Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

We report the synthesis of high magnetic moment CoFe nanoparticles via the diffusion of Co and Fe in core/shell structured Co/Fe nanoparticles. In an organic solution, Co nanoparticles were coated with a layer of Fe to form a Co/Fe core/shell structure. Further raising the solution temperature led to inter-diffusion of Co and Fe and formation of CoFe alloy nanoparticles. These nanoparticles have high saturation magnetization of up to 192 emu/g CoFe and can be further stabilized by thermal annealing at 600 °C. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. These two authors made an equal contribution to the work.     

Isolation of single-walled carbon nanotube enantiomers by density differentiation

Current methods of synthesizing single-walled carbon nanotubes (SWNTs) result in racemic mixtures that have impeded the study of left- and right-handed SWNTs. Here we present a method of isolating different SWNT enantiomers using density gradient ultracentrifugation. Enantiomer separation is enabled by the chiral surfactant sodium cholate, which discriminates between left- and right-handed SWNTs and thus induces subtle differences in their buoyant densities. This sorting strategy can be employed for simultaneous enrichment by handedness and roll-up vector of SWNTs having diameters ranging from 0.7 to 1.5 nm. In addition, circular dichroism of enantiomer refined samples enables identification of high-energy optical transitions in SWNTs. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Control of aggregate size of polyethyleneimine-coated magnetic nanoparticles for magnetofection

Using magnetic nanoparticles to enhance gene transfection, a recently developed technique termed magnetofection, has been shown to be a powerful technology in gene delivery. The most widely used magnetic nanoparticles in this area are those coated with polyethyleneimine, which is a well known nonviral transfection agent. In this article, we report methods to control the aggregate size of polyethyleneimine-coated magnetite particles. These particles were then used to enhance transfection of green fluorescent protein (GFP) into NIH 3T3 cells in vitro. We find that the aggregate size of the particles has a great effect on their performance in magnetofection, with less aggregated magnetic particles being more effective in enhancing the gene transfection. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Size-dependent joule heating of gold nanoparticles using capacitively coupled radiofrequency fields

Capacitively coupled shortwave radiofrequency fields (13.56 MHz) resistively heat low concentrations (∼1 ppm) of gold nanoparticles with a thermal power dissipation of ∼380 kW/g of gold. Smaller diameter gold nanoparticles (< 50 nm) heat at nearly twice the rate of larger diameter gold nanoparticles (≥50 nm), which is attributed to the higher resistivity of smaller gold nanostructures. A Joule heating model has been developed to explain this phenomenon and provides critical insights into the rational design and engineering of nanoscale materials for noninvasive thermal therapy of cancer. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. These two authors made an equal contribution to the work.     

Odako growth of dense arrays of single-walled carbon nanotubes attached to carbon surfaces

A novel process is demonstrated whereby dense arrays of single-walled carbon nanotubes (SWNT) are grown directly at the interface of a carbon material or carbon fiber. This growth process combines the concepts of SWNT tip growth and alumina-supported SWNT base growth to yield what we refer to as “odako” growth. In odako growth, an alumina flake detaches from the carbon surface and supports catalytic growth of dense SWNT arrays at the tip, leaving a direct interface between the carbon surface and the dense SWNT arrays. In addition to being a new and novel form of SWNT array growth, this technique provides a route toward future development of many important applications for dense aligned SWNT arrays. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Nanotrains and self-assembled two-dimensional arrays built from carboranes linked by hydrogen bonding of dipyridones

The strong hydrogen bonding ability of 2-pyridones were exploited to build nanotrains on surfaces. Carborane wheels on axles difunctionalized with 2-pyridone hydrogen bonding units were synthesized and displayed spontaneous formation of linear nanotrains by self-assembly on SiO₂ or mica surfaces. Imaging using atomic force microscopy confirmed linear formations with lengths up to 5 μm and heights within the range of the molecular height of the carborance-tipped axles. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Au-Ag alloy nanoporous nanotubes

Metallic nanostructures with hollow interiors or tailored porosity represent a special class of attractive materials with intriguing chemicophysical properties. This paper presents the fabrication of a new type of metallic nanoporous nanotube structure based on a facile and effective combination of nanocrystal growth and surface modification. By controlling the individual steps involved in this process, such as nanowire growth, surface modification, thermal diffusion, and dealloying, one-dimensional (1-D) metallic nanostructures can be prepared with tailored structural features and pre-designed functionalities. These tubular and porous nanostructures show distinct optical properties, such as tunable absorption in the near-infrared region, and enhanced capability for electrochemiluminescence signal amplification, which make them particularly desirable as novel 1-D nanocarriers for biomedical, drug delivery and sensing applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Synthesis of monodisperse CdS nanorods catalyzed by Au nanoparticles

Semiconductor nanocrystals (dots, rods, wires, etc.) exhibit a wide range of electrical and optical properties that differ from those of the corresponding bulk materials. These properties depend on both nanocrystal size and shape. Compared with nanodots, nanorods have an additional degree of freedom, the length or aspect ratio, and reduced symmetry, which leads to anisotropic properties. In this paper, we report the Au nanoparticlecatalyzed colloidal synthesis of monodisperse CdS nanorods. Based on systematic high resolution transmission electron microscopy studies, we propose a growth mechanism for these nanorods. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Magnetic field-induced solvothermal synthesis of one-dimensional assemblies of Ni-Co alloy microstructures

One-dimensional magnetic Ni-Co alloy microwires with different microstructures and differently shaped building blocks including spherical particles, multilayer stacked alloy plates, and alloy flowers, have been synthesized by an external magnetic field-assisted solvothermal reaction of mixtures of cobalt(II) chloride and nickel(II) chloride in 1, 2-propanediol with different NaOH concentrations. By adjusting the experimental parameters, such as precursor concentration and Ni/Co ratio, Ni-Co alloy chains with uniform diameters in the range 500 nm to 1.3 μm and lengths ranging from several micrometers to hundreds of micrometers can be obtained. A mechanism of formation of the one-dimensional assemblies of magnetic Ni-Co microparticles in a weak external magnetic field is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Synthesis and characterization of bionanoparticle—Silica composites and mesoporous silica with large pores

A sol-gel process has been developed to incorporate bionanoparticles, such as turnip yellow mosaic virus, cowpea mosaic virus, tobacco mosaic virus, and ferritin into silica, while maintaining the integrity and morphology of the particles. The structures of the resulting materials were characterized by transmission electron microscopy, small angle X-ray scattering, and N₂ adsorption-desorption analysis. The results show that the shape and surface morphology of the bionanoparticles are largely preserved after being embedded into silica. After removal of the bionanoparticles by calcination, mesoporous silica with monodisperse pores, having the shape and surface morphology of the bionanoparticles replicated inside the silica, was produced,. This study is expected to lead to both functional composite materials and mesoporous silica with structurally well-defined large pores. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

PtAu bimetallic heteronanostructures made by post-synthesis modification of Pt-on-Au nanoparticles

Bimetallic PtAu heteronanostructures have been synthesized from Pt-on-Au nanoparticles, which were made from platinum acetylacetonate and gold nanoparticles. Using the Pt-on-Au nanoparticles as precursors, Ptsurface rich PtAu bimetallic heteronanostructures can be produced through controlled thermal treatments, as confirmed by field emission high-resolution transmission electron microscopy (HR-TEM) and elemental mapping using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). Oxidation of formic acid was used as a model reaction to demonstrate the effects of varying composition and surface structure on the catalytic performance of PtAu bimetallic nanostructures. Cyclic voltammetry (CV) showed that these carbon-supported PtAu heteronanostructures were much more active than platinum in catalyzing the oxidation of formic acid, judging by the mass current density. The results showed that postsynthesis modification can be a very useful approach to the control of composition distributions in alloy nanostructures. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Two distinct fluorescent quantum clusters of gold starting from metallic nanoparticles by pH-dependent ligand etching

Two fluorescent quantum clusters of gold, namely Au₂₅ and Au₈, have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4–5 nm core diameter by etching with excess glutathione. While etching at pH ∼3 yielded Au₂₅, that at pH 7–8 yielded Au₈. This is the first report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fluorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions

We propose a simple method for the efficient and rapid synthesis of one-dimensional hematite (α-Fe₂O₃) nanostructures based on electrical resistive heating of iron wire under ambient conditions. Typically, 1–5 μm long α-Fe₂O₃ nanowires were synthesized on a time scale of seconds at temperatures of around 700 ° ⊂. The morphology, structure, and mechanism of formation of the nanowires were studied by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman techniques. A nanowire growth mechanism based on diffusion of iron ions to the surface through grain boundaries and to the growing wire tip through stacking fault defects and due to surface diffusion is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

A nano- and micro- integrated protein chip based on quantum dot probes and a microfluidic network

A novel nano- and micro-integrated protein chip (NMIPC) that can detect proteins with ultrahigh sensitivity has been fabricated. A microfluidic network (μFN) was used to construct the protein chips, which allowed facile patterning of proteins and subsequent biomolecular recognition. Aqueous phase-synthesized, water-soluble fluorescent CdTe/CdS core-shell quantum dots (aqQDs), having high quantum yield and high photostability, were used as the signaling probe. Importantly, it was found that aqQDs were compatible with microfluidic format assays, which afforded highly sensitive protein chips for cancer biomarker assays. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy

We introduce voltage-contrast scanning electron microscopy (VC-SEM) for visual characterization of the electronic properties of single-walled carbon nanotubes. VC-SEM involves tuning the electronic band structure and imaging the potential profi le along the length of the nanotube. The resultant secondary electron contrast allows to distinguish between metallic and semiconducting carbon nanotubes and to follow the switching of semiconducting nanotube devices, as confi rmed by in situ electrical transport measurements. We demonstrate that high-density arrays of individual nanotube devices can be rapidly and simultaneously characterized. A leakage current model in combination with fi nite element simulations of the device electrostatics is presented in order to explain the observed contrast evolution of the nanotube and surface electrodes. This work serves to fill a void in electronic characterization of molecular device architectures. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Role of catalysts in the surface synthesis of single-walled carbon nanotubes

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.      

Synthesis and Ex situ doping of ZnTe and ZnSe nanostructures with extreme aspect ratios

We report synthesis windows for growth of millimeter-long ZnTe nanoribbons and ZnSe nanowires using vapor transport. By tuning the local conditions at the growth substrate, high aspect ratio nanostructures can be synthesized. A Cu-ion immersion doping method was applied, producing strongly p-type conduction in ZnTe and ionic conduction in ZnSe. These extreme aspect ratio wide-bandgap semiconductors have great potential for high density nanostructured optoelectronic circuits.      

Formation of Na0.44MnO2 nanowires via stress-induced splitting of birnessite nanosheets

High aspect ratio Na_0.44MnO₂ nanowires with a complex one-dimensional (1-D) tunnel structure have been synthesized. We found that the reaction went through layered birnessite nanosheet intermediates, and that their conversion to the final product involved splitting of the nanosheets into nanowires. Based on our observations, a stress-induced splitting mechanism for conversion of birnessite nanosheets to Na_0.44MnO₂ nanowires is proposed. The final and intermediate phases show topotaxy with 〈001〉_f // 〈020〉_b or 〈110〉_b where f represents the final Na_0.44MnO₂ phase and b the intermediate birnessite phase. As a result of their high surface areas, the nanowires are efficient catalysts for the oxidation of pinacyanol chloride dye. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Direct growth of enclosed ZnO nanotubes

To date, wet syntheses of single-crystalline ZnO micro- and nanotubes have been carried out using a two-step indirect approach in which a selective dissolution step is required in order to create the vacant space in the tubular structures. In this work, we develop a direct growth process for preparation of single-crystal ZnO nanotubes and nanorods. We also report that a concave shaped crystal growth front is generally reactive and offers a large surface area for matter deposition during rapid expansion of unidirectional nanomaterials. Depending on the degree of supersaturation of nutrients in solution, the concave growth front can either remain unaltered or undergo a concave-to-convex transformation, leading to the growth of solid nanorods and/or hollow nanotubes. The observed volume inversion should, in principle, also be applicable to the nanoarchitecture of other one-dimensional wurtzite structured nanomaterials, although individual sets of synthesis parameters need to be developed for each target material. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Carbon nanotubes inhibit the hemolytic activity of the pore-forming toxin pyolysin

Functionalized carbon nanotubes have already demonstrated great biocompatibility and potential for drug delivery. We have synthesized acid oxidized and non-covalently PEGlyated single-walled carbon nanotubes (SWNTs), which were previously prepared for drug delivery purposes, and explored their potential for detoxification in the bloodstream. Our investigations of the binding of SWNTs to a pore-forming toxin pyolysin show that SWNTs prevented toxin-induced pore formation in the cell membrane of human red blood cells. Quantitative hemolysis assay and scanning electron microscopy were used to evaluate the inhibition of hemolytic activity of pyolysin. According to Raman spectroscopy data, human red blood cells, unlike HeLa cells, did not internalize oxidized SWNTs. Molecular modeling and circular dichroism measurements were used to predict the 3-D structure of pyolysin (domain 4) and its interaction with SWNTs. The tryptophan-rich hydrophobic motif in the membrane-binding domain of pyolysin, a common construct in a large family of cholesterol-dependent cytolysins, shows high affinity for SWNTs. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com