Showing papers by "Xiaogang Liu published in 2008"

Upconversion multicolor fine-tuning: visible to near-infrared emission from lanthanide-doped NaYF4 nanoparticles.

Abstract: A general approach to fine-tuning the upconversion emission colors, based upon a single host source of NaYF4 nanoparticles doped with Yb3+, Tm3+, and Er3+, is presented. The emission intensity balance can be precisely controlled using different host-activator systems and dopant concentrations. The approach allows access to a wide range of luminescence emission from visible to near-infrared by single-wavelength excitation.

Superwetting nanowire membranes for selective absorption

Abstract: The construction of nanoporous membranes is of great technological importance for various applications, including catalyst supports, filters for biomolecule purification, environmental remediation and seawater desalination. A major challenge is the scalable fabrication of membranes with the desirable combination of good thermal stability, high selectivity and excellent recyclability. Here we present a self-assembly method for constructing thermally stable, free-standing nanowire membranes that exhibit controlled wetting behaviour ranging from superhydrophilic to superhydrophobic. These membranes can selectively absorb oils up to 20 times the material's weight in preference to water, through a combination of superhydrophobicity and capillary action. Moreover, the nanowires that form the membrane structure can be re-suspended in solutions and subsequently re-form the original paper-like morphology over many cycles. Our results suggest an innovative material that should find practical applications in the removal of organics, particularly in the field of oil spill cleanup.

One-step, room temperature, colorimetric detection of mercury (Hg2+) using DNA/nanoparticle conjugates.

Abstract: Introduction of Hg2+ into an aqueous solution containing oligonucleotide-tethered gold nanoparticle probes and a linker oligonucleotide with a number of thymine−thymine (T−T) mismatches results in the formation of particle aggregates at room temperature with a concomitant colorimetric response. The high selectivity of this detection system is attributed to Hg2+-mediated formation of T−Hg2+−T base pairs as evidenced by an increase in a sharp melting temperature.

Multicolor Tuning of (Ln, P)-Doped YVO4 Nanoparticles by Single-Wavelength Excitation†

Abstract: Fluorescent probes enable researchers to encode chemical information and to detect particular components of complex biomolecular assemblies, such as live cells, with substantial sensitivity and selectivity. Multicolor labeling experiments entail the deliberate introduction of two or more fluorescent probes to simultaneously monitor different biochemical functions. This approach has applications in areas as diverse as drug discovery, catalyst screening, DNA sequencing, fluorescent microscopy, and clinical diagnostics. Ideal probes for multicolor labeling would exhibit considerable photochemical stability, strong absorption at a given excitation wavelength, and well-resolved emission spectra with narrow bandwidths. Most common dye probes have low photobleaching thresholds, require different excitation wavelengths, and exhibit broad emission spectra. In contrast, quantum dots (QDs) exhibit relatively narrow emission band widths of 20 to 30 nm (full width at half maximum (FWHM)) under single-wavelength excitation, but they can suffer from cytotoxicity in vivo, fluorescence intermittency, and limited distinguishable features in the emission spectra. Moreove, particles with a narrow size distribution (ca. 5%) often require stringent synthesis conditions. The single emission peaks resulting from excitation of QDs of similar sizes make spectral interpretation difficult when overlapping spectral features become predominant. As an alternative to dye molecules and QDs, lanthanidedoped nanoparticles have been suggested as a promising new class of fluorescent probes. They show superior chemical and optical properties, including low toxicity, large effective Stokes shifts, sharp emission band widths of 10 to 20 nm (FWHM), as well as high resistance to photobleaching, blinking, and photochemical degradation. More importantly, in contrast to single emission peaks observed for QDs, the Ln-doped nanoparticles generally show a distinct set of sharp emission peaks arising from f–f orbital electronic transitions. The multiple-peak patterns should provide spectroscopic fingerprints, which are particularly useful for accurate interpretation in the event of overlapping emission spectra. These unique properties, coupled with sizeand shape-independent luminescent phenomena, make Lndoped nanoparticles highly suitable fluorescent probes for multicolor labeling applications. Herein, we present two complementary approaches (tuning emission wavelength and relative intensity) to emission color modulation by singlewavelength excitation based upon (Ln, P)-doped YVO4 hostlattice sensitized nanoparticle systems. The YVO4 nanoparticles doped with Ln and phosphorous ions were synthesized in aqueous media in the presence of polyvinylpyrrolidone (PVP). The metal-chelating PVP molecules stabilize the Ln ions and control the growth of nanoparticles upon reaction with [VO4] 3 and [PO4] 3

Up- and Down-Conversion Cubic Zirconia and Hafnia Nanobelts†

Abstract: One-dimensional (1D) metal oxide nanomaterials, such as zinc oxide (ZnO) nanowires and nanobelts (or nanoribbons), have recently attracted immense attention due to their sizeand shape-dependent optical, mechanical, and electronic properties. In stark contrast, investigations of 1D zirconia (ZrO2) and hafnia (HfO2) nanomaterials remain unexploited largely because of the formidable challenges associated with the fabrication of these structures with controlled dimensions and crystal phases. ZrO2 and HfO2 materials typically exhibit three primary polymorphs (monoclinic, tetragonal, and cubic) and have important technological applications as catalyst supports, oxygen detectors, hightemperature fuel cell electrolytes, gate dielectric in metaloxide semiconductor devices, and optical waveguides. Apart from a few rare examples of rod-like polycrystalline structures formed via porous alumina templates or by using an inverse microemulsion technique, most of the ZrO2 nanomaterials obtained thus far are best classified as nanoparticles and thin films. Here, we introduce a direct and scalable approach, based upon a thermal decomposition method under normal atmospheric pressure, for growing well-defined single-crystalline cubic ZrO2 and HfO2 nanobelts with controllable structural compositions and novel optical properties. To the best of our knowledge, these nanomaterials provide the first evidence of ZrO2 and HfO2 crystals with belt-like morphology. In a typical synthesis of the ZrO2 precursors, a solution of ZrCl4 (1.6 g, 7 mmol) and YCl3 6H2O (0.3 g, 1 mmol) in ethanol (10mL) was first treated with sodium hydroxide (1.5 g, 38 mmol) to yield a viscous gel mixture. The mixture was transferred into a 15mL Teflon-lined autoclave and heated at 140 8C for 24 h. Upon cooling the resulting precipitate was

Large reversible magnetocaloric effect in TbCoC(2) in low magnetic field

Abstract: A large reversible negative magnetic-entropy change ΔSM has been observed in TbCoC2, accompanied by a second-order phase transition at 28K. The maximum value of −ΔSM is 15.3Jkg−1K−1 at 30K for a magnetic-field change from 0to5T, with the refrigerant capacity of 354Jkg−1. In particular, also the large −ΔSMmax of 7.8Jkg−1K−1, is obtained for a small field change from 0to2T. The large reversible ΔSM and the high reversible refrigerant capacity in low magnetic field indicate that TbCoC2 may be a promising candidate for magnetic refrigeration at low temperatures.

Electromagnetic-wave absorption properties of FeCo nanocapsules and coral-like aggregates self-assembled by the nanocapsules

Abstract: FeCo nanocapsules with FeCo alloy as core and amorphous Al(2)O(3) as shell have been synthesized by a modified arc-discharge technique Three-dimensional coral-like aggregates are self-assembled by the nanocapsules in the arc-discharge process The FeCo nanocapsules are ferromagnetic at room temperature The electromagnetic-wave absorption properties of FeCo nanocapsules were investigated in the frequency range from 2 to 18 GHz A reflection loss exceeding -20 dB was obtained in the frequency range of 52-159 GHz for absorber thicknesses of 2-4 mm An optimal reflection loss of -448 dB was reached at 128 GHz for an absorber thickness of 3 mm As a result, these FeCo nanocapsules may be applied in high-frequency electromagnetic-wave absorption (C) 2008 American Institute of Physics [DOI: 101063/12982411]

Integrated Nanostructures and Nanodevices Fabricated by Dip-Pen Nanolithography

Abstract: T he ability to tailor the chemical composition and structure of a surface at the nanometer length scale is essential for fabricating novel nanomaterials, understanding underlying nano-science and engineering, and developing integrated systems for demanding applications. Dip-pen nanolithography (DPN), based upon an atomic force microscope, has recently evolved as a unique tool that allows one to routinely pattern an extraordinary array of materials onto all manner of surfaces at the sub-100-nm to many-micrometer length scale. This chapter briefly reviews the rapid growth of the research field of DPN with particular emphasis on biological applications.