Colorimetric detection of mercury ions based on plasmonic nanoparticles.

The development of rapid, specific, cost-effective, and robust tools in monitoring Hg(2+) levels in both environmental and biological samples is of utmost importance due to the severe mercury toxicity to humans. A number of techniques exist, but the colorimetric assay, which is reviewed herein, is shown to be a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, solubility, and stability compared to commonly used organic chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg(2+) is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional molecules. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.

Polydopamine spheres as active templates for convenient synthesis of various nanostructures.

In this work, monodisperse polydopamine (PDA) spheres with tunable diameters have been synthesized through a facile and low cost method using a deionized water and alcohol mixed solvent. The PDA spheres possess surface functional groups (-OH, -NH(2)), exhibiting an extraordinary versatile active nature. It is demonstrated that the PDA spheres could serve as an active template for the convenient synthesis of various nanostructures, e.g., MnO(2) hollow spheres or PDA/Fe(3)O(4) and PDA/Ag core/shell nanostructures. No surface modification or special treatment is required for the synthesis of these nanostructures, which makes the fabrication process simple and very convenient. The novel application of PDA/Fe(3)O(4) spheres as fillers in nanocomposites for high-performance capacitors is demonstrated, indicating a promising practicality. The PDA spheres provide a new general platform not only for the facile assembly of nanostructures but also a green synthetic template for practical applications.

OWL-based nanomasks for preparing graphene ribbons with sub-10 nm gaps.

We report a simple and highly efficient method for creating graphene nanostructures with gaps that can be controlled on the sub-10 nm length scale by utilizing etch masks comprised of electrochemically synthesized multisegmented metal nanowires. This method involves depositing striped nanowires with Au and Ni segments on a graphene-coated substrate, chemically etching the Ni segments, and using a reactive ion etch to remove the graphene not protected by the remaining Au segments. Graphene nanoribbons with gaps as small as 6 nm are fabricated and characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The high level of control afforded by electrochemical synthesis of the nanowires allows us to specify the dimensions of the nanoribbon, as well as the number, location, and size of nanogaps within the nanoribbon. In addition, the generality of this technique is demonstrated by creating silicon nanostructures with nanogaps.

Electrophoretic build-up of alternately multilayered films and micropatterns based on graphene sheets and nanoparticles and their applications in flexible supercapacitors.

Graphene nanosheets and metal nanoparticles (NPs) have been used as nano-building-blocks for assembly into macroscale hybrid structures with promising performance in electrical devices. However, in most graphene and metal NP hybrid structures, the graphene sheets and metal NPs (e.g., AuNPs) do not enable control of the reaction process, orientation of building blocks, and organization at the nanoscale. Here, an electrophoretic layer-by-layer assembly for constructing multilayered reduced graphene oxide (RGO)/AuNP films and lateral micropatterns is presented. This assembly method allows easy control of the nano-architecture of building blocks along the normal direction of the film, including the number and thickness of RGO and AuNP layers, in addition to control of the lateral orientation of the resultant multilayered structures. Conductivity of multilayered RGO/AuNP hybrid nano-architecture shows great improvement caused by a bridging effect of the AuNPs along the out-of-plane direction between the upper and lower RGO layers. The results clearly show the potential of electrophoretic build-up in the fabrication of graphene-based alternately multilayered films and patterns. Finally, flexible supercapacitors based on multilayered RGO/AuNP hybrid films are fabricated, and excellent performance, such as high energy and power densities, are achieved.

Self-organization of a hybrid nanostructure consisting of a nanoneedle and nanodot.

A special materials system that allows the self-organization of a unique hybrid nanonipple structure is developed. The system consists of a nanoneedle with a small nanodot sitting on top. Such hybrid nanonipples provide building blocks to assemble functional devices with significantly improved performance. The application of the system to high-sensitivity gas sensors is also demonstrated.

Nanocomposites of graphene oxide and upconversion rare-earth nanocrystals with superior optical limiting performance.

Upconversion rare-earth nanomaterials (URENs) possess highly efficient near-infrared (NIR), e.g., 980 nm, laser absorption and unique energy upconversion capabilities. On the other hand, graphene and its derivatives, such as graphene oxide (GO), show excellent performance in optical limiting (OL); however, the wavelengths of currently used lasers for OL studies mainly focus on either 532 or 1064 nm. To design new-generation OL materials working at other optical regions, such as the NIR, a novel nanocomposites, GO-URENs, which combines the advantages of both its components, is synthesized by a one-step chemical reaction. Transmission electron microscopy, X-ray diffraction, infrared spectroscopy, and fluorescence studies prove that the α-phase URENs uniformly attach on the GO surface via covalent chemical bonding, which assures highly efficient energy transfer between URENs and GO, and also accounts for the significantly improved OL performance compared to either GO or URENs. The superior OL effect is also observed in the proof-of-concept thin-film product, suggesting immediate applications in making high-performance laser-protecting products and optoelectronic devices.

Synthesis, crystal structure, and optical properties of a three-dimensional quaternary Hg-In-S-Cl chalcohalide: Hg7InS6Cl5.

A crystalline three-dimensional (3D) quaternary chalcohalide, Hg(7)InS(6)Cl(5) (1), has been synthesized through a solid-state reaction under medium temperature. It is the first example in the family of the Hg-IIIA-Q-X (Q = S, Se, Te; X = F, Cl, Br, I) systems. Compound 1 features a 3D network and has an optical band gap of 2.54 eV.

High hardness BaCb-(BxOy/BN) composites with 3D mesh-like fine grain-boundary structure by reactive spark plasma sintering.

Boron carbide B4C powders were subject to reactive spark plasma sintering (also known as field assisted sintering, pulsed current sintering or plasma assisted sintering) under nitrogen atmosphere. For an optimum hexagonal BN (h-BN) content estimated from X-ray diffraction measurements at approximately 0.4 wt%, the as-prepared BaCb-(BxOy/BN) ceramic shows values of Berkovich and Vickers hardness of 56.7 +/- 3.1 GPa and 39.3 +/- 7.6 GPa, respectively. These values are higher than for the vacuum SPS processed B4C pristine sample and the h-BN -mechanically-added samples. XRD and electronic microscopy data suggest that in the samples produced by reactive SPS in N2 atmosphere, and containing an estimated amount of 0.3-1.5% h-BN, the crystallite size of the boron carbide grains is decreasing with the increasing amount of N2, while for the newly formed lamellar h-BN the crystallite size is almost constant (approximately 30-50 nm). BN is located at the grain boundaries between the boron carbide grains and it is wrapped and intercalated by a thin layer of boron oxide. BxOy/BN forms a fine and continuous 3D mesh-like structure that is a possible reason for good mechanical properties.

Bottom-up preparation of porous metal-oxide ultrathin sheets with adjustable composition/phases and their applications.

A facile bottom-up synthesis approach is developed to prepare porous metal-oxide ultrathin sheets, e.g., SnO(2), Fe(2)O(3), and SnO(2)-Fe(2)O(3), with thicknesses of ∼5 nm. Graphene sheets are used as the sacrificing template. Such a process can be extended to the synthesis of multiphased porous metal-oxide thin sheets. These porous thin sheets show interesting applications as gas sensors, effective platforms for matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, and supercapacitors.

Chemical reaction between Ag nanoparticles and TCNQ microparticles in aqueous solution.

The chemical reaction between Ag nanoparticles (Ag NPs) and 7,7',8,8'- tetracycanoquinodimethane (TCNQ) microparticles (MPs) in aqueous solution for the formation of Ag-NP-decorated Ag-TCNQ nanowires is reported. Based on the results obtained by UV-vis spectroscopy and scanning electron microscopy (SEM), it is proposed that the reaction between Ag NPs and TCNQ MPs includes three stages, namely, aggregation of NPs and MPs, diffusion and reaction between NPs and MPs, and formation of Ag-TCNQ nanowires. The as-synthesized semiconducting Ag-TCNQ nanowires show good performance in nonvolatile memory devices with multiple write-read-erase-read (WRER) cycles in air.

Doped amorphous silica nanoparticles as enhancing agents for surface-assisted time-of-flight mass spectrometry.

This article examines the use of doped amorphous silica nanoparticles for surface-assisted laser desorption/ionisation-time of flight-mass spectrometry (SALDI-TOF-MS) of hydrophilic and hydrophobic compounds. A range of particles with surface aliphatic carboxylic, aminophenyl, phenyl or aminopropyl groups have been produced and these have been doped with carbon black, polyaniline or graphite. The effects of surface groups and dopants on the laser desorption/ionisation process were studied. The key factor in effective LDI was the presence of carbon black dopant carrying carboxyphenyl or phenyl residues for positive and negative ion formation. The second key factor was the presence of hydrophilic surface functional groups for hydrophilic amino acid analytes for their detection in positive or negative mode as protonated or de-protonated species respectively whereas hydrophobic surfaces were need for ionisation via cationisation for the hydrophobic analyte squalene. The mechanism for LDI of these particles appears to involve initial adsorption of the analyte onto the surface of the particle, formation of primary ions via adsorption of laser UV irradiation by carboxyphenyl residues attached to the carbon black network which act in an equivalent way to the matrix in matrix-assisted LDI. This is followed by reaction of the primary ions with neighbouring adsorbed analyte molecules. The latter are then released possibly via thermal desorption following proton donation or acceptance from/to via surface residues such carboxylate groups associated with the carbon black within the dopant. Alternatively in the absence of such proton donor/acceptor residues as with hydrophobic particles, the primary ions are released from the particles during desorption and form cation adducts as sodiated and potassiated species in the gas phase above the surface.

Growth of dandelion-shaped CuInSe2 nanostructures by a two-step solvothermal process.

CuInSe(2) (CIS) nanodandelion structures were synthesized by a two-step solvothermal approach. First, InSe nanodandelions were prepared by reacting In(acac)(3) with trioctylphosphine-selenide (TOP-Se) in 1-octadecene (ODE) at 170 °C in the presence of oleic acid. These InSe dandelions were composed of polycrystalline nanosheets with thickness < 10 nm. The size of the InSe dandelions could be tuned within the range of 300 nm-2 µm by adjusting the amount of oleic acid added during the synthesis. The InSe dandelion structures were then reacted with Cu(acac)(2) in the second-step solvothermal process in ODE to form CIS nanodandelions. The band gap of the CIS dandelions was determined from ultraviolet (UV) absorption measurements to be ∼ 1.36 eV, and this value did not show any obvious change upon varying the size of the CIS dandelions. Brunauer-Emmett-Teller (BET) measurements showed that the specific surface area of these CIS dandelion structures was 44.80 m(2) g(-1), which was more than five times higher than that of the CIS quantum dots (e.g. 8.22 m(2) g(-1)) prepared by using reported protocols. A fast photoresponsive behavior was demonstrated in a photoswitching device using the 200 nm CIS dandelions as the active materials, which suggested their possible application in optoelectronic devices.

Controlled CVD growth of Cu-Sb alloy nanostructures.

Sb based alloy nanostructures have attracted much attention due to their many promising applications, e.g. as battery electrodes, thermoelectric materials and magnetic semiconductors. In many cases, these applications require controlled growth of Sb based alloys with desired sizes and shapes to achieve enhanced performance. Here, we report a flexible catalyst-free chemical vapor deposition (CVD) process to prepare Cu-Sb nanostructures with tunable shapes (e.g. nanowires and nanoparticles) by transporting Sb vapor to react with copper foils, which also serve as the substrate. By simply controlling the substrate temperature and distance, various Sb-Cu alloy nanostructures, e.g. Cu(11)Sb(3) nanowires (NWs), Cu(2)Sb nanoparticles (NPs), or pure Sb nanoplates, were obtained. We also found that the growth of Cu(11)Sb(3) NWs in such a catalyst-free CVD process was dependent on the substrate surface roughness. For example, smooth Cu foils could not lead to the growth of Cu(11)Sb(3) nanowires while roughening these smooth Cu foils with rough sand papers could result in the growth of Cu(11)Sb(3) nanowires. The effects of gas flow rate on the size and morphology of the Cu-Sb alloy nanostructures were also investigated. Such a flexible growth strategy could be of practical interest as the growth of some Sb based alloy nanostructures by CVD may not be easy due to the large difference between the condensation temperature of Sb and the other element, e.g. Cu or Co.

High ionic conductivity P(VDF-TrFE)/PEO blended polymer electrolytes for solid electrochromic devices.

Solid polymer electrolytes with excellent ionic conductivity (above 10(-4) S cm(-1)), which result in high optical modulation for solid electrochromic (EC) devices are presented. The combination of a polar host matrix poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and a solid plasticized of a low molecular weight poly(ethylene oxide) (PEO) (M(w)≤ 20,000) blended polymer electrolyte serves to enhance both the dissolution of lithium salt and the ionic transport. Calorimetric measurement shows a reduced crystallization due to a better intermixing of the polymers with small molecular weight PEO. Vibrational spectroscopy identifies the presence of free ions and ion pairs in the electrolytes with PEO of M(w)≤ 8000. The ionic dissolution is improved using PEO as a plasticizer when compared to liquid propylene carbonate, evidently shown in the transference number analysis. Ionic transport follows the Arrhenius equation with a low activation energy (0.16-0.2 eV), leading to high ionic conductivities. Solid electrochromic devices fabricated with the blended P(VDF-TrFE)/PEO electrolytes and polyaniline show good spectroelectrochemical performance in the visible (300-800 nm) and near-infrared (0.9-2.4 µm) regions with a modulation up to 60% and fast switching speed of below 20 seconds. The successful introduction of the solid polymer electrolytes with its best harnessed qualities helps to expedite the application of various electrochemical devices.

Sub-surface, micrometer-scale incisions produced in rodent cortex using tightly-focused femtosecond laser pulses.

BACKGROUND AND OBJECTIVE: Techniques that allow targeted, micrometer-scale disruption in the depths of biological tissue, without affecting overlying structures or causing significant collateral damage, could potentially lead to new surgical procedures. We describe an optical technique to make sub-surface incisions in in vivo rodent brain and characterize the relationship between the cut width and maximum depth of these optical transections as a function of laser energy. MATERIALS AND METHODS: To produce cuts, high intensity, femtosecond laser pulses were tightly focused into and translated within the cortex, through a craniotomy, in anesthetized rodents. Imaging of stained brain slices was used to characterize cut width and maximum cutting depth. RESULTS: Cut width decreased exponentially as a function of depth and increased as the cube root of laser energy, but showed about 50% variation at fixed depth and laser energy. For example, at a laser energy of 13 µJ, cut width decreased from 158 ± 43.1 µm (mean ± standard deviation) to 56 ± 33 µm over depths of approximately 200-800 µm, respectively. Maximal cut depth increased logarithmically with laser energy, with cut depths of up to 1 mm achieved with 13 µJ pulses. We further showcased this technique by selectively cutting sub-surface cortical dendrites in a live, anesthetized transgenic mouse. CONCLUSIONS: Femtosecond laser pulses provide the novel capacity for precise, sub-surface, cellular-scale cuts for surgical applications in optically scattering tissues.

Supercritical Carbon Dioxide-Treated Electrospun Poly(vinylidene fluoride) Nanofibrous Membranes: Morphology, Structures and Properties as an Ionic-Liquid Host.

A reverse-barrier technique is used to enable the treatment of electrospun poly(vinylidene fluoride) nanofibrous membranes with supercritical carbon dioxide. The treatment induces the formation of nanopores and extended-chain ß crystallites of small lateral dimensions in the nanofibers. It also creates interfiber junctions, resulting in a remarkable improvement in mechanical properties of the membranes. The treated membranes are able to retain their shape very well after loading with an ionic liquid (IL). The ionic conductivity of the IL-loaded membrane is very close to that of the neat IL.

Toward electrochromic device using solid electrolyte with polar polymer host.

Polymer electrolyte is an important component in many multilayer devices such as batteries, fuel cells, and electrochromic devices. The effects of polymer electrolyte solidification on the ionic movement and device performance are presented based on near-infrared (IR) (860-2500 nm) electrochromic (EC) devices using the conducting polymer polyaniline. EC devices using electrolyte with polar polymer host of P(VDF-TrFE) show stable and reversible light modulation up to 65% in gel state and 30% in solid state. This is significantly improved when compared to devices with solidified nonpolar polymer host which retains less than 10% light modulation. Electrochemical impedance combined with in situ light modulation measurement identifies various key characteristics exerted by the electrolyte states on device performance. Gel-state devices are affected by the amount of dissociated ions while ionic movement in the electrolyte bulk and through the electrolyte/EC material interface dictates the light modulation in semisolid devices. For solid-state devices, electronic leakage, ionic dissociation, and interaction with electrochrome molecules have been found to limit the operation.

Investigation of the bioactivity and biocompatibility of different glass interfaces with hydroxyapatite, fluorohydroxyapatite and 58S bioactive glass.

The current review investigates the bioactivity of different glass interfaces created on thin glass cover slips as substrates. The interfaces studied are plain glass, functionalized glass using 0.5 M and 5 M of sodium hydroxide (NaOH) for 24 hrs, and glass coated with bioactive 58S Bioglass (58S). A biomimetic method, involving the exposure of the three interfaces to 1.5 times simulated body fluid (SBF) tests the bioactivity of the interfaces via creation of layer of Hydroxyapatite (HA). Fluorinated SBF will precipitate fluorine doped HA (FHA) on a bioactive interface. Higher concentration of 1.5 times of SBF used in this study intended to accelerate the formation of HA and FHA layer over the substrate. HA and FHA is found to be precipitated on the thinly coated 58S. This paper, study also the thin film coatings of three forms of bioceramics - bioactive 58S, HA and FHA. The study, also proposes to draw a relation between the morphology of HA particles with duration of exposure to SBF, the effects of fluorine on the morphology and the cell interaction with bioactive 58S, HA and FHA interfaces using pre-differentiated osteoblastic MC3T3 cells. The analysis of cells in this study is confined to three parameters that include the attachment, proliferation and viability of cells. Tests employed for the analysis of the thin film coating of HA and FHA is restricted to qualitative X-Ray Diffraction and quantitative Field Emission Scanning Electron Microscope. Other mechanical tests such as shear test are not used to test the mechanical properties of this thin layer, due to the fact that the thin film is too thin for such analysis.