In the last 30 days

• Open/close Biomimetic synthesis of oriented hydroxyapatite mediated by nonionic surfactants

  Feng Ye et al  2008 Nanotechnology 19 245605 Tag this article

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  Highly oriented organization of hydroxyapatite (HAP) nanorods was achieved through a simple reflux method using mixtures of triblock copolymer pluronic P123 and tween-60 as the mediated agents. Raft-like organized complexes were prepared when the nanorods were only directed by the mixed surfactants. Bundles of nanorod-like HAP crystals were obtained when urea was used as the cosurfactant. These HAP nanorods with a large amount of uniform 4 nm worm-like mesopores were arranged in parallel to each other along the c axis of HAP. The raft-like complexes might be mediated by the reverse lamellar micelles. And the added urea transformed the reverse lamellar micelles into hexagonal ones due to its association with the surfactant molecules by hydrogen bonds, resulting in the formation of bundles of nanorod-like HAP crystals. The regulation of the oriented HAP complexes in morphology extends the understanding of biomineralization and permits controllable design of biomimetic materials. In addition, the c-axis oriented raft-like HAP complex has great potential in selective bio-absorption and separation.

• Open/close Highly biocompatible and water-dispersible, amine functionalized magnetite nanoparticles, prepared by a low temperature, air-assisted polyol process: a new platform for bio-separation and diagnostics

  Manasmita Das et al  2010 Nanotechnology 21 125103 Tag this article

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  A low temperature polyol process, based on glycolaldehyde mediated partial reduction of FeCl ₃·6H ₂O at 120 °C in the presence of sodium acetate as an alkali source and 2, 2 ^'-(ethylenedioxy)-bis-(ethylamine) as an electrostatic stabilizer has been used for the gram-scale preparation of biocompatible, water-dispersible, amine functionalized magnetite nanoparticles (MNPs) with an average diameter of 6 ± 0.75 nm. With a reasonably high magnetization (37.8 e.m.u.) and amine groups on the outer surface of the nanoparticles, we demonstrated the magnetic separation and concentration implications of these ultrasmall particles in immunoassay. MRI studies indicated that these nanoparticles had the desired relaxivity for T ₂ contrast enhancement in vivo. In vitro biocompatibility, cell uptake and MR imaging studies established that these nanoparticles were safe in clinical dosages and by virtue of their ultrasmall sizes and positively charged surfaces could be easily internalized by cancer cells. All these positive attributes make these functional nanoparticles a promising platform for further in vitro and in vivo evaluations.

• Open/close Crossover behavior in the hydrogen sensing mechanism for palladium ultrathin films

  M Ramanathan et al  2010 Nanotechnology 21 125501 Tag this article

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  Palladium has been extensively studied as a material for hydrogen sensors because of the simplicity of its reversible resistance change when exposed to hydrogen gas. Various palladium films and nanostructures have been used, and different responses have been observed with these diverse morphologies. In some cases, such as with nanowires, the resistance will decrease, whereas in others, such as with thick films, the resistance will increase. Each of these mechanisms has been explored for several palladium structures, but the crossover between them has not been systematically investigated. Here we report on a study aimed at deciphering the nanostructure–property relationships of ultrathin palladium films used as hydrogen gas sensors. The crossover in these films is observed at a thickness of ~ 5 nm. Ramifications for future sensor developments are discussed.

• Open/close The bactericidal effect of silver nanoparticles

  Jose Ruben Morones et al  2005 Nanotechnology 16 2346 Tag this article

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  Nanotechnology is expected to open new avenues to fight and prevent disease using atomic scale tailoring of materials. Among the most promising nanomaterials with antibacterial properties are metallic nanoparticles, which exhibit increased chemical activity due to their large surface to volume ratios and crystallographic surface structure. The study of bactericidal nanomaterials is particularly timely considering the recent increase of new resistant strains of bacteria to the most potent antibiotics. This has promoted research in the well known activity of silver ions and silver-based compounds, including silver nanoparticles. The present work studies the effect of silver nanoparticles in the range of 1–100 nm on Gram-negative bacteria using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Our results indicate that the bactericidal properties of the nanoparticles are size dependent, since the only nanoparticles that present a direct interaction with the bacteria preferentially have a diameter of ~1–10 nm.

• Open/close The preparation of a plasmonically resonant VO₂ thermochromic pigment

  Huaping Bai et al  2009 Nanotechnology 20 085607 Tag this article

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  Vanadium dioxide (VO ₂) undergoes a reversible metal–insulator transition, normally at ~68 °C. While the properties of continuous semi-transparent coatings of VO ₂ are well known, there is far less information available concerning the potential use of discrete VO ₂ nanoparticles as a thermochromic pigment in opaque coatings. Individual VO ₂ nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO ₂ nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO ₂ powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.

• Open/close A novel method for metal oxide nanowire synthesis

  Simas Rackauskas et al  2009 Nanotechnology 20 165603 Tag this article

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  Nanowires (NWs) of metal oxides (Fe ₂O ₃, CuO, V ₂O ₅ and ZnO) were grown by an efficient non-catalytic economically favorable method based on resistive heating of pure metal wires or foils at ambient conditions. The growth rate of iron oxide NWs exceeds 100 nm s ⁻¹. Produced NWs were typically 1–5 µm long with diameters from 10 to 50 nm. The produced metal oxide NWs were characterized by means of SEM, TEM, EDX, XPS and Raman techniques. The field emission measurements from the as-produced CuO NWs were found to have a threshold field as low as 4 V µm ⁻¹ at 0.01 mA cm ⁻². The formation mechanism of the NWs is discussed.

• Open/close Gold hybrid nanoparticles for targeted phototherapy and cancer imaging

  Dickson K Kirui et al  2010 Nanotechnology 21 105105 Tag this article

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  Gold and iron oxide hybrid nanoparticles (HNPs) synthesized by the thermal decomposition technique are bio-functionalized with a single chain antibody, scFv, that binds to the A33 antigen present on colorectal cancer cells. The HNP–scFv conjugates are stable in aqueous solution with a magnetization value of 44  emu g ^{− 1} and exhibit strong optical absorbance at 800 nm. Here we test this material in targeting, imaging and selective thermal killing of colorectal cancer cells. Cellular uptake studies showed that A33-expressing cells take up the A33scFv-conjugated HNPs at a rate five times higher than cells that do not express the A33 antigen. Laser irradiation studies showed that approximately 53% of the A33-expressing cells exposed to targeted HNPs are killed after a six-minute laser treatment at 5.1  W cm ^{− 2} using a 808 nm continuous wave laser diode while < 5% of A33-nonexpressing cells are killed. At a higher intensity, 31.5  W cm ^{− 2}, the thermal destruction increases to 99 and 40% for A33-expressing cells and A33 nonexpressing cells, respectively, after 6 min exposure. Flow cytometric analyses of the laser-irradiated A33 antigen-expressing cells show apoptosis-related cell death to be the primary mode of cell death at 5.1  W cm ^{− 2}, with increasing necrosis-related cell death at higher laser power. These results suggest that this new class of bio-conjugated hybrid nanoparticles can potentially serve as an effective antigen-targeted photothermal therapeutic agent for cancer treatment as well as a probe for magnetic resonance-based imaging.

• Open/close Triple-twin domains in Mg doped GaN wurtzite nanowires: structural and electronic properties of this zinc-blende-like stacking

  Jordi Arbiol et al  2009 Nanotechnology 20 145704 Tag this article

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  We report on the effect of Mg doping on the properties of GaN nanowires grown by plasma assisted molecular beam epitaxy. The most significant feature is the presence of triple-twin domains, the density of which increases with increasing Mg concentration. The resulting high concentration of misplaced atoms gives rise to local changes in the crystal structure equivalent to the insertion of three non-relaxed zinc-blende (ZB) atomic cells, which result in quantum wells along the wurtzite (WZ) nanowire growth axis. High resolution electron energy loss spectra were obtained exactly on the twinned (zinc-blende) and wurtzite planes. These atomically resolved measurements, which allow us to identify modifications in the local density of states, revealed changes in the band to band electronic transition energy from 3.4 eV for wurtzite to 3.2 eV in the twinned lattice regions. These results are in good agreement with specific ab initio atomistic simulations and demonstrate that the redshift observed in previous photoluminescence analyses is directly related to the presence of these zinc-blende domains, opening up new possibilities for band-structure engineering.

• Open/close Nonvolatile memory devices based on few-layer graphene films

  Yong-Joo Doh and Gyu-Chul Yi  2010 Nanotechnology 21 105204 Tag this article

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  We report on the electrical characteristics of few-layer graphene (FLG) field-effect devices with their various thicknesses. In combination with a ferroelectric polymer layer of poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)], FLG/ferroelectric devices exhibited nonvolatile resistance changes due to a polarization switching of the P(VDF/TrFE) layer. The bistability and retention properties were highly sensitive to the FLG thickness, which is attributed to a charge screening effect in FLG films.

• Open/close L-cysteine-capped CdTe QD-based sensor for simple and selective detection of trinitrotoluene

  Yufang Chen et al  2010 Nanotechnology 21 125502 Tag this article

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  Trinitrotoluene, usually known as TNT, is a kind of chemical explosive with hazardous and toxic effects on the environment and human health. National and societal security concerns have dictated an increasing need for the analytical detection of TNT with rapidity, high sensitivity and low cost. This work demonstrates a novel method using L-cysteine-capped CdTe quantum dots (QDs) to assay TNT, based on the formation of a Meisenheimer complex between TNT and cysteine. The fluorescence (FL) of quantum dots quench because electrons of the QDs transfer to the TNT molecules via the formation of a Meisenheimer complex. TNT can be detected with a low detection limit of 1.1 nM. Studies on the selectivity of this method show that only TNT can generate an intense signal response. The synthesized QDs are excellent nanomaterials for TNT detection. In addition, TNT in soil samples is also analyzed by the proposed method.