduced, resulting in electron transfer to the entrapped silver ions to form nanoparticle assemblies on the underlying colloidal template.

Keggin-lysine hybrid nanostructures in the shape modulation of gold

We show here that L-lysine effectively complexes with phosphomolybdic acid (PMA) and the solution mixture when added to a 10 �3 M aqueous solution of HAuCl4 after UV-irradiation for 3 h leads to the slow reduction and consequent formation of gold nanotriangles with a high degree of anisotropy. The same reaction carried out in a 12.5 kDa cutoff dialysis bag where the irradiated PMAlysine solution was kept inside and stirred in a beaker containing aqueous HAuCl4, did not lead to the formation of gold nanotriangles. This implies that L-lysine plays the role of a shape-modulating agent and hence this study proves an improvement in the understanding of the role of such organic–inorganic hybrid structures in the synthesis and growth of anisotropic nanoparticles. S Online supplementary data available from stacks.iop.org/MRX/1/015007/ mmedia