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Stimuli-responsive materials can sense specific environmental changes and adjust their physical properties in a predictable manner, making them highly desired components for designing novel sensors, intelligent systems, and adaptive structures. Magnetically responsive structures have unique advantages in applications, as external magnetic stimuli can be applied in a contactless manner and cause rapid and reversible responses. In this Perspective, we discuss our recent progress in the design and fabrication of nanostructured materials with various optical responses to externally applied magnetic fields. We demonstrate tuning of the optical properties by taking advantage of the magnetic fields' abilities to induce magnetic dipole--dipole interactions or control the orientation of the colloidal magnetic nanostructures. The design strategies are expected to be extendable to the fabrication of novel responsive materials with new optical effects and many other physical properties. [ABSTRACT FROM AUTHOR]

FTIR spectroscopy has been used to monitor the transport of CO to the Pt cores of Pt@CoO nanoparticles forming CO/Pt species. It was found that external Pt sites are not present on the outer surfaces of the ~10 nm diameter nanostructures and that CO transports to Pt adsorption sites by an activated surface diffusion process through the CoO shells surrounding ~2 nm diameter Pt cores. The CO transport process is not due to gas-phase transport below 300 K. The weakly bound adsorbed CO/CoO species responsible for transport was directly observed at ~2147 cm-1 during transport through the CoO shells. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystals are solution-grown, nanometre-sized, inorganic particles that are stabilized by a layer of surfactants attached to their surface. The inorganic cores possess useful properties that are controlled by their composition, size and shape, and the surfactant coating ensures that these structures are easy to fabricate and process further into more complex structures. This combination of features makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. Chemists are achieving ever more exquisite control over the composition, size, shape, crystal structure and surface properties of nanocrystals, thus setting the stage for fully exploiting the potential of these remarkable materials. [ABSTRACT FROM AUTHOR]

Describes a strategy of combining physical template and capillary forces in assembling monodispersed spherical colloids. Generation and components of hybrid aggregates; Function of colloidal aggregates; Regulation of self-assembled structures.

The article presents information on a study which reveals that surface-mediated shape control and achievement of a hollow morphology can be combined in a one-pot, single-step procedure, which leads to finer tuning of particle morphology. The study has demonstrated that a replacement reaction performed on single crystalline silver nanospheres in an organic solvent produces hollow gold nanocrystals with faceted shape.

Steelmaking contributes 8% to the total CO2 emissions globally, primarily due to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable performance because the dominant gas–solid reduction mechanism is set by the defects and pores inside the mm- to nm-sized oxide particles that change significantly as the reaction progresses. While these governing dynamics are essential to establish continuous flow of iron and its ores through reactors, the direct link between agglomeration and chemistry is still contested due to missing measurements. In this work, we directly measure the connection between chemistry and agglomeration in the smallest iron oxides relevant to magnetite ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we resolve the formation and consumption of wüstite (Fe1-xO)—the step most commonly attributed to whiskering. Using X-ray diffraction, we resolve crystallographic anisotropy in the rate of the initial reaction. Complementary imaging demonstrated how the particles self-assemble, subsequently react, and grow into elongated “whisker” structures. Our insights into how morphologically uniform iron oxide particles react and agglomerate in H2 reduction enable future size-dependent models to effectively describe the multiscale aspects of iron ore reduction. [ABSTRACT FROM AUTHOR]

Examines the self-assembly of spherical colloids into helical chains with well-controlled handedness. Importance of self-assembly in the formation of helical structures; Dewetting of an aqueous dispersion of PS beads from a fluidic cell; Coordination of V-grooves and appropriate building blocks to assemble spherical colloids into multiple copies and of helical chains.

Develops a procedure for generating asymmetric dimers from two types of monodispersed, spherical colloids. Advantages and disadvantages of spherical colloids; Chemical methods developed to synthesize spherical colloids; Use of geometrical confinement and capillary forces to self-assemble two types of spherical colloids.

Describes a solution-phase route for the synthesis of uniform nanowires of crystalline selenium (Se). Properties of solid selenium; Lateral dimensions of amorphous Se; Morphology and structure of Se.

Colloidal assembly into chiral superstructures is usually accomplished with templating or lithographic patterning methods that are only applicable to materials with specific compositions and morphologies over narrow size ranges. Here, chiral superstructures can be rapidly formed by magnetically assembling materials of any chemical compositions at all scales, from molecules to nano- and microstructures. We show that a quadrupole field chirality is generated by permanent magnets caused by consistent field rotation in space. Applying the chiral field to magnetic nanoparticles produces long-range chiral superstructures controlled by field strength at the samples and orientation of the magnets. Transferring the chirality to any achiral molecules is enabled by incorporating guest molecules such as metals, polymers, oxides, semiconductors, dyes, and fluorophores into the magnetic nanostructures. [ABSTRACT FROM AUTHOR]

The article explores the synthesis of titanium dioxide composite nanomaterials and its applications. Topics discussed include metal and metal oxide, nonoxide semiconductor, and carbon titanium oxide composites. Also mentioned are template composites such as anodized aluminum oxide, ordered mesoporous silica and zeolites, and yolk-shell and core-shell.

Colloidal hollow nanocrystals with controlled hollowinterior andshell thickness represent a class of important nanostructured materials,because of their promising applications for nanoreactors, drug delivery,and catalysis. Since the first report in 2004 on the synthesis ofCoS and CoO hollow nanocrystals by sulfidation and oxidation of Conanocrystals, several different kinds of hollow nanocrystals havebeen prepared by a similar approach that involves the nanoscale Kirkendalleffect. In this review, we introduce the application of this well-knownclassical phenomenon in metallurgy in the synthesis of hollow nanocrystals.We start with a brief introduction to the synthesis of hollow nanocrystals,then discuss the concepts and applications of nanoscale Kirkendalleffect for the synthesis of hollow nanocrystals, and finally touchon the extension of the process to the formation of nanotubes. Weconclude with a summary and our personal perspectives on the directionsin which future work on this field might be focused. [ABSTRACT FROM AUTHOR]

We have developed a robust method for the synthesis of silica nanotubes with controlled aspect ratios on a large scale by templating against rod-like nanocrystals. Crystalline nanorods of a nickel–hydrazine complex are first formed in reverse micelles by surfactant capping on side facets, and subsequent silica coating and selective etching give rise to silica nanotubes of high uniformity and yield. The length of the silica nanotubes is tunable in the range 37–340 nm and can reach as long as micrometers. Control of the length is conveniently achieved by tuning the hydrazine/nickel ratio, which affects the growth kinetics of the nanocrystal templates. The inner diameter of the silica nanotubes can be adjusted in the range 10–20 nm by choosing different surfactants. This method is unique in utilizing reverse micelles as discrete nanoscale reactors for the growth of nanocrystals, allowing for precise control of the features of the nanotubes and opening up new opportunities in the synthesis of novel anisotropic nanomaterials, construction of nanodevices, and potential drug delivery applications. [ABSTRACT FROM AUTHOR]

ZnSe nanociystals (NCs), possessing low native luminescence but high biocompatibility, were employed as labeling tags in bioassays. They were able to amplify each target recognition event thousands of times through a cationexchange reaction (CXAmp) that released over 3000 encapsulated Zn2+ from one single NC. The freed cations in turn triggered strong fluorescence from the Zn-responsive dyes. The present study demonstrated that CXAmp with ZnSe delivered superior detection performance in comparison to the conventional labeling methods. The overall fluorescence intensity of CXAinp using 5 nM ZnSe NCs was 30 times higher than that from 5 nM core-shell CdSe/ZnS quantum dots (QDs). The limit of detection (LOD) obtained with ZnSe-based CXPtmp was 10-fold lower than with horseradish peroxidase (HRP) labeling, and the detection sensitivity, represented by the slope of the signalversus-concentration curve, was 20-fold higher. When applied to detect immunoglobulin E (IgE) in a sandwich format, a LOD of 1 ngfmL was achieved. The highly sensitive CXAmp also allowed detection of the total IgE content in dilute human serum, in which the abundant matrix proteins exhibited less interference and more accurate quantification could be performed. Besides high signal amplification efficiency and good biocompatibility, CXAmp with ZnSe could be easily adapted to common laboratory settings and act as a universal labeling system for reliable detection of low-abundance targets. [ABSTRACT FROM AUTHOR]

Here we proved the principle of a multiplexed affinity-based protein complex purification (MAPcP) technique that targets simultaneous extraction of multiple protein complexes with superior purity. Microspheres of various sizes and coupled with different affinity probes extract several protein complexes concurrently and specifically. After the coextraction, flow-field flow fractionation (FlFFF) rapidly washes the microspheres as well as separates them based on their sizes to recover the clean individual complex for downstream analysis. Demonstration of the parallel extraction of two immuno-complexes from the yeast whole cell lysate showed that MAPcP can enhance the sample purity significantly compared to the traditional centrifugation and magnetic pull-down methods used for small scale protein purification. Simultaneous isolation of multiple protein complexes can facilitate the elucidation of the functional relationship among protein complexes and improve our understanding of the biological network. [ABSTRACT FROM AUTHOR]

The electronic structure of cobalt nanocrystals suspended in liquid as a function of size has been investigated using in situ X-ray absorption and emission spectroscopy. A sharp absorption peak associated with the ligand molecules is found that increases in intensity upon reducing the nanocrystal size. X-ray Raman features due to d−d and to charge-transfer excitations of ligand molecules are identified. The study reveals the local symmetry of the surface of -Co phase nanocrystals, which originates from a dynamic interaction between Co nanocrystals and surfactant solvent molecules. [ABSTRACT FROM AUTHOR]

Electrospinning provides a simple approach to fabricating nanofibers and assemblies with controllable hierarchical structures. In this communication, we demonstrate that electrospinning can be combined with calcination to further maneuver the morphology and phase structure of nanofibers. More specifically, single-crystal V2O5 nanorods could be grown on rutile nanofibers by carefully calcining composite nanofibers consisting of amorphous V2O5, amorphous TiO2, and poly(vinylpyrrolidone). The size of the resulting V2O5 nanorods could be conveniently controlled by varying the composition of the nanofibers and/or the calcination temperature. In addition to the nanorod-on-nanofiber hierarchical structure, we believe this approach can also be extended to fabricate other more complex architectures. [ABSTRACT FROM AUTHOR]

The article presents coupling morphological and magnetic anisotropy for assembling tetragonal colloidal crystals. Topics discussed include Morphological and magnetic anisotropy can be combined in colloidal assembly to create unconventional secondary structures; and show that magnetite nanorods interact along a critical angle, depending on their aspect ratios and assemble into body-centered tetragonal colloidal crystals.

Clusters of densely packed hydrophobic superparamagnetic γ-Fe2O3nanocrystals have been developed as a powerful adsorbent for enrichment of peptides and proteins, with advantages such as high enrichment efficiency, fast processing, easy magnetic separation, and direct mass analysis. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS) rubber can be thermally decomposed in air to produce silica vapor species which can deposit on porous anodic aluminum oxide (AAO) templates to produce silica nanotubes with a smooth surface and highly controllable thickness. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction of CO2 holds great promises for addressing both the environmental and energy issues that are facing the modern society. The major challenge of CO2 photoreduction into fuels such as methane or methanol is the low yield and poor selectivity. Here, we report an effective strategy to enhance the reduction potential of photoexcited electrons by fluorination of mesoporous single crystals of reduced TiO2-x. Density functional theory calculations and photoelectricity tests indicate that the Ti3+ impurity level is upswept by fluorination, owing to the built-in electric field constructed by the substitutional F that replaces surface oxygen vacancies, which leads to the enhanced reduction potential of photoexcited electrons. As a result, the fluorination of the reduced TiO2-x dramatically increases the CH4 production yield by 13 times from 0.125 to 1.63 µmol/g·h under solar light illumination with the CH4 selectivity being improved from 25.7% to 85.8%. Our finding provides a metal-free strategy for the selective CH4 generation from CO2 photoreduction. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide is a highly toxic molecule to human health, but high-performance detection of it remains a challenge. Herein, we report an ultrasensitive photoelectrochemical (PEC) sensor for H2S by modifying indium tin oxide (ITO) electrodes with Cd2+-doped amorphous TiO2 hollow spheres, which are prepared by templating against colloidal silica particles followed by a cadmium-sodium cation exchange reaction. The amorphous TiO2 hollow spheres act as both the probing cation carrier and the photoelectric beacon. Upon exposure to sulfide ions, the photocurrent of the functionalized photoanode proportionately decreases in response to the formation of CdS nanoparticles. The decreased photocurrent could be attributed to the mismatching bandgap between the amorphous TiO2 and CdS nanoparticles: the photoexcited electrons and holes from amorphous TiO2 are transferred to the conduction band and valence band of CdS, respectively, and then recombined. The decrease in photocurrent is linear with the concentration of sulfide ions in the range from 1 to 10 000 pmol L-1 with a detection limit of 0.36 pmol L-1. Enabled by a unique sensitization mechanism, this PEC sensor features excellent performance in a wide linear range, high selectivity and sensitivity, high stability, and low fabrication cost. [ABSTRACT FROM AUTHOR]

A novel ratiometric surface-enhanced Raman scattering (SERS) nanosensor has been developed to probe the activity of endonuclease under in vitro and in living cells conditions. The optimized alloyed Au/Ag nanoparticles (NPs) were synthesized as the SERS substrate, which combined the superior properties of both pure Au and pure Ag nanoparticles: they exhibit excellent plasmonic property with high chemical stability and low cytotoxicity. They were then employed for quantitative detection of endonuclease through functionalization with single-stranded DNA (ssDNA) carrying 3-[4- (phenylethynyl)benzylthio]propanoic acid (PEB) as endonucleaseresponsive SERS signaling molecule and 4-thiophenylacetylene (TPA) as the internal standard SERS signaling molecule. In the presence of endonuclease, the ssDNA was cleaved, releasing PEB molecules from the particle surface and decreasing the SERS signal at 2215 cm-1 from PEB. Since the SERS signal at 1983 cm-1 from alkynyl TPA remained the same, quantitative detection of endonuclease was achieved, based on the ratiometric peak intensity of I1983/I2215, with a detection limit as low as 0.056 unit/mL. A highly biocompatible and antijamming ratiometric SERS sensor was established by combining the alloyed Au/AgNPs with two unique alkynes molecules with Raman signals in the cellular silent region. The ratiometric sensor was successfully employed to detect intracellular endonuclease activity as well as endonuclease in living cells for the first time. [ABSTRACT FROM AUTHOR]

We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent Cs4PbX6 (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX3 NCs. During the transformation, Cs4PbX6 NCs dispersed in a nonpolar solvent are converted into CsPbX3 NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of Cs4PbX6 NCs, and produces monodisperse and air-stable CsPbX3 NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as Cs4PbX6 NCs are converted into CsPbX3 NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX3 NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX3 NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals. [ABSTRACT FROM AUTHOR]

When nanocrystals are made to undergo chemical transformations, there are often accompanying large mechanical deformations and changes to overall particle morphology. These effects can constrain development of multistep synthetic methods through loss of well-defined particle morphology and functionality. Here, we demonstrate a surface protection strategy for solution phase chemical conversion of colloidal nanostructures that allows for preservation of overall particle morphology despite large volume changes. Specifically, via stabilization with strong coordinating capping ligands, we demonstrate the effectiveness of this method by transforming β-FeOOH nanorods into magnetic Fe3O4 nanorods, which are known to be difficult to produce directly. The surface-protected conversion strategy is believed to represent a general self-templating method for nanocrystal synthesis, as confirmed by applying it to the chemical conversion of nanostructures of other morphologies (spheres, rods, cubes, and plates) and compositions (hydroxides, oxides, and metal organic frameworks). [ABSTRACT FROM AUTHOR]

Developing efficient photoreversible color switching systems for constructing rewritable paper is of significant practical interest owing to the potential environmental benefits including forest conservation, pollution reduction, and resource sustainability. Here we report that the color change associated with the redox chemistry of nanoparticles of Prussian blue and its analogues could be integrated with the photocatalytic activity of TiO2 nanoparticles to construct a class of new photoreversible color switching systems, which can be conveniently utilized for fabricating ink-free, light printable rewritable paper with various working colors. The current system also addresses the phase separation issue of the previous organic dye-based color switching system so that it can be conveniently applied to the surface of conventional paper to produce an ink-free light printable rewritable paper that has the same feel and appearance as the conventional paper. With its additional advantages such as excellent scalability and outstanding rewriting performance (reversibility >80 times, legible time >5 days, and resolution >5 μm), this novel system can serve as an eco-friendly alternative to regular paper in meeting the increasing global needs for environment protection and resource sustainability. [ABSTRACT FROM AUTHOR]

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and reactors, optical properties and applications, magnetic properties, energy storage, catalysis, biomedical applications, environmental remediation, and sensors. Finally, we provide a perspective on future development in the research relevant to hollow micro-/nanostructures. [ABSTRACT FROM AUTHOR]

Structural defects have been proven to determine many of the materials' properties. Here, we demonstrate a unique approach to the creation of Ag nanowires with high-density defects through controllable nanoparticles coalescence in one-dimensional pores of mesoporous silica. The density of defects can be easily adjusted by tuning the annealing temperature during synthetic process. The high-density defects promote the adsorption and activation of more reactants on the surface of Ag nanowires during catalytic reactions. As a result, the as-prepared Ag nanowires exhibit enhanced activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and turnover frequency (TOF). We show further that the silane conversion rate can be enhanced by maximizing the defect density and thus the number of active sites on the Ag nanowires, reaching a remarkable TOF of 8288 h-1, which represents the highest TOF that has been achieved by far on Ag catalysts. This work not only proves the important role of structural defects in catalysis but also provides a new and general strategy for constructing high-density defects in metal catalysts. [ABSTRACT FROM AUTHOR]

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ~1.3 x 107 on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications. [ABSTRACT FROM AUTHOR]

Monodispersed silica spheres with solid core and fibrous shell were successfully synthesized using a biphase reaction. Both the thickness and the pore size of the fibrous shell could be finely tuned by changing the stirring rate during synthesis. When stirring was adjusted from 0 to 800 rpm, the thickness of the shell could be tuned from 13 to 67 nm and the pore size from 5 to 16 nm. By continuously adjusting the stirring rate, fibrous shells with hierarchical pore structure ranged from 10 to 28 nm and thickness up to 200 nm could be obtained in one pot. We demonstrate that fibrous shells with controllable thickness and pore size could be coated on silica cores with diameters from 0.5 to 3 µm while maintaining the monodispersity of the particles. As a result of the unique fibrous structure, the BET surface area could reach ~233 m² g-1 even though the shell thickness was less than 150 nm. The core-shell particles were modified with C18, packed, and then used in high-performance liquid chromatography (HPLC) separation, showing separation performance as high as 2.25 x 105 plates m-1 for naphthalene and back pressure as low as 5.8 MPa. These silica microspheres with fibrous shells are expected to have great potential for practical applications in HPLC. [ABSTRACT FROM AUTHOR]

We demonstrate that anatase TiO2 nanocrystals composed of a nanocrystal core and nanorod antennas can be produced via a nonaqueous colloidal seed-mediated growth method. Anatase TiO2 nanocrystals with defined morphologies were first prepared as seeds, and then secondary anatase TiO2 nanorods were grown on the defined facets of the seeds under appropriate conditions. Systematic studies on the growth mechanism reveal that the formation of core--antenna nanocrystals involves an epitaxial growth process with specific orientational preference governed by both thermodynamic and kinetic factors. By manipulating the reaction conditions including the precursor amount and introduction rate, the epitaxial growth behavior can be well controlled. By further varying the morphology of seed nanocrystals, we have also been able to produce core-antenna anatase TiO2 nanocrystals with complex spatial configurations in a highly predictable manner. The high structural configurability and predictability offered by this seed-mediated growth method may provide great opportunities in enhancing the performance of TiO2-based nanostructures in many energy-related applications. As a demonstration, we show by simply manipulating the core--antenna structures that the photocatalytic activity of the anatase nanocrystals can be improved from the relatively less active seed nanocrystals or pure nanorods to the extent that exceeds the activity of the commercial P2S titania. [ABSTRACT FROM AUTHOR]

Examines the synthesis of single-crystalline nanowires of Ag[sub 2]Se by templating against nanowires of trigonal Se. Template-directed reaction through which the morphology and single crystallinity of the template were both retained with high fidelity; Extension of the synthetic strategy to other systems by keeping in mind that the reconstruction of the parent crystal lattice is kept minimal.

The production of hydrogen from water with semiconductor photocatalysts can be promoted by adding small amounts of metals to their surfaces. The resulting enhancement in photocatalytic activity is commonly attributed to a fast transfer of the excited electrons generated by photon absorption from the semiconductor to the metal, a step that prevents deexcitation back to the ground electronic state. Here we provide experimental evidence that suggests an alternative pathway that does not involve electron transfer to the metal but requires it to act as a catalyst for the recombination of the hydrogen atoms made via the reduction of protons on the surface of the semiconductor instead. [ABSTRACT FROM AUTHOR]

We report that fully alloyed Ag/Au nanospheres with high compositional homogeneity ensured by annealing at elevated temperatures show large extinction cross sections, extremely narrow bandwidths, and remarkable stability in harsh chemical environments. Nanostructures of Ag are known to have much stronger surface plasmon resonance than Au, but their applications in many areas have been very limited by their poor chemical stability against nonideal chemical environments. Here we address this issue by producing fully alloyed Ag/Au nanospheres through a surface-protected annealing process. A critical temperature has been found to be around 930 °C, below which the resulting alloy nanospheres, although significantly more stable than pure silver nanoparticles, can still gradually decay upon extended exposure to a harsh etchant. Nanospheres annealed above the critical temperature show a homogeneous distribution of Ag and Au, minimal crystallographic defects, and the absence of structural and compositional interfaces, which account for the extremely narrow bandwidths of the surface plasmon resonance and may enable many plasmonic applications with high performance and long lifetime, especially for those involving corrosive species. [ABSTRACT FROM AUTHOR]

By using gold nanorods as an example, we report the dynamic and reversible tuning of the plasmonic property of anisotropically shaped colloidal metal nanostructures by controlling their orientation using external magnetic fields. The magnetic orientational control enables instant and selective excitation of the plasmon modes of AuNRs through the manipulation of the field direction relative to the directions of incidence and polarization of light. [ABSTRACT FROM AUTHOR]

We report a general method for the synthesis of noble metal nanorods, including Au, Ag, Pt, and Pd, based on their seeded growth in silica nanotube templates. The controlled growth of the metals occurs exclusively on the seeds inside the silica nanotubes, which act as hard templates to confine the one-dimensional growth of the metal nanorods and define their aspect ratios. This method affords large quantities of noble metal nanorods with well-controlled aspect ratios and high yield, which may find wide use in the fields of nanophotonics, catalysis, sensing, imaging, and biomedicine. [ABSTRACT FROM AUTHOR]

Interparticle magnetic dipole force has been found to drive the formation of dynamic superparamagnetic colloidal particle chains that can lead to the creation of photonic nanostructures with rapidly and reversibly tunable structural colors in the visible and near-infrared spectrum. Although most studies on magnetic assembly utilize simple permanent magnets or electromagnets, magnetic fields, in principle, can be more complex, allowing the localized modulation of assembly and subsequent creation of complex superstructures. To explore the potential applications of a magnetically tunable photonic system, we study the assembly of magnetic colloidal particles in the complex magnetic field produced by a nonideal linear Halbach array. We demonstrate that a horizontal magnetic field sandwiched between two vertical fields would allow one to change the orientation of the particle chains, producing a high contrast in color patterns. A phase transition of Fe3O4@SiO2particles from linear particle chains to three-dimensional crystals is found to be determined by the interplay of the magnetic dipole force and packing force, as well as the strong electrostatic force. While a color pattern with tunable structures and diffractions can be instantly created when the particles are assembled in the form of linear chains in the regions with vertical fields, the large field gradient in the horizontal orientation may destabilize the chain structures and produces a pattern of 3D crystals that compliments that of initial chain assemblies. Our study not only demonstrates the great potential of magnetically responsive photonic structures in the visual graphic applications such as signage and security documents but also points out the potential challenge in pattern stability when the particle assemblies are subjected to complex magnetic fields that often involve large field gradients. [ABSTRACT FROM AUTHOR]

Silver nanoplates with an extremely high aspect ratio (up to over 400) and a widely tunable surface plasmon resonance (SPR) band have been successfully synthesized by combining the concepts of selective ligand adhesion and seeded growth. Citrate ligands are used as the sole surfactant to effectively block overgrowth on the basal {111} facets and only allow growth in the lateral direction. By slowing down the reaction rate using Ag−citrate complex as precursor, the thin nature of Ag nanoplates is maintained with the edge length grown up to 4 μm, which ensures the high aspect ratio and the widely tunable SPR band. We also observe a size distribution focusing effect that helps to produce uniform nanoplates as well as narrow SPR bands over a wide range, which is important in many practical applications. [ABSTRACT FROM AUTHOR]

The high carrier mobility of graphene makes it an attractive candidate for future electronic device applications.1In SiO2/Si-supported graphene devices, the mobility typically varies from 2000 to ∼20000 cm2V−1s−1.2By removing SiO2,3,4much higher mobility (2 × 105cm2V−1s−1in the latter) has been obtained, suggesting the importance of the Coulomb scattering in graphene transport. Although such elaborate device fabrication is clearly effective, the mobility of finished devices is fixed thereafter and can vary from device to device. In this work, we first demonstrate a significant enhancement in carrier mobility in SiO2-supported graphene decorated with a layer of ligand-bound nanoparticles (NPs) such as iron oxide, titanium dioxide, or cadmium selenide acting as a charge reservoir. By transferring charges between graphene and the NP reservoir through the molecules, we show a remarkable reversible tunability in mobility (4000−19000 cm2V−1s−1) in the samedevice, which unambiguously proves that the charged impurity scattering is the prevailing mechanism for graphene mobility. In addition, the charge neutral point or the Dirac point can also be independently tuned over a wide gate voltage range. The reversible tuning is useful for fabricating large-area graphene devices such as nonvolatile memory with enhanced sensitivity. [ABSTRACT FROM AUTHOR]

A one-pot solution process has been devised to synthesize colloidal Bi2Te3-Te heterogeneous nanostructures (HNs) that comprise Bi2Te3 nanoplates and Te nanorods. By controlling the reaction kinetics, the reaction of TeO32- and Bi2Te3 in the presence of hydrazine first produces uniform Te nanorods and then grows Bi2Te3 nanoplates on the tips and surfaces of these Te nanorods, forming various shapes including "nails", "barbells", "syringes", and "accordions". The specific topological arrangement realized arises from the peculiar anisotropic reactivity of the first formed Te nanorods, whose tips are subsequently exploited to seed the heterogeneous nucleation of Bi2Te3 as enabled by the similar crystal structure and the small lattice mismatch between Te and Bi2Te3. Three important processes, heterogeneous nucleation of Bi2Te3 on the tips and/or surface of Te nanorods, homogeneous nucleation of Bi2Te3, and the direct reaction of a Bi precursor and Te nanorods to form hollow structures via the Kirkendall Effect, occur under various conditions. The manipulation of these processes provides a robust means for the fine shape control of Bi2Te3-Te HNs. It is envisioned that the tailored synthesis of Bi2Te3-Te HNs may promise unique opportunities for producing thermoelectric materials with greatly enhanced performance. [ABSTRACT FROM AUTHOR]

We report the rapid formation of photonic crystal structures by assembly of uniform nonmagnetic colloidal particles in ferrofluids using external magnetic fields. Magnetic manipulation of nonmagnetic particles with size down to a few hundred nanometers, suitable building blocks for producing photonic crystals with band gaps located in the visible regime, has been difficult due to their weak magnetic dipole moment. Increasing the dipole moment of magnetic holes has been limited by the instability of ferrofluids toward aggregation at high concentration or under strong magnetic field. By taking advantage of the superior stability of highly surface-charged magnetite nanocrystal-based ferrofluids, in this paper we have been able to successfully assemble 185 nm nonmagnetic polymer beads into photonic crystal structures, from 1D chains to 3D assemblies as determined by the interplay of magnetic dipole force and packing force. In a strong magnetic field with large field gradient, 3D photonic crystals with high reflectance (83%) in the visible range can be rapidly produced within several minutes, making this general strategy promising for fast creation of large-area photonic crystals using nonmagnetic particles as building blocks. [ABSTRACT FROM AUTHOR]

Protein phosphorylation plays a key role in most cellular processes. Studying phosphopeptides in complex biological samples has been a great challenge due to their low abundance as well as the coexistence of excessive amounts of salts or surfactants. In this work we demonstrate a general approach for selective separation of phosphopeptides using a class of novel mesoporous nanostructured materials. TiO2 nanocrystals are first self-assembled into submicrometer clusters containing relatively uniform mesoscale pores and then stabilized by coating with a thin layer of silica. Calcination of the materials at high temperatures connects the neighboring nanocrystals together and enhances the mechanical stability of the clusters and at the same time removes the organic surfactants and makes the TiO2 surface fully accessible to phosphopeptides. By coating the nanocrystal clusters with a layer of silica before calcination and removing it afterward through chemical etching, we have been able to make the cluster surface hydrophilic and negatively charged, thus enhancing the water dispersibility of the clusters and eventually their accessibility to phosphopeptides. The high selectivity and capacity of these mesoporous TiO2 clusters have been demonstrated by effectively enriching phosphopeptides from digests of phosphoprotein (α- or β-casein), protein mixtures of β-casein and bovine serum albumin, milk, and human serum samples. We also demonstrate that the self-assembly process brings the flexibility of incorporation of multiple components, such as superparamagnetic nanocrystals, to further facilitate the peptide separation. [ABSTRACT FROM AUTHOR]

Copper(l) sulfide (Cu2S) nanodisks with controllable size and aspect ratio have been synthesized by using a one-pot colloidal process, in which no pre-prepared organometallic precursors are required. The reaction involves the injection of dodecanethiol into a hot solution containing copper salt, surfactants, and a high boiling-point organic solvent. Copper thiolate forms at the beginning at the reaction which effectively acts as a precursor whose decomposition leads to further nucleation and growth of Cu2S nanocrystals. The nanocrystals begin as small nanodots in the early stages ot the reaction, gradually turning into nanodisks with aspect ratios (average disk diameter divided by thickness) up to 2.0, while the band gap ot the nanocrystals decreases accordingly. As the growth ot nanocrystals follows the monomer addition mechanism, the diameter, thickness, aspect ratio, and optical property of the Cu2S nanodisks can be tuned systematically by changing the reaction time, the amount ot surfactants, and the concentration of the precursors. This synthesis provides a simple and highly reproducible method for the preparation at Cu2S nanocrystals that may find potential applications in the fabrication of photovoltaic devices. [ABSTRACT FROM AUTHOR]

Small RNA molecules are effective regulators of gene expression, and the expression signature of one subgroup of small RNA, the microRNA (miRNA), has been linked to disease development and progression. Therefore, detection of small RNA in biological samples will greatly improve the understanding of their functions and render effective tools to researchers for cellular process control and disease prevention. To solve the challenges in detecting the low-abundance and short strand-length of small RNA molecules, we designed a ligation-assisted binding assay and applied the cation exchange-based fluorescence amplification (CXFluoAmp) method developed in our group for detection. Nonfluorescent, ionic nanocrystals (NCs) of CdSe were conjugated to detection probes and immobilized onto the array surface via ligation with the target small RNA, miR21, which bound to the capture probe complimentarily. Each binding event induced by one target miR21 molecule was then amplified by the release of thousands of Cd2+ from one NC. The free Cd2+ immediately turned on the fluorescence of thousands of fluorogenic Rhod-5N molecules. With such a powerful signal amplification strategy, our assay achieved a limit of detection (LOD) of 35 fM and signals were detectible with analyte concentrations spanning over 7 orders of magnitude. We also identified the differential expression of miR21 in total RNA extracts from healthy breast tissue and diseased cells. Furthermore, our detection scheme demonstrated good specificity in small RNA detection, because significant signal intensity could be observed from small RNAs with one or two nucleotides difference in sequences. Thus, our assay has great application potential for disease diagnosis relying on miRNA biomarkers, or in small RNA expression profiling for new target discovery and functional study. [ABSTRACT FROM AUTHOR]

Magnetochromatic microspheres have been fabricated through instant assembly of superparamagnetic (SPM) colloidal particles inside emulsion droplets of UV curable resin followed by an immediate UV curing process to polymerize the droplets and fix the ordered structures. When dispersed in the liquid droplets, superparamagnetic Fe3O4@SiO2 core/shell particles self-organize under the balanced interaction of repulsive and attractive forces to form one-dimensional chains, each of which contains periodically arranged particles diffracting visible light and displaying field-tunable colors. UV initiated polymerization of the oligomers of the resin fixes the periodic structures inside the droplet microspheres and retains the diffraction property. Because the superparamagnetic chains tend to align themselves along the field direction, it is very convenient to control the orientation of such photonic microspheres and, accordingly, their diffractive colors, by changing the orientation of the crystal lattice relative to the incident light using magnetic fields. The excellent stability together with the capability of fast on/off switching of the diffraction by magnetic fields makes the system suitable for applications such as color display, rewritable signage, and sensors. As a simple demonstration, we have fabricated a display unit that has on/off bistable states by embedding the magnetochromatic microspheres in a matrix that can thermally switch between solid and liquid phases. [ABSTRACT FROM AUTHOR]

Many creatures in nature, such as butterflies and peacocks, display unique brilliant colours, known as ‘structural colours’, which result from the interaction of light with periodic nanostructures on their surfaces. Mimicking such nanostructures found in nature, however, requires state-of-the-art nanofabrication techniques that are slow, expensive and not scalable. Herein, we demonstrate high-resolution patterning of multiple structural colours within seconds, based on successive tuning and fixing of colour using a single material along with a maskless lithography system. We have invented a material called ‘M-Ink’, the colour of which is tunable by magnetically changing the periodicity of the nanostructure and fixable by photochemically immobilizing those structures in a polymer network. We also demonstrate a flexible photonic crystal for the realization of structural colour printing. The simple, controllable and scalable structural colour printing scheme presented may have a significant impact on colour production for general consumer goods. [ABSTRACT FROM AUTHOR]

We describe a “surface-protected etching” strategy that allows convenient conversion of sol−gel derived silica into porous structures. Poly(vinyl pyrrolidone) is used to protect the near surface layer, and NaOH is used to selectively etch the interior of the silica spheres. Etching initially yields porous structures and eventually removes the core to leave behind hollow silica spheres with porous shells. This strategy is useful for constructing core−shell systems where active nanomaterials are embedded in silica shell for enhanced stability against aggregation. We experimentally demonstrate use of the surface-protected etching approach to create openings on silica shells; these openings allow dissolved chemical species to reach embedded catalytic particles to be chemically transformed while the porous shells continue to act as effective barriers against aggregation and loss of activity of the core particles. We also show that, by controlling the extent of etching, it is possible to control the permeation rate of the chemical species through the shells. [ABSTRACT FROM AUTHOR]

Superparamagnetic Fe3O4colloids with highly charged surfaces have been assembled into ordered structures in water in response to external magnetic fields. The colloids form chainlike structures with regular interparticle spacings of a few hundred nanometers along the direction of the external field so that the system strongly diffracts visible light. The balance between attractive (in this case, magnetic) and repulsive (electrostatic) forces dictates interparticle spacing and therefore optical properties. By changing the relative strength of these two forces, one can tune the peak diffraction wavelength over the entire visible spectrum. We were able to optimize the diffraction intensity and the tuning range through studying their dependence on variables such as the size distribution and concentration of the Fe3O4colloids or ionic strength of the solutions. The fast, reversible response and the feasibility for miniaturization impart these photonic materials great potential in applications such as optoelectronic devices, sensors, and color displays. [ABSTRACT FROM AUTHOR]

Hydrophobic inorganic nanocrystals have been transferred from organic solvent to aqueous solution through a robust and general ligand exchange procedure. Polyelectrolytes such as poly(acrylic acid) and poly(allylamine) are used to replace the original hydrophobic ligands on the surface of nanocrystals at an elevated temperature in a glycol solvent and eventually render the nanocrystals highly water soluble. The physical properties of the nanocrystals, such as superparamagnetism, photocatalytic activity, and photoluminescence, are maintained or improved after ligand exchange. [ABSTRACT FROM AUTHOR]

A self-templated approach has been developed for the synthesis of TiO2microcapsules with tunable size and wall thickness by heating sol−gel derived TiO2microspheres with poly(acrylic acid) (PAA) in a diethylene glycol (DEG) solution. PAA plays a crucial role in the formation of microcapsules by crosslinking the surface TiO2nanoparticles and preventing them from dissolution by DEG. Hollow microcapsules form when DEG molecules penetrate the outer layer and remove the core materials by forming soluble titanium glycolate. [ABSTRACT FROM AUTHOR]