Visible‐Light‐Induced Directed Gold Microwires by Self‐Organization of Nanoparticles on Aspergillus Niger

A directional point‐to‐point growth of microwires of gold nanoparticles (AuNPs) self‐organized on Aspergillus niger (A. niger) templates by utilizing positive phototropic fungal response to different spectral ranges of visible light is reported. A. niger serves as a living template for the self‐organization of monosodium glutamate (MSG) capped gold colloids under controlled nutrient trigger and appropriate light, temperature, and humidity conditions. The experimental results show that control of these parameters eliminates the need for any microchannels for the directional growth of microwires. The growth rate of fungal hyphae increases exponentially under light illumination compared to its growth in the dark under similar conditions. White light is found to be most suitable to trigger the directional growth. Gold microwires of about 1 to 2 μm diameter and length exceeding 1 mm are grown within a week with a maximum divergence of 40–50° from the light path regardless of the wavelength of the light irradiation. Phototropic response of fungi has been investigated intensively over the last three decades, but this is the first report on the collective use of microbial tropism and directed biomimetic self‐organization of metallic nanoparticles on living organisms.     

Design of Gold Nanoparticles in Dendritic Cell‐Based Vaccines

The design of effective cancer vaccines must be able to activate dendritic cells (DCs) of the innate immune system in order to induce immunity to pathogens and cancer. DCs patrol the body and once they encounter antigens, they orchestrate a complex mechanism of events and signals that can alert the adaptive immune system to action. However, DC‐based vaccines remain a challenge in part because the source and quality of antigens, the DC targeting molecule, type of adjuvant, and delivery vehicle must be optimized to induce a robust immune response. Gold nanoparticles (AuNPs) have now entered clinical trials as carriers due to their ease of functionalization with antigens, adjuvants, and targeting molecules. This progress report discusses how AuNPs can influence DC activation and maturation, as well as their potential impact on T helper (Th) differentiation. Ultimately, successful AuNP‐based DC vaccines are able to induce phagocytosis, activation/maturation, migration, T cell costimulation, and cytokine secretion, which is named AuNP‐induced DC tuning (AuNP‐DC tuning). Although at its infancy, understanding the processes of AuNP‐DC tuning will give a better understanding of how best to engineer AuNPs and will redefine the next generation of DC‐based vaccines.     

Controlled Formation of TiO2/MoS2 Core–Shell Heterostructures with Enhanced Visible‐Light Photocatalytic Activities

Most recently, much attention has been devoted to photocatalytic materials that may help to solve the global energy crisis and may provide environmental protection. Herein, novel cocatalysts based on few layered MoS₂ and TiO₂ nanomaterials have been designed by growing MoS₂ nanosheets on the surface of TiO₂ nanospheres through a facile hydrothermal method. The method allows the formation of TiO₂/MoS₂ core–shell heterostructures of uniform morphologies and stable structure and provides a good control over shell thickness. The mechanism that forms these heterostructures is discussed in detail. In addition, as cocatalyst, MoS₂ nanosheets can enlarge the light harvesting window to include visible light and improve the photocatalytic ability of TiO₂. Using Rhodamine B as the model, the resultant heterostructure is demonstrated to possess excellent and stable photocatalytic activity in the degradation of organic pollutants under visible light illumination. The TiO₂/MoS₂ heterostructures possess this catalytic activity due to their large surface area and their excellent interface for separating holes and electrons. Therefore, this novel heterostructure nanomaterials possess potential applications in water treatment, degradation of dye pollutants, and environmental cleaning.     

氧化石墨负载金催化剂在以O2为氧源的苯甲醇氧化反应中的催化性能:载体效应

对石墨氧化物经过加热处理和化学处理后担载金溶胶从而制备得到不同的Au/GO催化剂.利用X-射线光电子能谱,热脱附谱和拉曼光谱对催化剂的表面物种和结构进行了表征.结果表明,热处理和化学处理对Au/GO催化剂表面含氧物种的浓度、种类以及载体的晶体结构具有显著影响,进而导致催化剂在以O₂为氧源的液相苯甲醇选择氧化反应中的催化活性呈现明显差异.与载体表面含氧物种的浓度和种类这一因素相比,载体结构的有序程度对于Au/GO催化剂的催化活性起到更为重要的决定作用.     

Metal–Polymer Hybrid Nanoparticles for Correlative High‐Resolution Light and Electron Microscopy

The combination of fluorescence microscopy and electron microscopy promises a deeper insight into the ultrastructural features of cell organelles, e.g., after drug administration. Both methods complement each other and provide, as a correlative approach, a keen insight into the fate of nanoparticles within the cell. Moreover, it represents a promising tool to determine alterations of the cellular environment as a response to particle uptake. However, the availability of suitable correlative markers is mandatory for such correlative approaches. In this contribution, the utilization of poly(ethylene imine) based metal–polymer hybrid particles labeled with small gold nanoparticles and Rhodamine B facilitating the observation of the particles by means of fluorescence as well as by transmission electron microscopy is suggested. Correlative light and electron microscopy is used to study uptake and intracellular fusion processes of endosomal/lysosomal structures.     

Step-addition Method for Enhancing the Yield of Gold Nanoparticles in Block Copolymer Solution

Triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) has been used to synthesize gold nanoparticles from hydrogen tetrachloroaureate (III) hydrate (HAuCl₄·3H₂O) salt in aqueous solution at room temperature. Measurements were performed using the triblock copolymer Pluronic P85 (EO₂₆PO₃₉EO₂₆) at a fixed concentration (1 wt%) mixed with varying HAuCl₄·3H₂O concentration in the range of 0.001 to 0.1 wt%. The surface plasmon resonance (SPR) band in UV-visible absorption spectra confirmed the formation of the gold nanoparticles. The maximum yield of the nanoparticles was found at 0.005 wt% of the salt solution. Small-angle neutron scattering (SANS) does not show any significant change in the scattering profile in these suspensions of the nanoparticles. A similar behavior was also observed in dynamic light scattering (DLS) experiments where autocorrelation function was found to be independent of the salt concentration. This can be understood since a high-block copolymer-to-gold ion ratio (r ～ 22) is required in the reduction reaction to produce gold particles. As a result, a very small fraction of the block copolymers were associated with the gold nanoparticles, and hence lead to a very low yield. Both SANS and DLS basically see the micelles of most of these block copolymers, which are not associated with nanoparticles. Based on this explanation, a step-addition method was used to enhance the yield of gold nanoparticles by manifold, where the gold salt is added in small steps to maintain higher value of r (>22), and therefore continuous formation of nanoparticles.     

High–Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One‐Pot Seeded Growth and Size‐Dependent SERS Property

In this work, uniform, quasi‐spherical gold nanoparticles (Au NPs) with sizes of 31–577 nm are prepared via one‐pot seeded growth with the aid of tris‐base (TB). Distinct from the seeded growth methods available in literature, the present method can be simply implemented by subsequently adding the aqueous dispersion of the 17 nm Au‐NP seeds and the aqueous solution of HAuCl₄ into the boiling aqueous TB solution. It is found that at the optimal pH range, the sizes of the final Au NPs and their concentrations are simply controlled by either the particle number of the Au seed dispersion or the concentration of the HAuCl₄ solution, while the latter enables us to produce large Au NPs at very high concentration. Moreover, as‐prepared Au NPs of various sizes are coated on glass substrates to test their surface‐enhanced Raman scattering (SERS) activities by using 4‐aminothiophenol (4‐ATP) molecules as probes, which exhibit “volcano type” dependence on the Au NP sizes at fixed excitation wavelength. Furthermore, the Au NPs with sizes of ≈97 and 408 nm exhibit the largest SERS enhancement at the excitation wavelength of 633 and 785 nm, respectively.     

Destabilization of Thiolated Gold Clusters for the Growth of Single‐Crystalline Gold Nanoparticles and Their Self‐Assembly for SERS Detection

Thiolate‐protected gold nanoclusters with high chemical stability are exploited extensively for fundamental research and utility in chosen applications. Here for the first time, the controlled destabilization of extraordinarily stable thiolated gold clusters for the growth of single‐crystalline gold nanoparticles (AuNPs) is demonstrated, which was achieved simply via the oxidation of surface‐protecting thiolates into disulfides by hydrogen peroxide under basic condition. By combining with our experimental observations over the entire destabilization and growth process, the new growth mechanism from clusters to AuNPs is revealed by density functional theory (DFT) calculations. It is found that the size of AuNPs decreases with the increase of hydrogen peroxide concentration due to the generation of more nuclei at the higher hydrogen peroxide concentrations. In addition, the preparation of AuNPs is tuned by changing the concentration of hydrogen peroxide, and they are self‐assembled into microspheres via an evaporation‐mediated process, which can induce strong plasmonic coupling between adjacent AuNPs for ultrasensitive surface‐enhanced Raman scattering detection. The present work demonstrates a facile route to functionalize and engineer AuNPs via controlling the reaction conditions and the ratio of precursors, and thus bring new possibilities for using more clusters as precursors to construct novel nano/microstructures for various applications.     

Calcination Effect on the Photoluminescence,Optical, Structural,and Magnetic Properties of Polyvinyl Alcohol Doped ZnFe2O4 Nanoparticles

Abstract

Spinel ferrite based nanoparticle material has been at the forefront of contemporary nanotechnology for use in various industrial and biomedical applications. The preparation and characterization of zinc ferrite nanoparticles (ZFNPs) doped with polyvinyl alcohol (PVA) are reported in this work. The formulated ZFNP/PVAs were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy, photoluminescence (PL) and a vibrating sample magnetometer (VSM). The XRD established the cubic spinel crystal structure of the as-prepared and calcined sample with an increase in the crystallite size after the calcination. The SEM analysis showed a spherical morphology within the range of 10-40?nm after calcination. The bandgap energy was enhanced after calcination. The PL analysis revealed a prominent peak in the UV band, which showed the characteristics of the formulated nanostructure. Transformation to a superparamagnetic nature was observed after calcination. It is noteworthy that after calcination of the formulated ZFNP/PVAs, the structural, optical, bandgap energy, morphology, photoluminescence and the magnetic properties were influenced and enhanced for various applications, chiefly for hyperthermia, magnetic resonance imaging, drug delivery and allied disciplines.     

Determination of the Surface Facets of Gold Nanorods in Wet‐Coated Thin Films with Grazing‐Incidence Wide Angle X‐Ray Scattering

This work studies the surface facets of gold nanorods (AuNRs) in wet‐coated nanoparticle thin films with synchrotron‐light‐based grazing‐incidence wide angle X‐ray scattering (GIWAXS), which provides statistically relevant results on many nanoparticles. Air‐brush spraying deposits the monodisperse AuNRs into sparse monolayers where the long axis of rods is parallel to the substrate surface. It is found that the crystalline facets of individual AuNRs in the sparse monolayer are all in the same orientation, as indicated by narrow azimuthal widths of (200) reflections, over a macroscopic scale comparable to the substrate. This alignment is probably due to the rods' sitting on high‐index surface facets such as (520) and (250). A quantitative analysis of the angles between bulk facets and the surface facets leads to a “nested‐octagon” model for the cross sections of AuNRs: shell octagon with high‐index crystalline facets (520), (5‐20), (2‐50), (‐2‐50), (‐5‐20), (‐520), (‐250), and (250), and core octagon consisting of low‐index crystalline facets (100), (1‐10), (0‐10), (‐1‐10), (‐100), (‐110), (010), and (110).     

Nanoscale Kirkendall Effect and Oxidation Kinetics in Copper Nanocrystals Characterized by Real‐Time,In Situ Optical Spectroscopy

The low‐temperature oxidation of ≈10 nm diameter copper nanocrystals is characterized using in situ UV–vis absorbance spectroscopy and observed to lead to hollow copper oxide shells. The kinetics of the oxidation of solid Cu nanocrystals to hollow Cu₂O nanoparticles is monitored in real‐time via the localized surface plasmon resonance response of the copper. A reaction‐diffusion model for the formation of hollow nanoparticles is fit to the measured time for complete Cu nanocrystal oxidation, and is used to quantify the diffusion coefficient of Cu in Cu₂O and the activation energy of the oxidation process. The diffusivity measured here in single‐crystalline nanoscale systems is 1–5 orders of magnitude greater than in comparable systems in the bulk, and have an Arrhenius dependence on temperature with an activation energy for diffusion of 37.5 kJ mol^?1 for 85 °C ≤ T ≤ 205 °C. These diffusion parameters are measured in some of the smallest metal systems and at the lowest oxidation temperatures yet reported, and are enabled by the unique nanoscale single‐crystalline material and the in situ characterization technique.     

Ultrathin‐Carbon‐Layer‐Protected PtCu Nanoparticles Encapsulated in Carbon Capsules: A Structure Engineering of the Anode Electrocatalyst for Direct Formic Acid Fuel Cells

Structure engineering is an effective strategy to enhance the performance of electrocatalysts for the formic acid oxidation reaction. However, it remains a challenge to prepare a highly active electrocatalyst based on a distinct understanding of its structure‐dependent performance. The design and synthesis of ultrathin‐carbon‐layer‐protected PtCu nanoparticles (NPs) encapsulated in a N‐doped carbon capsule (PtCu@NCC) is reported. This system is fabricated by using Zn‐based metal–organic frameworks as the carbon support source and metal‐containing tannic acid as the protecting shell template. It displays 9.8‐ and 9.6‐fold enhancements in mass activity and specific activity compared to commercial Pt/C. Moreover, a constructed direct formic acid fuel cell using PtCu@NCC as the anodic electrocatalyst delivers a maximum power density of 121 mW cm^?2. Significantly, PtCu@NCC exhibits superior structural stability and catalytic durability in both half‐cell and full‐cell tests. A mechanism study reveals that the enhanced activity is partially attributed to facilitated electro‐oxidation kinetics of formic acid in the unique structure of PtCu@NCC, while the excellent durability stems from the “protecting effect” of the in‐situ‐formed ultrathin carbon layer on the surface of the PtCu NPs. This work opens a new avenue for the development of high‐performance electrocatalysts for fuel‐cell applications by offering essential insights into the structure–performance relationship of the materials.     

Slow and Stopped Light in Active Gain Composite Materials of Metal Nanoparticles: Ultralarge Group Index‐Bandwidth Product Predicted

Chip‐compatible slow light devices with large group index‐bandwidth products and low losses are of great interest in the community of modern photonics. In this work, active gain materials containing metal nanoparticles are proposed as the slow and stopped light materials. Gain‐assisted high field enhancement in metal nanoparticles and the resultant strong dispersion lead to such phenomena. From the Maxwell‐Garnett model, it is revealed that the metal nanocomposite exhibits the infinitely large group index when the gain of the host medium and the filling factor of metal nanoparticles satisfy a critical condition. For the gain of the host above the critical value, one can observe slowing down effect with amplification of light pulses. Significantly large group index‐bandwidth products, which vary from a few to several thousand or even infinity depending on the gain value of the host medium, have been numerically predicted in active silica glasses containing spheroidal metal nanoparticles, as examples. The proposed scheme inherently provides the widely varying operating spectral range by changing the aspect ratio of metal nanoparticles and chip‐compatibility with low cost.     

The Internalization,Distribution, and Ultrastructure Damage of Silica Nanoparticles in Human Hepatic L‐02 Cells

Nowadays, due to the wide use of amorphous silica nanoparticles (SiNPs), their adverse effects on human beings are attracting more attention. Understanding the interaction between SiNPs and cells is a fundamental step for toxicity assessment. Therefore, the current study is aimed at elaborating the internalization process, subcellular distribution, ultrastructure damage, and cytotoxicity of two different sizes of SiNPs (Nano‐Si64 and Nano‐Si46) in L‐02 cells. The results indicate that the smaller‐sized SiNPs, Nano‐Si46, accumulate in cells more efficiently and produce a stronger cytotoxic effect than Nano‐Si64. Both types of nanoparticles can accumulate in L‐02 cells through the active endocytotic pathway and passive diffusion, and distribute within endocytotic vesicles or freely in cytoplasma and organelles. Microvillus fracture, membrane injury, mitochondria damage, degranulation of the rough endoplasmic reticulum, lamellar‐like structure, lysosome destruction, autophagosomes, and autophagy‐lysosomes are found in L‐02 cells. Oxidative damage and direct interaction between SiNPs and subcellular structure are responsible for the toxicity.     

Successive,Seed‐Mediated Growth for the Synthesis of Single‐Crystal Gold Nanospheres with Uniform Diameters Controlled in the Range of 5–150 nm

A simple and robust route is described to the synthesis of single‐crystal Au nanospheres with diameters controlled in the range of 5 nm to 150 nm. The success of this synthesis relies on the use of single‐crystal Au spheres with different diameters as the seeds for successive growth and the use of a slow injection rate for the precursor to enable surface diffusion for the atoms added onto the surface of a seed. The diameters could be precisely controlled by varying the size and/or number of the seeds. The products exhibit excellent uniformity in terms of both size and shape and they are expected to find widespread use in a number of applications, including self‐assembly, fabrication of metallodielectric photonic crystals, plasmonics, and biomedical research.     

Decrease in the Particle Size and Coercivity of Self‐Assembled CoNi Nanoparticles Synthesized Under a Repulsive Magnetic Field

Towards the challenge for synthesis of smaller‐sized heterostructures and hybrid composites for nanomagnets and magnetic fluid applications. Here, a novel method is reported to reduce the particle size of Cobalt–Nickel (CoNi) magnetic nanoparticles by placing them between a static, repulsive magnetic field (N–N/S–S) during synthesis in contrast to the conventional method of applying an attractive (N–S) magnetic field. The obtained smaller sized‐CoNi nanoparticles (≈40 nm) possess a uniform size, an excellent monodispersity, and outstanding magnetic properties. The results clearly demonstrate that the size and morphology change of CoNi nanoparticles have great influence on their magnetic properties. This study provides a footprint to design new heterostructured magnetic nanomaterials under the same‐poled magnetic field for potential applications in magnetic fluids, spintronics, and other related industries.     

The excited state dynamics study of di‐2‐pyridylketone in the A‐band and B‐band absorptions by using resonance Raman spectroscopy,IR and UV–visible spectroscopy

Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S₀→S₄) photo relaxation dynamics have substantial difference from that of B band (S₀→S₁₀) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparing the Basic Phenomena Involved in Three Methods of Pore‐size Characterization: Gas Adsorption,Liquid Intrusion and Thermoporometry

Gas adsorption at 77 K is probably the most widely used method to characterize mesoporous adsorbents via capillary condensation. Mercury intrusion is also commonly used for the characterization of such materials with the possibility to extend the pore width distribution measurement to the macropore range. More recently water intrusion was proposed to study hydrophobic porous solids. Thermoporometry is a further characterization method, now based on the study of the solid/liquid transition. We can consider that all these methods rely on the modification of the phase diagram of a pure substance under the effect of confinement. For each of them, the equations and models derived are based either on classical thermodynamics or on statistical approaches. In most cases, the derivation of the pore width distribution is carried out with the assumption that the porous system is made up of non‐connected cylinders, whereas the actual complexity of the structure is derived from the hysteresis shape. Our aim here is to compare the four approaches above (gas adsorption, mercury intrusion, water intrusion, thermoporometry) on samples giving rise, in their gas adsorption isotherms, to the typical hysteresis loops of the IUPAC classification. Our comparison is in great part carried out after the shape of the hysteresis loops obtained with the various methods and after the information it brings on the mechanism of replacement of a phase by the other within the porous system.     

Influence of light waves on the thermoelectric power under large magnetic field in III‐V,ternary and quaternary materials

We study theoretically the influence of light waves on the thermoelectric power under large magnetic field (TPM) for III‐V, ternary and quaternary materials, whose unperturbed energy‐band structures, are defined by the three‐band model of Kane. The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings in the presence of external photoexcitation. It has been found by taking n‐InAs, n‐InSb, n‐Hg_1‐xCd_xTe and n‐In_1‐xGa_xAs_yP_1‐y lattice matched to InP as examples that the TPM decreases with increase in electron concentration, and increases with increase in intensity and wavelength, respectively in various manners. The strong dependence of the TPM on both light intensity and wavelength reflects the direct signature of light waves that is in direct contrast as compared with the corresponding bulk specimens of the said materials in the absence of external photoexcitation. The rate of change is totally band‐structure dependent and is significantly influenced by the presence of the different energy‐band constants. The well‐known result for the TPM for nondegenerate wide‐gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions and this compatibility is the indirect test of our generalized formalism. Besides, we have also suggested the experimental methods of determining the Einstein relation for the diffusivity:mobility ratio, the Debye screening length and the electronic contribution to the elastic constants for materials having arbitrary dispersion laws.