Small

Cover image for Vol. 1 Issue 7

July 2005

Volume 1, Issue 7

Pages 669–763

    1. Cover Picture: An Engineered Virus as a Scaffold for Three-Dimensional Self-Assembly on the Nanoscale (Small 7/2005) (page 669)

      Amy Szuchmacher Blum, Carissa M. Soto, Charmaine D. Wilson, Tina L. Brower, Steven K. Pollack, Terence L. Schull, Anju Chatterji, Tianwei Lin, John E. Johnson, Christian Amsinck, Paul Franzon, Ranganathan Shashidhar and Banahalli R. Ratna

      Version of Record online: 9 JUN 2005 | DOI: 10.1002/smll.200590022

      The cover picture shows an STM tip measuring the network conductance of a nanosized network built from molecular conductors using programmed self-assembly; a dramatic illustration of the potential of nanoelectronics. Gold nanoparticles are attached to a modified cowpea mosaic virus scaffold. The particles can then be interconnected using thiol-terminated organic molecules, which act as molecular wires. For more information, please read the Communication "An Engineered Virus as a Scaffold for Three-Dimensional Self-Assembly on the Nanoscale" by A. S. Blum and co-workers on page 702 ff.

    2. The Organometallic Synthesis of Bifunctional Core/Shell Nanoparticles (pages 684–686)

      Mark Green

      Version of Record online: 2 MAY 2005 | DOI: 10.1002/smll.200500085

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      A great double act: Bifunctional core/shell nanomaterials offer important possibilities in a variety of fields, for example, in catalysis and in the (bio)medical sciences. As methods of producing such particles evolve, the utility and quality of the resultant materials is ever increasing. The HRTEM image shows a Co/CdSe core/shell particle, a material that combines magnetic and electronic properties.

    3. Flow Focusing: A Versatile Technology to Produce Size-Controlled and Specific-Morphology Microparticles (pages 688–692)

      Lucía Martín-Banderas, María Flores-Mosquera, Pascual Riesco-Chueca, Alfonso Rodríguez-Gil, Ángel Cebolla, Sebastián Chávez and Alfonso M. Gañán-Calvo

      Version of Record online: 28 APR 2005 | DOI: 10.1002/smll.200500087

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      An innovative technology for microparticle design: Flow focusing, a versatile technique that allows control of the size, surface treatment, and the internal topology of particles is described. Multiplexing and high-rate production can be readily implemented. In a single step, finely tuned microcapsules encasing different products within a targeted morphology can be achieved (see Figure).

    4. Supramolecular Templating of Single and Double Nanohelices of Cadmium Sulfide (pages 694–697)

      Eli D. Sone, Eugene R. Zubarev and Samuel I. Stupp

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200500026

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      Spiraling into control: Single and double nanohelices of cadmium sulfide (CdS) are produced from growth on a self-assembled organic template. Nucleation and growth of CdS on one side of the twisted ribbon-like template leads to single helices of polycrystalline CdS, while nucleation and growth on both sides of the ribbon leads to double helices (see scheme). The early stages of the mineralization process give insight into the templating mechanism that produces these structures.

    5. Assembly of Gold Nanoparticles Using Genetically Engineered Polypeptides (pages 698–702)

      Melvin T. Zin, Hong Ma, Mehmet Sarikaya and Alex K.-Y. Jen

      Version of Record online: 13 MAY 2005 | DOI: 10.1002/smll.200400164

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      Laterally structured hybrid assemblies composed of genetically engineered polypeptides and fused-ring organic molecules were used to guide the assembly of gold nanoparticles in a site-selective fashion (see image). Gold-binding protein was covalently bonded onto a self-assembled monolayer of preformed, π-conjugated thiols on a Au(111) substrate by microcontact printing to produce a 2D template with submicrometer patterns. The assembly of gold nanoparticles occurred through surface recognition.

    6. An Engineered Virus as a Scaffold for Three-Dimensional Self-Assembly on the Nanoscale (pages 702–706)

      Amy Szuchmacher Blum, Carissa M. Soto, Charmaine D. Wilson, Tina L. Brower, Steven K. Pollack, Terence L. Schull, Anju Chatterji, Tianwei Lin, John E. Johnson, Christian Amsinck, Paul Franzon, Ranganathan Shashidhar and Banahalli R. Ratna

      Version of Record online: 8 JUN 2005 | DOI: 10.1002/smll.200500021

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      Exquisite control over positioning nanoscale components on a protein scaffold allows bottom-up self-assembly of nanodevices. Using cowpea mosaic virus, modified to express cysteine residues on the capsid exterior, gold nanoparticles were attached to the viral scaffold to produce specific interparticle distances (see picture). The nanoparticles were then interconnected using thiol-terminated conjugated organic molecules that act as “molecular wires”, resulting in a 3D spherical conductive network, which is only 30 nm in diameter.

    7. On the Generation of Free Radical Species from Quantum Dots (pages 706–709)

      Binil Itty Ipe, Manfred Lehnig and Christof M. Niemeyer

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200500105

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      Radical discoveries? Semiconductor quantum dots (QDs) produce free radicals upon UV irradiation in aqueous solution. While CdS QDs generate superoxide and hydroxyl radicals, only the latter are produced from CdSe QDs. In contrast, CdSe/ZnS core/shell QDs, often applied in biolabeling applications, do not generate radicals.

    8. Using Gene Regulation to Program DNA-Based Molecular Devices (pages 709–712)

      Wendy U. Dittmer, Susanne Kempter, Joachim O. Rädler and Friedrich C. Simmel

      Version of Record online: 4 MAY 2005 | DOI: 10.1002/smll.200500074

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      DNA-based nanodevices can perform increasingly more complex and useful functions. To permit DNA nanomachines to act independently and respond to environmental stimuli, the instructions for the control of the machines can be encoded into a gene regulated by genetic switches from the SOS regulon and lac operon (see image). Depending on the presence of regulatory proteins or chemical inducers, mRNA signals are transcribed that bring about machine action.

    9. Size-Dependent Photoconductance in SnO2 Nanowires (pages 713–717)

      Sanjay Mathur, Sven Barth, Hao Shen, Jae-Chul Pyun and Ulf Werner

      Version of Record online: 13 MAY 2005 | DOI: 10.1002/smll.200400168

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      Tin oxide (SnO2) nanowires of different diameters can be conveniently grown by combining the chemical influence of a single-molecular precursor [Sn(OtBu)4] with vapor–liquid–solid growth. Upon illumination with UV light at a wavelength of 370 nm, the nanowires exhibit interesting photoconductance, which can be modulated by tuning the wire diameter, as demonstrated for samples possessing radial dimensions in the range 50–1000 nm (see image).

    10. Crystallography and Surface Faceting of Germanium Nanowires (pages 717–721)

      Tobias Hanrath and Brian A. Korgel

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200500033

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      Key crystallographic aspects of Ge nanowires grown in a supercritical fluid were investigated by high-resolution transmission electron microscopy. The favored <110> growth direction was attributed to the crystallographic faceting of low-energy {111} and {100} planes on the initial nucleus crystal and the exposed nanowire sidewall surfaces. Electron diffraction patterns of individual nanowires exhibited forbidden 1/3 {422} reflections due to incomplete {111} surface facets and the finite size of the nanowires.

    11. Self-Organized High-Aspect-Ratio Nanoporous Zirconium Oxides Prepared by Electrochemical Anodization (pages 722–725)

      Hiroaki Tsuchiya, Jan M. Macak, Irina Sieber and Patrik Schmuki

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200400163

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      Getting organized: Highly ordered porous ZrO2 layers and nanotubes with very high aspect ratios (see SEM image) can be prepared by direct anodization of Zr in fluoride-containing electrolyte. The morphology of the layers is strongly affected by the electrochemical parameters used. Under optimized conditions, the ZrO2 layers have a cubic structure and are candidates for use in applications such as catalysis, due to their high surface area and defined geometry.

    12. A Tunnel Current in Self-Assembled Monolayers of 3-Mercaptopropyltrimethoxysilane (pages 725–729)

      Dinesh K. Aswal, Stephane Lenfant, David Guerin, Jatinder V. Yakhmi and Dominique Vuillaume

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200500052

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      The current density–voltage (J–V) characteristics of self-assembled monolayers of 3-mercaptopropyltrimethoxysilane (MPTMS) chemisorbed on the native oxide surface of p+-doped Si demonstrate the excellent tunnel dielectric behavior of organic monolayers down to three carbon atoms (see image).

    13. Water-Soluble Sacrificial Layers for Surface Micromachining (pages 730–736)

      Vincent Linder, Byron D. Gates, Declan Ryan, Babak A. Parviz and George M. Whitesides

      Version of Record online: 3 MAY 2005 | DOI: 10.1002/smll.200400159

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      Wetter is better! Water-soluble sacrificial layers are useful for the rapid fabrication of all-polymer microsystems, and extend the capabilities of conventional micromachining. A reversible ion-exchange reaction with calcium ions renders the initially water-soluble polymer insoluble in water. To illustrate the capabilities of this method, the SEM image shows a microfabricated bridge made of epoxy, stretching over a sheet of plastic.

    14. Organic-Dye-Coupled Magnetic Nanoparticles Encaged Inside Thermoresponsive PNIPAM Microcapsules (pages 737–743)

      Jia Guo, Wuli Yang, Yonghui Deng, Changchun Wang and Shoukuan Fu

      Version of Record online: 13 MAY 2005 | DOI: 10.1002/smll.200400145

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      Thermoresponsive, magnetic, and fluorescent: Organic–inorganic composite microspheres composed of a crosslinked poly(N-isopropylacrylamide) (PNIPAM) shell and a silica core containing Fe3O4 nanoparticles were prepared. The silica layers sandwiched between the Fe3O4 and PNIPAM were then quantitatively removed. Finally, fluorescein isothiocyanate (FITC) was attached to the insides of the magnetic cores to form PNIPAM microcapsules with mobile FITC-labeled magnetic cores (see AFM image).

    15. Simple Synthesis of Hierarchically Ordered Mesocellular Mesoporous Silica Materials Hosting Crosslinked Enzyme Aggregates (pages 744–753)

      Jinwoo Lee, Jungbae Kim, Jaeyun Kim, Hongfei Jia, Moon Il Kim, Ja Hun Kwak, Sunmi Jin, Alice Dohnalkova, Hyun Gyu Park, Ho Nam Chang, Ping Wang, Jay W. Grate and Taeghwan Hyeon

      Version of Record online: 11 MAY 2005 | DOI: 10.1002/smll.200500035

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      Hierarchically ordered mesocellular mesoporous silica materials (HMMS) were synthesized using a single structure-directing agent under neutral conditions. The mesocellular pores are synthesized without adding any pore expander, and the walls of the cellular pores are composed of SBA-15-type one-dimensional mesopores. Crosslinked enzyme aggregates (CLEAs) formed in the pores of HMMS show impressive stability coupled with extremely high enzyme loading.

    16. Ionogel-Templated Synthesis and Organization of Anisotropic Gold Nanoparticles (pages 754–760)

      Millicent A. Firestone, Mark L. Dietz, Sönke Seifert, Susana Trasobares, Dean J. Miller and Nestor J. Zaluzec

      Version of Record online: 13 MAY 2005 | DOI: 10.1002/smll.200500030

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      Golden rods: The nanostructured gel formed by self-assembly of the ionic liquid 1-decyl-3-methylimidazolium chloride in water comprises a unique soft template for the preparation and organization of anisotropic gold nanoparticles of a variety of sizes and shapes (see picture), such as trigonal prismatic nanorods. The polarized optical micrograph shows a thin film of ionic liquid containing HAuCl4 after irradiation at 254 nm for 70 min.

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      Preview: Small 7/2005 (page 763)

      Version of Record online: 8 JUN 2005 | DOI: 10.1002/smll.200590021

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