Ambient large-scale template-mediated synthesis of high-aspect ratio single-crystalline, chemically doped rare-earth phosphate nanowires for bioimaging

Lanthanide ion-doped GdPO4 nanorods with dual-modal bio-optical and magnetic resonance imaging properties

Here, dual-modal bioprobes for combined optical and magnetic resonance (MR) imaging are reported. Gadolinium orthophosphate (GdPO(4)) nanorods co-doped with light-emitting lanthanide ions have been successfully prepared through a hydrothermal method. An efficient downconversion luminescence from Ce/Tb or Eu doped GdPO(4) nanorods and upconversion luminescence from Yb/Er co-doped GdPO(4) nanorods are observed, respectively, which offers the optical modality for the nanoprobes. Notably, we first report the upconversion phenomenon based on the GdPO(4) matrix under 980 nm near infrared irradiation. The possibility of using these nanoprobes with downconversion and upconversion luminescent emissions for optical cell imaging is also demonstrated. Furthermore, these Gd(3+)-containing nanophosphors show good positive signal-enhancement ability when performed under a 4.7 T MR imaging scanner, indicating they have potential as T(1) MR imaging contrast agents. Thus, nanoprobes based on GdPO(4) nanophosphors are shown to provide the dual modality of optical and MR imaging.

Optically stable biocompatible flame-made SiO2-coated Y2O3:Tb3+ nanophosphors for cell imaging

Nanophosphors are light-emitting materials with stable optical properties that represent promising tools for bioimaging. The synthesis of nanophosphors, and thus the control of their surface properties, is, however, challenging. Here, flame aerosol technology is exploited to generate Tb-activated Y(2)O(3) nanophosphors (∼25 nm) encapsulated in situ by a nanothin amorphous inert SiO(2) film. The nanocrystalline core exhibits a bright green luminescence following the Tb(3+) ion transitions, while the hermetic SiO(2)-coating prevents any unspecific interference with cellular activities. The SiO(2)-coated nanophosphors display minimal photobleaching upon imaging and can be easily functionalized through surface absorption of biological molecules. Therefore, they can be used as bionanoprobes for cell detection and for long-term monitoring of cellular activities. As an example, we report on the interaction between epidermal growth factor (EGF)-functionalized nanophosphors and mouse melanoma cells. The cellular uptake of the nanophosphors is visualized with confocal microscopy, and the specific activation of EGF receptors is revealed with biochemical techniques. Altogether, our results establish SiO(2)-coated Tb-activated Y(2)O(3) nanophosphors as superior imaging tools for biological applications.

Cytotoxicity and cell imaging potentials of submicron color-tunable yttria particles

Increased demand of environment protection encouraged scientists to design products and processes that minimize the use and generation of hazardous substances. This work presents comprehensive result of large-scale fabrication and investigation of red-to-green tunable submicron spherical yttria particles codoped with low concentrations of Eu(+3) and Tb(+3). The color emission of synthesized particles can be precisely tuned from red to green by simple variation of Tb/Eu ratio and excitation wavelength. The Tb/Eu-codoped Y(2)O(3) particles did not adversely affect the viability of L-929 fibroblastic cells at concentrations less than 62.5 ppm. Through internalization and wide distribution inside the cells, Tb/Eu codoped Y(2)O(3) particles with intense bright green or red fluorescence rendered cell imaging to be possible. The high brightness, excellent stability, low-toxicity, and imaging capability along with fine color-tunability of synthesized particles enable to find promising application in various areas.

Highly enhanced electrocatalytic oxygen reduction performance observed in bimetallic palladium-based nanowires prepared under ambient, surfactantless conditions

We have employed an ambient, template-based technique that is simple, efficient, and surfactantless to generate a series of bimetallic Pd(1-x)Au(x) and Pd(1-x)Pt(x) nanowires with control over composition and size. Our as-prepared nanowires maintain significantly enhanced activity toward oxygen reduction as compared with commercial Pt nanoparticles and other 1D nanostructures, as a result of their homogeneous alloyed structure. Specifically, Pd(9)Au and Pd(4)Pt nanowires possess oxygen reduction reaction (ORR) activities of 0.49 and 0.79 mA/cm(2), respectively, which are larger than the analogous value for commercial Pt nanoparticles (0.21 mA/cm(2)). In addition, core-shell Pt~Pd(9)Au nanowires have been prepared by electrodepositing a Pt monolayer shell and the corresponding specific, platinum mass, and platinum group metal mass activities were found to be 0.95 mA/cm(2), 2.08 A/mg(Pt), and 0.16 A/mg(PGM), respectively. The increased activity and catalytic performance is accompanied by improved durability toward ORR.

Green, Silica-Coated Monoclinic Y(2)O(3):Tb(3+) Nanophosphors: Flame Synthesis and Characterization

Silica-coated and uncoated, Tb-doped (1-5 at % Tb) Y(2)O(3) green nanophosphors were made, for the first time, in a single step by flame aerosol technology with controlled crystal phase (cubic and monoclinic) and morphology. The nanophosphors were characterized by X-ray diffraction, N(2) adsorption, high resolution electron microscopy, and photoluminescence spectroscopy. The monoclinic crystal structure of Y(2)O(3):Tb(3+) nanophosphors favors the electric dipole (5)D(4) → (7)F(5) transition driving their green phosphorescence. The phosphorescence of the SiO(2)-coated monoclinic Y(2)O(3):Tb(3+) nanophosphors is lower than the uncoated ones. Upon annealing these nanophosphors, they were transformed from monoclinic to cubic and their phosphorescence was reduced. This further indicates the superior performance of the monoclinic crystal phase for the electric dipole transitions of Tb(3+) ions.

Ambient surfactantless synthesis, growth mechanism, and size-dependent electrocatalytic behavior of high-quality, single crystalline palladium nanowires

In this report, we utilize the U-tube double diffusion device as a reliable, environmentally friendly method for the size-controlled synthesis of high-quality, single crystalline Pd nanowires. The nanowires grown in 200 and 15 nm polycarbonate template pores maintain diameters of 270 ± 45 nm and 45 ± 9 nm, respectively, and could be isolated either as individual nanowires or as ordered free-standing arrays. The growth mechanism of these nanowires has been extensively explored, and we have carried out characterization of the isolated nanowires, free-standing nanowire arrays, and cross sections of the filled template in order to determine that a unique two-step growth process predominates within the template pores. Moreover, as-prepared submicrometer and nanosized wires were studied by comparison with ultrathin 2 nm Pd nanowires in order to elucidate the size-dependent trend in oxygen reduction reaction (ORR) electrocatalysis. Subsequently, the desired platinum monolayer overcoating was reliably deposited onto the surface of the Pd nanowires by Cu underpotential deposition (UPD) followed by galvanic displacement of the Cu adatoms. The specific and platinum mass activity of the core-shell catalysts was found to increase from 0.40 mA/cm(2) and 1.01 A/mg to 0.74 mA/cm(2) and 1.74 A/mg as the diameter was decreased from the submicrometer size regime to the ultrathin nanometer range.

Photoluminescence, cytotoxicity and in vitro imaging of hexagonal terbium phosphate nanoparticles doped with europium

Luminescent TbPO4 nanoparticles were synthesized via a citric-acid-mediated hydrothermal route. Eu3+ doping of TbPO4 enables an efficient Tb3+-to-Eu3+ energy transfer, leading to a four-fold increase of the absolute emission quantum yield (QY), compared to that of undoped TbPO4. To check the potential of biological use, we conducted in vitro biological experiments on human cervical carcinoma HeLa cells incubated with TbPO4:Eu nanoparticles. TbPO4:Eu nanoparticles can be successfully internalized into the cells, and they show bright intracellular luminescence and very low cytotoxicity. Photoluminescence intensity dependence upon time demonstrates that Eu3+-doped TbPO4 nanoparticles are highly resistant to photobleaching. Our present work represents a demonstration of the use of rare-earth-based nanocrystals as a biological labeling agent because they combine several advantages including high emission quantum yield, long luminescence lifetime, low cytotoxicity and high photostability.

Color-tunable nanophosphors by co-doping flame-made Y2O3 with Tb and Eu

Rare-earth phosphors with tunable optical properties are used in display panels and fluorescent lamps and have potential applications in lasers and bio-imaging. Here, non-aggregated Y2O3 nanocrystals either doped with Tb3+ (1-5 at%) or co-doped with Tb3+ (2 at%) and Eu3+ (0.1-2 at%) ions are made in one-step by scalable flame spray pyrolysis. The morphology of these nanophosphors is investigated by X-ray diffraction, electron microscopy and N2 adsorption while their optical properties are monitored by photoluminescent spectroscopy. When yttria nanocrystals are doped with terbium, a bright green emission is obtained at an optimum Tb-content of 2 at%. When, however, europium is added, the emission color of these Tb-doped yttria nanophosphors can be tuned precisely from green to red depending on the Tb/Eu ratio. Furthermore, energy-transfer from Tb3+ to Eu3+ is observed, thus allowing the control of the excitation spectra of the co-doped nanophosphors.

Remarkably enhanced photoluminescence of hexagonal GdPO4.nH2O:Eu with decreasing size

The hexagonal rhabdophane-type GdPO(4) hydrate (GdPO(4).nH(2)O) was synthesized via a simple hydrothermal process. The size and morphology of the products can be tunable by adjusting the pH of reaction systems through the addition of aqueous NaOH. The nanorods with a width of 50-100 nm and a length of about 1 microm were obtained in the absence of NaOH (pH = 2), while a significant reduction of size (width: approximately 10 nm, length: approximately 50 nm) was observed for the product synthesized in the presence of NaOH (pH = 10). Surprisingly, the small-sized product exhibits a remarkably enhanced photoluminescence quantum yield and long excited state lifetime in comparison with those of the large-sized product. This abnormal luminescence phenomenon is discussed and explained. The EDS and XPS measurements revealed the presence of Na(+) in the small-sized samples. These Na(+) cations were probably bonded to the surface O(2-) dangling bonds, which thus reduces the number of surface defects that usually serve as the nonradiative energy transfer center channels. A considerable reduction of surface defect centers results in the increase of the emission efficiency and excited state lifetime in a small-sized sample. Obviously, the controlled synthesis of rare-earth-doped nanoparticles with a small size, but with relatively strong luminescence, is significant for their applications in the areas of technologies including optoelectronics, sensing and bioimaging.