A revolution in novel nanoparticles and colloidal building blocks has been enabled by recent breakthroughs in particle synthesis These new particles are poised to become the ‘atoms’ and ‘molecules’ of tomorrow’s materials if they can be successfully assembled into useful structures Here, we discuss the recent progress made in the synthesis of nanocrystals and colloidal particles and draw analogies between these new particulate building blocks and better-studied molecules and supramolecular objects We argue for a conceptual framework for these new building blocks based on anisotropy attributes and discuss the prognosis for future progress in exploiting anisotropy for materials design and assembly

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Anisotropy of building blocks and their assembly into complex structures

Nanotechnology involves the production, manipulation and use of materials ranging in size from less than a micron to that of individual atoms. Although nanomaterials may be synthesized using chemical approaches, it is now possible to include the use of biological materials. In this review, we critically assess the role of microorganisms and plants in the synthesis of nanoparticles.

Biosynthesis of nanoparticles: technological concepts and future applications

Biological synthesis of metal nanoparticles by microbes.

https://www.rsc.org/suppdata/gc/b6/b615357g/b615357g.pdf

Green synthesis of silver nanoparticles using Capsicum annuum L. extract

Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

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25th Anniversary Article: Semiconductor Nanowires – Synthesis, Characterization, and Applications

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.

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Fungus-mediated biosynthesis of silica and titania particles

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.

Biological synthesis of strontium carbonate crystals using the fungus Fusarium oxysporum

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.

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

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 CdCO3 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.

Heavy-metal remediation by a fungus as a means of production of lead and cadmium carbonate crystals.

A plant pathogenic fungus, Fusarium oxysporum, can be used as a biological model system for the extracellular bioleaching of hollow spherical silica nanoparticles (see Figure) from sand. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential waste materials could lead to eco-friendly and economically viable methods for the large-scale synthesis of nanomaterials.

Ambarish Sanyal

Papers

Fungus-mediated biosynthesis of silica and titania particles

Biological synthesis of strontium carbonate crystals using the fungus Fusarium oxysporum

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

Heavy-metal remediation by a fungus as a means of production of lead and cadmium carbonate crystals.

Bioleaching of Sand by the Fungus Fusarium oxysporum as a Means of Producing Extracellular Silica Nanoparticles