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     

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.     

Biosynthesis of biocompatible cadmium telluride quantum dots using yeast cells

We demonstrate a simple and efficient biosynthesis method to prepare easily harvested biocompatible cadmium telluride (CdTe) quantum dots (QDs) with tunable fluorescence emission using yeast cells. Ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) confirm that the CdTe QDs are formed via an extracellular growth and subsequent endocytosis pathway and have size-tunable optical properties with fluorescence emission from 490 to 560 nm and a cubic zinc blende structure with good crystallinity. In particular, the CdTe QDs with uniform size (2-3.6 nm) are protein-capped, which makes them highly soluble in water, and in situ bio-imaging in yeast cells indicates that the biosynthesized QDs have good biocompatibility. This work provides an economic and environmentally friendly approach to synthesize highly fluorescent biocompatible CdTe QDs for bio-imaging and bio-labeling applications.      

Synthesis and purple-blue emission of antimony trioxide single-crystalline nanobelts with elliptical cross section

Single-crystalline orthorhombic antimony trioxide (Sb₂O₃) nanobelts with unique elliptical cross sections and purple-blue photoluminescence have been synthesized. The uniform Sb₂O₃ nanobelts are 400–600 nm in width, 20–40 nm in thickness at the center and gradually become thinner to form sharp edges sub-5 nm in size, tens of micrometers in length, and with [001] as the preferential growth direction. Self-assembly of tens of nanobelts into three-dimensional (3-D) flower-like nanostructures has been observed. Analysis was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The Sb₂O₃ nanobelts display intense purple-blue photoluminescence centred at 425 nm (∼2.92 eV). The successful synthesis of nanobelts with elliptical cross sections may cast new light on the investigation of the property differences between nanobelts with rectangular cross sections and those with other cross section geometries. The Sb₂O₃ nanobelts can be used as effective purple-blue light emitters and may also be valuable for future nanodevice design. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Sensitization of hydrothermally grown single crystalline TiO2 nanowire array with CdSeS nanocrystals for photovoltaic applications

An oriented array of electron transporting nanowires, grown directly on a transparent conductor constitutes an optimal architecture for efficient photovoltaic applications. In addition, semiconductor nanocrystals can work as efficient light absorbers because of their tunable optical properties. In this paper, we use an oriented array of TiO₂ nanowires grown directly on a transparent conductive electrode and subsequently sensitized with colloidally grown CdSeS nanocrystal quantum dots (QDs), using an efficient bi-linker assisted methodology, to demonstrate photovoltaic cells. Upon excitation with light, exciton dissociation takes place at the nanowire-nanocrystal interface, after which, electrons are transported to the fluorine-doped tin oxide (FTO) electrode via single-crystalline TiO₂ nanowire channels. We demonstrate that an ex situ ligand exchange of QDs followed by sensitization on oxygen-plasma treated TiO₂ nanowires results in enhanced loading of QDs, as compared to the in situ ligand exchange approach. An array of 1 μm long TiO₂ nanowire sensitized with CdSeS nanocrystals exhibits photovoltaic effects with a short-circuit current of 2–3 mA/cm², an open circuit voltage of 0.6–0.7 V and a fill factor of 52–65%, resulting in devices with efficiencies of up to 0.6%.      

Multicolor luminescent carbon nanoparticles: Synthesis, supramolecular assembly with porphyrin, intrinsic peroxidase-like catalytic activity and applications

Luminescent carbon nanoparticles (CNPs) are newcomers to the world of nanomaterials and have shown great impact in health and environmental applications as well as being promising building blocks for future nanodevices because of their fascinating photoluminescence and potential to serve as nontoxic replacements for traditional heavy-metals-based quantum dots. Herein, fluorescent CNPs have been prepared from candle soot by refluxing with HNO₃ and subsequently separated by a single centrifugation. The CNPs can be represented by the empirical formula C₁H_0.677O_0.586N_0.015Na_0.069, and have a size of 20–100 nm, height of 3.0 nm, lifetime of 7.31 ns ± 0.06 ns and quantum yield of ∼1.7%. Further studies demonstrate that: (1) the as-prepared CNPs exhibit excellent stability in biological media and their luminescence intensity does not change with ionic strength or pH in the physiological and pathological range of pH 4.5–8.8; (2) CNPs can act as electron donors and transporters and porphyrin can assemble onto CNPs through electrostatic and π-stacking interactions to form porphyrin-CNPs supramolecular composites; (3) CNPs have strong intrinsic peroxidase-like activity. Based on this intrinsic peroxidase activity, a simple, cheap, and highly selective and sensitive colorimetric and quantitative assay has been developed for the detection of glucose levels. This assay has been used to analyze real samples, such as diluted blood and fruit juice.      

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 facile assay for direct colorimetric visualization of lipopolysaccharides at low nanomolar level

We report a facile assay for the rapid visual detection of lipopolysaccharide (LPS) molecules down to the low nanomolar level by taking advantage of the electrostatic interaction between LPS molecules and cysteamine-modified gold nanoparticles (CSH-Au NPs). The large amount of negatively charged groups on the LPS molecules make LPS highly negatively charged. Thus, when modified with cysteamine, the positively charged gold nanoparticles can aggregate in the presence of trace amounts of LPS. The probe is simple, does not require any advanced instrumentation, and the limit of detection (LOD) was determined to be as low as 3.3 × 10⁻¹⁰ mol/L. To the best of our knowledge, it is the most sensitive synthetic LPS sensor reported so far.      

Shape-controlled synthesis of octahedral α-NaYF4 and its rare earth doped submicrometer particles in acetic acid

Submicrometer sized pure cubic phase, Eu³⁺ doped, and Yb³⁺/Er³⁺ co-doped α-NaYF₄ particles with octahedral morphology have been prepared in acetic acid. The acetate anion plays a critical role in the formation of such symmetric octahedral structures through its selective adsorption on the (111) faces of the products. The size of the as-prepared octahedra can be tuned by varying the amount of sodium acetate added to the acetic acid. A possible formation mechanism for these octahedra has been proposed. The doped α-NaYF₄ octahedral submicrometer particles show down-conversion and up-conversion photoluminescence typical of these materials. This article is published with open access at Springerlink.com     

Gold supported on metal oxides for carbon monoxide oxidation

Au has been loaded (1% wt.) on different commercial oxide supports (CuO, La₂O₃, Y₂O₃, NiO) by three different methods: double impregnation (DIM), liquid-phase reductive deposition (LPRD), and ultrasonication (US). Samples were characterised by N₂ adsorption at −196 °C, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray diffraction, and temperature programmed reduction. CO oxidation was used as a test reaction to compare the catalytic activities. The best results were obtained with Au loaded by DIM on the NiO support, with an activity of 7.2 × 10⁻⁴ mol_CO·g_Au ⁻¹·s⁻¹ at room temperature. This is most likely related to the Au nanoparticle size being the smallest in this catalyst (average 4.8 nm), since it is well known that gold particle size determines the catalytic activity. Other samples, having larger Au particle sizes (in the 2–12 nm range, with average sizes ranging from 4.8 to 6.8 nm), showed lower activities. Nevertheless, all samples prepared by DIM had activities (from 1.1 × 10⁻⁴ to 7.2 × 10⁻⁴ mol_CO·g_Au ⁻¹·s⁻¹, at room temperature) above those reported in the literature for gold on similar oxide supports. Therefore, this method gives better results than the most usual methods of deposition-precipitation or co-precipitation.      

Equilibrium piezoelectric potential distribution in a deformed ZnO nanowire

The equilibrium piezoelectric potential distribution in a deformed ZnO semiconductive nanowire has been systematically investigated in order to reveal its dependence on the donor concentration, applied force, and geometric parameters. In particular, the donor concentration markedly affects the magnitude and distribution of the electric potential. At a donor concentration of N _D>10¹⁸ cm⁻³, the piezopotential is almost entirely screened. Among the other parameters, a variation in the length of the nanowire does not significantly affect the potential distribution.      

Stabilization of the anatase phase of Ti1?xSnxO2 (x < 0.5) nanofibers

We experimentally investigate the stabilization of the anatase phase of Ti_1−x Sn _x O₂ (x < 0.5) nanofibers when synthesized by an electrospinning method. The as-spun nanofibers became nano-grained, polycrystalline nanofibers after calcination and the diameters of the nanofibers depend on Sn content. Stabilization of the anatase phase in Ti-rich compositions and incorporation of Sn ions were confirmed by X-ray diffraction, Raman, X-ray absorption near-edge structure, and photoluminescence (PL) spectroscopies. Results from the PL study also demonstrated the tunable nature of the optical properties, with the emission maximum shifting towards higher wavelength with increasing Sn concentration.      

NiaSi2O5（OH）4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries

Highly crystalline and thermally stable pure multi-walled Ni₃Si₂O₅(OH)₄ nanotubes with a layered structure have been synthesized in water at a relatively low temperature of 200–210 °C using a facile and simple method. The nickel ions between the layers could be reduced in situ to form size-tunable Ni nanocrystals, which endowed these nanotubes with tunable magnetic properties. Additionally, when used as the anode material in a lithium ion battery, the layered structure of the Ni₃Si₂O₅(OH)₄ nanotubes provided favorable transport kinetics for lithium ions and the discharge capacity reached 226.7 mA·h·g⁻¹ after 21 cycles at a rate of 20 mA·g⁻¹. Furthermore, after the nanotubes were calcined (600 °C, 4 h) or reduced (180 °C, 10 h), the corresponding discharge capacities increased to 277.2 mA·h·g⁻¹ and 308.5 mA·h·g⁻¹, respectively.      

Core-shell Au-Ag nanoparticles in dielectric nanocomposites with plasmon-enhanced fluorescence: A new paradigm in antimony glasses

The nano era demands the synthesis of new nanostructured materials, if possible by simplified techniques, with remarkable properties and versatile applications. Here, we demonstrate a new single-step reproducible melt-quench methodology to fabricate core-shell bimetallic (Au⁰-Ag⁰) nanoparticles (28–89 nm) embedded glasses (dielectrics) by the use of a new reducing glass matrix, K₂O-B₂O₃-Sb₂O₃ (KBS) without applying any external reducing agent or multiple processing steps. The surface plasmon resonance (SPR) band of these nanocomposites embedded in KBS glass is tunable in the range 554–681 nm. More remarkably, taking advantage of the selective reduction capability of Sb₂O₃, this single-step methodology is used to fabricate inter-metallic: rare-earth ions co-embedded (Au-Ag:Sm³⁺) dielectric (glass)-based-dnanocomposites and study the effect of enhanced local field on the red upconversion fluorescence of Sm³⁺ ions at 636 nm. The enhancement is found to be about 2 folds. This single-step in-situ selective reduction approach can be used to fabricate a variety of hybrid-nanocomposite devices for laser based applications (see supplementary information). Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

InAs/InP/ZnSe core/shell/shell quantum dots as near-infrared emitters: Bright, narrow-band, non-cadmium containing, and biocompatible

High quality InAs/InP/ZnSe core/shell/shell quantum dots have been grown by a one-pot approach. This engineered quantum dots with unique near-infrared (NIR) fluorescence, possessing outstanding optical properties, and the biocompatibility desired for in vivo applications. The resulting quantum dots have significantly lower intrinsic toxicity compared to NIR emissive dots containing elements such as cadmium, mercury, or lead. Also, these newly developed ultrasmall non-Cd containing and NIR-emitting quantum dots showed significantly improved circulation half-life and minimal reticuloendothelial system (RES) uptake.      

Uniform thickness and colloidal-stable CdS quantum disks with tunable thickness: Synthesis and properties

Uniform thickness and colloidal-stable CdS quantum disks have been reproducibly prepared using cadmium acetate, elemental sulfur, fatty acids and octadecene as the starting materials without any size/shape sorting. The thickness could be varied between 1.2 and 2.2 nm, i.e., 4.5, 5.5, 6.5 and 7.5 monolayers of CdS along the thickness direction. These single crystalline disks with lateral dimensions between 20 and 100 nm adopted the zinc blende crystal structure with 〈100〉 (possibly mixed with 〈111〉) as the thickness direction. The basal planes and side facets were terminated with cadmium carboxylates, which dictated the thicknesses to be half a monolayer more than an integer number. Formation of CdS quantum disks probably occurs through a “nucleation-growth” mechanism, instead of aggregation of pre-formed magic clusters. Completion of a full monolayer along the lateral direction was found to be rather fast if two-dimensional nucleation was initiated on existing disks, which helped formation of atomically flat and thickness-controlled disks. As disk thickness decreased, the crystal lattice was found to dilate gradually, which has not been observed with CdS quantum dots. Compared with CdS quantum dots and rods, the disks displayed weakened quantum confinement and their photoluminescence lifetime (tens of picoseconds) was about two orders of magnitude shorter.      

Synthesis and optical properties of cubic gold nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl₂ ⁻. A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms. The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy. With their hollow and open structures, the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.      

Length-sorted semiconducting carbon nanotubes for high-mobility thin film transistors

We have developed a process for chemical purification of carbon nanotubes for solution-processable thin-film transistors (TFTs) having high mobility. Films of the purified carbon nanotubes fabricated by simple drop coating showed carrier mobilities as high as 164 cm²V⁻¹s⁻¹, normalized transconductances of 0.78 Sm⁻¹, and on/off current ratios of 10⁶. Such high performance requires the preparation of a suspension of micrometer-long and highly purified semiconducting single-walled carbon nanotubes (SWCNTs). Our purification process includes length and electronic-type selective trapping of SWCNTs using recycling gel filtration with a mixture of surfactants. The results provide an important milestone toward printed high-speed and large-area electronics with roll-to-roll and ink-jet device fabrication.      

Magnesium microspheres and nanospheres: Morphology-controlled synthesis and application in Mg/MnO2 batteries

In this paper, we report on the morphology-controlled synthesis of magnesium micro/nanospheres and their electrochemical performance as the anode of primary Mg/MnO₂ batteries. Mg micro/nanoscale materials with controllable shapes have been prepared via a conventional vapor-transport method under an inert atmosphere by adjusting the deposition temperatures. Extensive analysis techniques including SEM, XRD, TEM/HRTEM, and Brunauer-Emmett-Teller (BET) were carried out to characterize the as-obtained samples. The results show that the Mg samples are microspheres or micro/nanospheres with specific surface areas of 0.61–1.92 m²/g. The electrochemical properties of the as-prepared Mg and commercial Mg powders were further studied in terms of their linear sweep voltammograms, impedance spectra, and discharge capability. By comparing the performance of different inhibitors in electrolytes, it was found that NaNO₂ (2.6 mol/L) as an inhibitor in the Mg(NO₃)₂ (2.6 mol/L) electrolyte affords a Mg electrode with high current density and low corrosion rate. In particular, the Mg sample consisting of microspheres with a diameter of 1.5–3.0 μm and nanospheres with a diameter of 50–150 nm exhibited superior electrode properties including negative initial potential (−1.08 V), high current density (163 mA/cm²), low apparent activation energy (5.1 kJ/mol), and high discharge specific capacity (784 mAh/g). The mixture of Mg nanospheres and microspheres is promising for application in primary Mg/MnO₂ batteries because of the sufficient contact with the electrolyte and greatly reduced charge transfer impedance and polarization.      

Electrocondensation and evaporation of attoliter water droplets: Direct visualization using atomic force microscopy

Working with a biased atomic force microscope (AFM) tip in the tapping mode under ambient atmosphere, attoliter (10⁻¹⁸ L) water droplet patterns have been generated on a patterned carbonaceous surface. This is essentially electrocondensation of water leading to charged droplets, as evidenced from electrostatic force microscopy measurements. The droplets are unusual in that they exhibit a highly corrugated surface and evaporate rather slowly, taking several tens of minutes.