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 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This paper reports a simple, one-pot, template-free synthesis of flower-like Au nanoparticles (three-dimensional branched nanoparticles with more than 10 tips) with high yield and good size monodispersity at room temperature. The size of the Au nanoflowers could be tuned by controlling the composition of the starting reaction mixture. The key synthesis strategy was to use a common Good's buffer, HEPES, as a weak reducing and particle stabilizing agent to confine the growth of the Au nanocrystals in the special reaction region of limited ligand protection (LLP). Time-course measurements by UV-vis spectroscopy and TEM were used to follow the reaction progress and the evolution of the flower-like shape. The Au nanoflowers exhibited strong surface-enhanced effects which were utilized in the design of an efficient, stable, and nontoxic Raman-active tag for in vivo applications.
ACS Nano 2008 Dec 23
PMID:The synthesis of SERS-active gold nanoflower tags for in vivo applications. 1920 81

PbS quantum dots (PbS QDs) were prepared on the inside and outside surfaces of TiO(2) nanotubes by using thiolactic acid as an organic linker. The sizes of PbS QDs were controlled by employing a dip coating process to anchor the PbS QDs onto the TiO(2) nanotubes. The PbS QDs with diameters of 2-10 nm were obtained by adjusting the concentration of thiolactic acid. TiO(2) nanotubes with PbS QDs located only inside the nanotubes were prepared by first coating the tubes with the double-chain cationic surfactant DDAB. The PbS QDs supported on TiO(2) nanotubes were characterized by TEM, as well as Raman, FT-IR, and UV-vis spectroscopy.
ACS Nano 2008 Aug
PMID:Fabrication of PbS quantum dot doped TiO2 nanotubes. 1920 72

Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.
ACS Nano 2008 Sep 23
PMID:Reversible clustering of pH- and temperature-responsive Janus magnetic nanoparticles. 1920 18

Diatoms are single-celled algae that make silica shells or frustules with intricate nanoscale features imbedded within periodic two-dimensional pore arrays. A two-stage photobioreactor cultivation process was used to metabolically insert titanium into the patterned biosilica of the diatom Pinnularia sp. In Stage I, diatom cells were grown up on dissolved silicon until silicon starvation was achieved. In Stage II, soluble titanium and silicon were continuously fed to the silicon-starved cell suspension (approximately 4 x 10(5) cells/mL) for 10 h. The feeding rate of titanium (0.85-7.3 micromol Ti L(-1) h(-1)) was designed to circumvent the precipitation of titanate in the liquid medium, and feeding rate of silicon (48 micromol Si L(-1) h(-1)) was designed to sustain one cell division. The addition of titanium to the culture had no detrimental effects on cell growth and preserved the frustule morphology. Cofeeding of Ti and Si was required for complete intracellular uptake of Ti. The maximum bulk composition of titanium in the frustule biosilica was 2.3 g of Ti/100 g of SiO(2). Intact biosilica frustules were isolated by treatment of diatom cells with SDS/EDTA and then analyzed by TEM and STEM-EDS. Titanium was preferentially deposited as a nanophase lining the base of each frustule pore, with estimated local TiO(2) content of nearly 80 wt %. Thermal annealing in air at 720 degrees C converted the biogenic titanate to anatase TiO(2) with an average crystal size of 32 nm. This is the first reported study of using a living organism to controllably fabricate semiconductor TiO(2) nanostructures by a bottom-up self-assembly process.
ACS Nano 2008 Oct 28
PMID:Metabolic insertion of nanostructured TiO2 into the patterned biosilica of the diatom Pinnularia sp. by a two-stage bioreactor cultivation process. 1920 57

The synthesis and characterization of colloidal mesoporous silica (CMS) functionalized with vinyl-, benzyl-, phenyl-, cyano-, mercapto-, aminopropyl- or dihydroimidazole moieties is reported. Uniform mesoporous particles ranging in size from 40 to 150 nm are generated in a co-condensation process of tetraethylorthosilicate (TEOS) and organotriethoxysilanes (RTES) in alkaline aqueous media containing triethanolamine (TEA) in combination with cetyltrimethylammonium chloride (CTACl) serving as a structure-directing agent. The materials are obtained as colloidal suspensions featuring long-term stability after template removal by ion exchange with an ethanolic solution of ammonium nitrate or HCl. The spherical particles exhibit a wormlike pore system with defined pore sizes and high surface areas. Samples are analyzed by a number of techniques including TEM, SEM, DLS, TGA, Raman, and cross-polarized (29)Si-MAS NMR spectroscopy, as well as nitrogen sorption measurements. We demonstrate that co-condensation and grafting methods result in similar changes in the nitrogen adsorption behavior, indicating a successful internal lining of the pores with functional groups through both procedures.
ACS Nano 2008 Apr
PMID:Colloidal suspensions of functionalized mesoporous silica nanoparticles. 1920 12

This paper describes the synthesis and electrical properties of self-organized Sb-, Nb-, and Ta-doped SnO(2) thin films with adjustable doping levels. These transparent conducting oxides (TCOs) were prepared using a poly(ethylene-co-butylene)-b-poly(ethylene oxide) diblock copolymer as well as a novel polyisobutylene-b-poly(ethylene oxide) as organic templates. All samples are highly crystalline and have ordered cubic pore-solid architectures after removal of the polymer template by calcination; however, the electrical conductivity is not identical. The films are characterized by a combination of small- and wide-angle X-ray diffraction/scattering, SEM/TEM imaging, and X-ray photoelectron spectroscopy. Resistivity measurements conducted on the mesoporous frameworks show that the electrical properties strongly depend on both the degree of crystallinity and the elemental makeup. Considerable enhancements of the electrical properties result when the films are doped with antimony and treated in N(2) at elevated temperatures. Such TCO materials show electrical resistivities which are--despite the mesoporous morphology--only 1 order of magnitude higher than reported values for dense Sb-doped SnO(2) films.
ACS Nano 2009 Jun 23
PMID:Ordered mesoporous Sb-, Nb-, and Ta-doped SnO2 thin films with adjustable doping levels and high electrical conductivity. 1943 71

We present a model to calculate particle size distributions (PSDs) of colloidal ZnO nanoparticles from their absorbance spectra. Using literature values for the optical properties of bulk ZnO and correlating the measurement wavelengths in the UV-visible regime with distinct particle sizes by a tight binding model (TBM), an algorithm deconvolutes the absorbance spectra into contributions from size fractions. We find an excellent agreement between size distributions determined from TEM images and the calculated PSDs. For further validation, bimodal PSDs have been investigated and an approach to determine not only particle size but also solid concentration is introduced. We will show the applicability of our model by the determination of temperature-dependent ripening rates, which enables the calculation of solubilities, surface tensions, and the activation enthalpy of ripening. In principle, our methodology is applicable to different semiconductor nanoparticles in various solvents as long as their bulk properties are known and scattering is negligible.
ACS Nano 2009 Jul 28
PMID:Analysis of optical absorbance spectra for the determination of ZnO nanoparticle size distribution, solubility, and surface energy. 1950 65

The effect of bulk network density on the extent of quantum confinement (probed by optical band gap) in CdSe quantum dot gels is evaluated. The CdSe gels were produced from controlled removal of surface thiolate ligands from CdSe quantum dots by adding 3% tetranitromethane. Two main techniques were employed to systematically vary the bulk density. First, different amounts of oxidizing agent were added to change the monolith density of the wet gel, followed by supercritical CO(2) drying to yield CdSe aerogels with different bulk densities. Experimental results suggest that a gradual and almost linear band gap decrease is observed when increasing the bulk density at the aerogel level. The fact that quantum confinement effects are largely preserved in aerogel constructs is consistent with SAXS data revealing the fractal nature of the network. Second, for a constant amount of oxidant, different drying techniques were used to yield CdSe gels with a larger density variation: aerogels (supercritical CO(2) dried), ambigels (hexane dried), and xerogels (acetone dried). A nonlinear trend for band gap decrease was found when comparing CdSe aerogels, ambigels, and xerogels, and the more dense ambi- and xerogels have broader absorption edges, suggestive of resonance transfer effects due to dipole-dipole interactions in non-homogeneous interacting systems. This is attributed to increased aggregation in the denser constructs (supported by TEM and SAXS data). Together, these data suggest that highly porous architectures, such as aerogels, are best suited for maintaining localized quantum confinement effects in 3D connected nanoparticle networks.
ACS Nano 2009 Jul 28
PMID:Tuning the optical band gap of quantum dot assemblies by varying network density. 1957 42

Amine monofunctional gold nanoparticles (1-AuNPs) were synthesized by employing a solid-supported technique and pH-switchable pseudorotaxane formation. Purification was repeatedly facilitated using crown ether peripherally coated superparamagnetic iron oxide microspheres to yield the monofunctional gold nanoparticles in excellent yield. The product and its related intermediate superstructures were characterized by IR and X-ray photoelectron spectroscopies. Novel supramolecular dimers and trimers were prepared by titrating the 1-AuNPs with bisDB24C8 and trisDB24C8 at different ratios. UV/visible absorption spectroscopic analyses of the supramolecular dimer and trimer solutions, which were formed by mixing their separate components in different ratios, indicated the gradual appearance of two distinct plasmonic resonance bands at 620 and approximately 700 nm. Furthermore, TEM images of the dimers revealed a significant amount of dimer pairs on the surface, while the TEM images of the trimers demonstrated the presence of both dimers and trimers. The trimers appeared as triangular or near-linear shapes.
ACS Nano 2009 Aug 25
PMID:Discrete functional gold nanoparticles: hydrogen bond-assisted synthesis, magnetic purification, supramolecular dimer and trimer formation. 1962 79

A general method is described for the deposition of metal nanoparticles selectively either inside or outside of carbon nanotubes (CNTs). The method is based on the difference in the interface energies of organic and aqueous solutions with the CNT surface. Because of their lipophilic character, the organic solvent better wets the surface of the nanotubes compared to water and penetrates into the inner volume. The precise control of the volume of each phase allows filling the CNT with the organic phase and covering its outer surface with the aqueous one. Hence, metal nanoparticles can be put with high selectivity either inside or outside the CNT, just by choosing in which solvent the metal precursor is dissolved. SEM, TEM, and 3D-TEM investigations show that a selectivity in localization close to 75% can be reached by this technique. The nanoparticles are homogeneously dispersed and present a narrow size distribution, centered on 5 nm. In this way, one can decorate either the inner or the outer surface of open CNTs, without the need of discriminating the diameter of the opening and without any further step of functionalization than a treatment with nitric acid.
ACS Nano 2009 Aug 25
PMID:Selective deposition of metal nanoparticles inside or outside multiwalled carbon nanotubes. 1970 19


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