In the last 30 days

• Open/close A simple low temperature synthesis route for ZnO–MgO core–shell nanowires

  N O V Plank et al 2008 Nanotechnology 19 465603 Tag this article

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  We report a hydrothermal synthesis method for MgO shell coatings directly onto the surface of ZnO nanowire arrays. The entire process can be carried out below 100 °C. The MgO shells are produced by the addition of 10 mM magnesium nitrate with 0.2 M sodium hydroxide in water, resulting in a shell thickness of up to 8 nm, verified by high resolution transmission electron microscopy. The viability of the MgO layer as a functional element of optoelectronic devices was tested on solid-state organic hole-transporter based dye-sensitized solar cells. Incorporation of the MgO shell into the solar cell resulted in substantive efficiency improvements of over 400% in comparison to the pristine ZnO nanowire based photovoltaics, indicating that electrons can efficiently tunnel through the 'insulating' MgO shell.

• Open/close Intracellular protein delivery by hollow mesoporous silica capsules with a large surface hole

  Ji-Sun Lim et al 2012 Nanotechnology 23 085101 Tag this article

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  We prepared cell membrane-permeable hollow mesoporous silica capsules (HMSCs) by a simple new method. CTAB micellar assembly in cholesterol emulsion gave rise to a novel capsular morphology of the HMSC particles. The HMSCs consisted of mesostructured silica walls with a large surface hole (25–50 nm) and the average particle dimension was 100–300 nm. They exhibited high surface areas of up to 719.3 m ² g ⁻¹ and a mesoporous range of pores of 2.4–2.7 nm. The surface-functionalized HMSCs could also be prepared by a similar co-condensation method using tetraethoxysilane with various organoalkoxysilane precursors in the presence of cholesterol. These organically modified HMSCs could be further modified on demand. For example, a carboxy-functionalized HMSC could be surface-functionalized by a green fluorescent 5-aminofluorescein (AFL) through an amidation reaction to afford a fluorescent AFL–HMSC. The hollow capsular morphology of the HMSCs with a large surface hole enabled us to develop very efficient intracellular delivery systems for membrane-impermeable ions, molecules, and various functional proteins. Non-covalent sequestration and delivery of proteins as well as covalent linkage of fluorescent molecules on the silica surface are effective for this system. The highly negatively charged green fluorescent probe mag-fluo-4 could be intracellularly delivered into HeLa cells by HMSC without any difficulty. The HMSCs could also effectively transport large functional proteins such as antibodies into HeLa cells. The efficiency of protein delivery by HMSC seems to be 3–22-fold higher than that of mesoporous silica nanospheres (MSNs) based on confocal laser scanning microscopy (CLSM) analysis.

• Open/close A room temperature ethanol sensor made from p-type Sb-doped SnO₂ nanowires

  Jyh Ming Wu 2010 Nanotechnology 21 235501 Tag this article

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  A p-type ethanol sensor with a response time of ~ 8.3 s at room temperature was produced by SnO ₂:Sb nanowires. The electrical properties of p-type SnO ₂ nanowires are stable with a hole concentration of 1.544 × 10 ¹⁷ cm ^{− 3} and a field-effect mobility of 22 cm ² V ^{− 2} S ^{− 1}. X-ray photoelectron spectroscopy (XPS) and Hall measurement revealed that as-synthesized nanowires exhibit p-type behavior. A comprehensive investigation of the p-type sensing mechanism is reported.

• Open/close Emission properties of hydrothermal Yb^{3 +} , Er^{3 +} and Yb^{3 +} , Tm^{3 +} -codoped Lu₂O₃ nanorods: upconversion, cathodoluminescence and assessment of waveguide behavior

  Elixir William Barrera et al 2011 Nanotechnology 22 075205 Tag this article

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  Yb ^{3 +} and Ln ^{3 +} (Ln ^{3 +} = Er ^{3 +} or Tm ^{3 +} ) codoped Lu ₂O ₃ nanorods with cubic symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb ⁺ concentration in the prepared nanorods. UC spectra revealed the strong development of (red) and (blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb ^{3 +} concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of  ⁴F _9/2 and ¹G ₄ emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the (red) and ²H _11/2, (green) emissions with the increase in the Yb ^{3 +} content, while for Yb ^{3 +} , Tm ^{3 +} -codoped Lu ₂O ₃ nanorods the dominant CL emission is (deep-blue). Uniform light emission along Yb ^{3 +} , Er ^{3 +} -codoped Lu ₂O ₃ rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light.

• Open/close One-step solvothermal synthesis of Fe₃O₄@C core–shell nanoparticles with tunable sizes

  J Zheng et al 2012 Nanotechnology 23 165601 Tag this article

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  We report the synthesis of Fe ₃O ₄@C core–shell nanoparticles (FCNPs) by using a facile one-step solvothermal method. The FCNPs consisted of Fe ₃O ₄ particles as the cores and amorphous uniform carbon shells. The content of Fe ₃O ₄ is up to 81.6 wt%. These core–shell nanoparticles are aggregated by primary nanocrystals with a size of 10–12 nm. The FCNPs possess a hollow interior, high magnetization, excellent absorption properties and abundant surface hydroxyl groups. A possible growth mechanism of the FCNPs is proposed. The role of glucose in regulating the grain size and morphology of the particles is discussed. The absorption properties of the FCNPs towards Cr(VI) in aqueous solution is investigated. We demonstrate that the FCNPs can effectively remove more than 90 wt% of Cr(VI) from aqueous solution.

• Open/close The application of graphene as electrodes in electrical and optical devices

  Gunho Jo et al 2012 Nanotechnology 23 112001 Tag this article

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  Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials such as indium tin oxide in electrical and optical devices. It combines several advantageous characteristics including low sheet resistance, high optical transparency and excellent mechanical properties. Recent research has coincided with increased interest in the application of graphene as an electrode material in transistors, light-emitting diodes, solar cells and flexible devices. However, for more practical applications, the performance of devices should be further improved by the engineering of graphene films, such as through their synthesis, transfer and doping. This article reviews several applications of graphene films as electrodes in electrical and optical devices and discusses the essential requirements for applications of graphene films as electrodes.

• Open/close Optical and electrical properties of indium tin oxide nanofibers prepared by electrospinning

  Muhammad Miftahul Munir et al 2008 Nanotechnology 19 145603 Tag this article

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  Indium tin oxide (ITO) nanofibers were successfully prepared via an electrospinning method, followed by annealing at 400 °C. Mixed solutions of ITO nanoparticle sol and polyethylene oxide (PEO) were used as precursors of the nanofibers. The PEO decomposed during annealing to yield ITO fibers. The fibers were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermo-gravimetric/differential thermal analysis (TG/DTA), UV–vis spectrophotometry and four-probe resistivity measurements. The diameter of the prepared fibers was controlled by adjusting the flow rate and the applied electric current. In ₂O ₃ crystallized in the ITO nanofibers with a crystallite size of 27 nm. The optical transmittance in the visible region approached 90% in films deposited for 5 min, confirming that the nanofiber film is still transparent in the optical region. The sheet resistance of the nanofiber film was linearly dependent on the inverse of the deposition time and on the PEO/ITO ratio.

• Open/close A three-dimensional, biaxially textured oxide nanofence composed of MgO single crystal nanobelt segments

  Sung Hun Wee et al 2009 Nanotechnology 20 215608 Tag this article

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  A unique, three-dimensional (3D), biaxially textured, MgO, nanofence comprised of single crystal MgO nanobelt segments or links was synthesized via epitaxial growth on (100) SrTiO ₃ substrates. Individual single crystal MgO nanobelt segments comprising the nanofence have a square cross-section with dimensions in the range of 10–20 nm and with lengths in the range from 100 nm up to 1 µm. X-ray diffraction shows that the 3D MgO nanofence has an epitaxial relation with (100) SrTiO ₃ substrates with a cube-on-cube, {100} 100 orientation and with values of the full width at half-maximum of the (200) ω-scan and the (110) -scan at 4.5° and 5.5°, respectively. Such a biaxially textured oxide nanofence with single crystal segments can be used as a 3D nanotemplated substrate for epitaxial growth of wide-ranging, 3D, electronic, magnetic and electromagnetic nanodevices.

• Open/close Core/shell fluorescent magnetic silica-coated composite nanoparticles for bioconjugation

  Rong He et al 2007 Nanotechnology 18 315601 Tag this article

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  A new class of highly fluorescent, photostable, and magnetic core/shell nanoparticles has been synthesized from a reverse microemulsion method. The obtained bifunctional nanocomposites were characterized by transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectrometry, photoluminescence (PL) spectrometry, and fluorescence microscopy in a magnetic field. To further improve their biocompatibility, the silica-coated nanoparticles were functionalized with amino groups. The fluorescent magnetic composite nanoparticles (FMCNPs) had a typical diameter of 50 ± 5 nm and a saturation magnetization of 3.21 emu g ⁻¹ at room temperature, and exhibited strong excitonic photoluminescence. Through activation with glutaraldehyde, the FMCNPs were successfully conjugated with goat anti-mouse immunoglobin G (GM IgG), and the bioactivity and binding specificity of the as-prepared FMCNPs-GM IgG were confirmed via immunofluorescence assays, commonly used in bioanalysis. So they are potentially useful for many applications in biolabelling, imaging, drug targeting, bioseparation and bioassays.

• Open/close Enzyme-assisted formation of nanosphere: a potential carrier for hydrophobic compounds

  Huaimin Wang et al 2010 Nanotechnology 21 155602 Tag this article

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  In this study, we report the use of a phosphatase to catalyze the formation of nanospheres from a hydrophobic compound (Ada-GFFY-OMe, 2) via a unique mechanism. The nanospheres were stable in aqueous solutions for two weeks. Their size could be controlled by both concentrations of the precursor (Ada-GFFY(p)-OMe, 1) and the enzyme and the nanospheres were characterized by SEM and dynamic light scattering (DLS). We then demonstrated that nanospheres could help the cell-impermeable propidium iodine (PI) to penetrate the cells, which implied that the nanospheres have the potential to be developed into useful carriers for hydrophobic drugs. This study offers the first example of using an enzyme to control the formation of nanospheres from a hydrophobic compound. There is thus the potential that nanospheres can be developed into a carrier for hydrophobic drugs.