Polymer Composites with Plasmonic Metal Nanoparticles

Summary: A two-phase method has been adapted for the preparation of polymer composites consisting of regioregular poly(3-octylthiophene-2,5-diyl) and Au or Ag nanoparticles. This work compares optical and morphological properties of nanocomposites formed by mixing metal organosols and polymer solution (type I composites) with nanocomposites formed by in-situ reduction in polymer solutions (type II composites). Both types contained very small metal nanoparticles (1–10 nm). Interestingly, more than ten-fold enhancement of Raman scattering of the polymer by the electromagnetic (EM) mechanism of SERS (surface-enhanced Raman scattering) resulted from the coupling of the polymer with plasmonic Au nanoparticles into a nanocomposite system.     

Metal Nano Networks by Potential-Controlled In Situ Assembling of Gold/Silver Nanoparticles

Non-spherical Au/Ag nanoparticles can be generated by chemical reduction of silver ions in the presence of preformed gold nanoparticles. The process of particle formation can be controlled by concentrations of ligands and reducing agent. The formation of ellipsoidal, nanorod- and peanut-shaped nanoparticles as well as of more complex fractal nanoassemblies can be explained by changes in particle surface state, electrochemical potential formation and particle-internal self-polarization effects. It is possible to create highly fractal nanoassemblies with sizes between the mid-nanometer and the lower micrometer range. The assemblies are marked by high optical absorption and complex nano-networks of very high surface-to-volume ratios and a granular base structure.     

纳米银形状控制合成与聚合物纳米银复合材料

纳米银(Ag NPs)由于其独特的物理、化学和生物学特性备受研究人员的关注.纳米银应用性能除了受到粒子尺寸、分布、纯度等因素影响,还与纳米银的形状密切相关.纳米银的形状对纳米银的抗菌性能、光学性能以及聚合物纳米银复合材料的综合性能都会产生重要影响.纳米银的形状控制合成可以进一步发挥聚合物纳米银复合材料的性能潜力.因此,不断发展纳米银新的合成方法,研究纳米银形状控制的机理就显得尤为重要.本文综述了纳米银合成方法和不同形状纳米银的最新研究进展,合成方法重点介绍了辐射法、激光烧蚀法、电化学法、光化学法和生物合成法,评述了这些方法的优缺点;同时从模板法、动力学、热力学以及氧化刻蚀4个方面介绍了纳米银形状控制的机理.介绍了聚合物纳米银复合材料的研究进展.     

Overview of Synthetic Methods to Prepare Plasmonic Transition-Metal Nitride Nanoparticles

The search for new plasmonic materials that are low-cost, chemically and thermally stable, and exhibit low optical losses has garnered significant attention among researchers. Recently, metal nitrides have emerged as promising alternatives to conventional, noble-metal-based plasmonic materials, such as silver and gold. Many of the initial studies on metal nitrides have focused on computational prediction of the plasmonic properties of these materials. In recent years, several synthetic methods have been developed to enable empirical analysis. This review highlights synthetic techniques for the preparation of plasmonic metal nitride nanoparticles, which are predominantly free-standing, by using solid-state and solid–gas phase reactions, nonthermal and arc plasma methods, and laser ablation. The physical properties of the nanoparticles, such as shape, size, crystallinity, and optical response, obtained with such synthetic methods are also summarized.     

金纳米颗粒的水相法合成及荧光性能

在水溶液中,以PAMAM树形分子为模板,乙醇为还原剂,制备了树形分子包裹的金纳米颗粒,其水溶性好,可以稳定放置1年以上;通过控制Au3+与PAMAM树形分子的摩尔比,可以得到粒径可控的金纳米颗粒,其粒径范围为1～4nm,分别在385和402nm处出现强的共振瑞利光散射峰和荧光峰.室温下,荧光量子产率达到10%以上,比其它文献报道的金纳米颗粒的荧光量子产率高2个数量级以上,这一特性使其在潜指纹识别、光催化等方面具有很大的应用潜力.     

Activation of Oxygen on Gold and Silver Nanoparticles Assisted by Surface Plasmon Resonances

Surface plasmon resonances (SPRs) have been found to promote chemical reactions. In most oxidative chemical reactions oxygen molecules participate and understanding of the activation mechanism of oxygen molecules is highly important. For this purpose, we applied surface‐enhanced Raman spectroscopy (SERS) to find out the mechanism of SPR‐assisted activation of oxygen, by using p‐aminothiophenol (PATP), which undergoes a SPR‐assisted selective oxidation, as a probe molecule. In this way, SPR has the dual function of activating the chemical reaction and enhancing the Raman signal of surface species. Both experiments and DFT calculations reveal that oxygen molecules were activated by accepting an electron from a metal nanoparticle under the excitation of SPR to form a strongly adsorbed oxygen molecule anion. The anion was then transformed to Au or Ag oxides or hydroxides on the surface to oxidize the surface species, which was also supported by the heating effect of the SPR. This work points to a promising new era of SPR‐assisted catalytic reactions.     

Mechanism of Producing Metallic Nanoparticles,with an Emphasis on Silver and Gold Nanoparticles,Using Bottom-Up Methods

Bottom-up nanoparticle (NP) formation is assumed to begin with the reduction of the precursor metallic ions to form zero-valent atoms. Studies in which this assumption was made are reviewed. The standard reduction potential for the formation of aqueous metallic atoms—E⁰(Mⁿ⁺_aq/M⁰_aq)—is significantly lower than the usual standard reduction potential for reducing metallic ions Mⁿ⁺ in aqueous solution to a metal in solid state. E⁰(Mⁿ⁺_aq/M⁰_solid). E⁰(Mⁿ⁺_aq/M⁰_aq) values are negative for many typical metals, including Ag and Au, for which E⁰(Mⁿ⁺_aq/M⁰_solid) is positive. Therefore, many common moderate reduction agents that do not have significantly high negative reduction standard potentials (e.g., hydrogen, carbon monoxide, citrate, hydroxylamine, formaldehyde, ascorbate, squartic acid, and BH₄⁻), and cannot reduce the metallic cations to zero-valent atoms, indicating that the mechanism of NP production should be reconsidered. Both AgNP and AuNP formations were found to be multi-step processes that begin with the formation of clusters constructed from a skeleton of M⁺-M⁺ (M = Ag or Au) bonds that is followed by the reduction of a cation M⁺ in the cluster to M⁰, to form M_n⁰ via the formation of NPs. The plausibility of M⁺-M⁺ formation is reviewed. Studies that suggest a revised mechanism for the formation of AgNPs and AuNPs are also reviewed.     

Metal Dendrimers: Synthesis of Hierarchically Stellated Nanocrystals by Sequential Seed‐Directed Overgrowth

Hierarchically organized structures are prevalent in nature, where such features account for the adhesion properties of gecko feet and the brilliant color variation of butterfly wings. Achieving artificial structures with multiscale features is of interest for metamaterials and biomimetic applications. However, the fabrication of such structures relies heavily on lithographic approaches, although self‐assembly routes to superstructures are promising. Sequential seed‐directed overgrowth is now demonstrated as a route to metal dendrimers, which are hierarchically branched nanocrystals (NCs) with a three‐dimensional order analogous to that of molecular dendrimers. This method was applied to a model Au/Pd NC system; in general, the principle of sequential seed‐directed overgrowth should enable the synthesis of new hierarchical inorganic structures with high symmetry.     

Structure and Properties of Electrochemically Synthesized Silver Nanoparticles in Aqueous Solution by High-Resolution Techniques

The aim of this work was to deeply investigate the structure and properties of electrochemically synthesized silver nanoparticles (AgNPs) through high-resolution techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), Zeta Potential measurements, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). Strong brightness, tendency to generate nanoclusters containing an odd number of atoms, and absence of the free silver ions in solution were observed. The research also highlighted that the chemical and physical properties of the AgNPs seemed to be related to their peculiar oxidative state as suggested by X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRPD) analyses. Finally, the MTT assay tested the low cytotoxicity of the investigated AgNPs.     

DNA‐Encoded Tuning of Geometric and Plasmonic Properties of Nanoparticles Growing from Gold Nanorod Seeds

Systematically controlling the morphology of nanoparticles, especially those growing from gold nanorod (AuNR) seeds, are underexplored; however, the AuNR and its related morphologies have shown promises in many applications. Herein we report the use of programmable DNA sequences to control AuNR overgrowth, resulting in gold nanoparticles varying from nanodumbbell to nanooctahedron, as well as shapes in between, with high yield and reproducibility. Kinetic studies revealed two representative pathways for the shape control evolving into distinct nanostructures. Furthermore, the geometric and plasmonic properties of the gold nanoparticles could be precisely controlled by adjusting the base compositions of DNA sequences or by introducing phosphorothioate modifications in the DNA. As a result, the surface plasmon resonance (SPR) peaks of the nanoparticles can be fine‐tuned in a wide range, from visible to second near‐infrared (NIR‐II) region beyond 1000 nm.     

Sonochemical Synthesis of Gold Nanoparticles by Using High Intensity Focused Ultrasound

The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high‐intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au³⁺ to Au⁰ by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size‐ and shape‐controlled metal nanoparticles.     

金纳米颗粒等离子体共振吸收光谱检测头孢唑啉

根据金纳米粒子等离子体共振吸收引起的溶液颜色变化,建立了一种快速、简便检测头孢唑啉的色度分析方法.方法线性范围为0.1～5.0 μmol/L,检测限为14 nmol/L.将该方法用于头孢唑啉钠粉针剂的分析,回收率在97.4％～100.2％之间,相对标准偏差小于6.1％.     

Surface and Structural Properties of Gold Nanoparticles and Their Biofunctionalized Derivatives in Aqueous Electrolytes Solution

Gold nanoparticles reduced by sodium citrate (d ～ 10 nm) and purchased gold colloid particles (d ～ 500 nm) were examined and compared. The properties of both gold particles and their biofunctionalized derivatives with L-cysteine and L-glutathione were studied in the presence of sodium nitrate. The structural investigations indicated an aggregated inner structure.

The isoelectric points of pure gold, citrate reduced gold, and functionalized gold were measured and compared. The low isoelectric point of pure gold/water interface was explained by considering the distribution and accumulation of H⁺ and OH^? ions within the interfacial water layer, being more pronounced for OH^? ions.      

过氧化氢溶液中单和双金属金-银纳米粒子氧化L-亮氨酸的动力学(英文)

The catalytic activity of surfactant stabilized mono-and bimetallic Au and Ag nanoparticles for the oxidation of an amino acid,L-leucine,was studied using hydrogen peroxide as the oxidant.The Au and Ag nanoparticle catalysts exhibited very good catalytic activity and the kinetics of the reaction were found to be pseudo-first order with respect to the amino acid.The effects of several factors,such as oxidant concentration,ionic strength,pH,and catalyst concentration on the reaction,were also investigated.In particular,optimal oxidant and catalyst concentrations were determined.Very high concentrations of the metal nano-catalysts or the oxidant led to a dramatic increase in reaction rate.Moreover,bimetallic Au-Ag catalysts provided higher selectivity than pure Au or Ag.     

Oxidative Dissolution of Silver Nanoparticles by Dioxygen: A Kinetic and Mechanistic Study

We have recently reported a kinetic and mechanistic study on oxidative dissolution of silver nanoparticles (AgNPs) by H₂O₂. In the present study, the parameters that govern the dissolution of AgNPs by O₂ were revealed by using UV/Vis spectrophotometry. Under the same reaction conditions (Tris‐HOAc, pH 8.5, I=0.1 M at 25 °C) the apparent dissolution rate (k_app) of AgNPs (10±2.8 nm) by O₂ is about 100‐fold slower than that of H₂O₂. The reaction rate is first‐order with respect to [Ag⁰], [O₂], and [Tris]_T, and inverse first‐order with respect to [Ag⁺] (where [Ag⁰]=total concentration of Ag metal and [Tris]_T=total concentration of Tris). The rate constant is dependent on the size of AgNPs. No free superoxide (O₂⁻) and hydroxyl radical (⋅OH) were detected by trapping experiments. On the basis of kinetic and trapping experiments, an amine‐activated pathway for the oxidation of AgNPs by O₂ is proposed.     

银/铂双金属中空纳米颗粒的制备及光学性质研究

通过以Ag纳米颗粒为模板的置换和沉积反应,制备了Ag/Pt双金属复合纳米颗粒.用透射电子显微镜(TEM)对颗粒的形貌、尺寸和结构进行了表征,发现复合颗粒具有中空结构.紫外可见吸收光谱(UV-Vis)研究表明,Ag/Pt双金属中空复合纳米颗粒具有单峰的表面等离子共振吸收特征,随着反应溶液中氯铂酸和硝酸银摩尔比的增加,吸收峰先红移后蓝移.表面增强拉曼光谱实验结果表明,Ag/Pt双金属复合纳米颗粒对吡啶分子具有较好的增强效果.     

Plasmonic Properties and Size Programming: A Quantitative Study for Photosynthesized Gold Nanoparticles

A novel two‐component peak quantitative spectra deconvolution model is employed to elucidate the relationship between the plasmonic properties and the concentration‐dependent Au nanocrystals nucleation. The reactions with the initial concentration of starting reagent NaAuCl₄ from 0.75 mM to 0.1 mM are monitored. The peak area variation between component peak (b), large size nanoparticles (d ≥ 8.1 nm), and component peak (a), small size nanoparticles (d ≤ 8.0 nm), demonstrates that the initial concentration of NaAuCl₄ plays a decisive factor to determine the (b/a) ratio, i.e. the growth progresses of Au nanoparticles. If the initial concentration of NaAuCl₄ is higher than 0.2 mM, two independent growth progresses of Au nanoparticles are observed, and a continuous λ_max blue‐shift of surface plasmon absorption peak accompanied with the second growth progress is measured. On the other hand, in the reactions with the initial concentration of NaAuCl₄ lower than 0.2 mM, only one crystal growth progress of Au nanoparticles is shown, and the blue‐shift phenomenon of absorption peak induced by the second crystal growth progress no longer exists.     

纳米银刻蚀比色法检测褪黑激素

该文构建了一种基于氯金酸刻蚀球形纳米银检测褪黑激素的简单、高灵敏比色探针。纳米银可被氯金酸氧化刻蚀为Ag+,同时还原生成的纳米金沉积在刻蚀后的纳米银表面,导致其溶液的吸光度降低和颜色增强(由黄色变为橘黄色)。当向体系中加入褪黑激素时,氯金酸被还原,抑制了纳米银的刻蚀,从而使得溶液吸光度增加和颜色变浅。结果显示,在0.1 nmol/L~1.0 mmol/L范围内,褪黑激素浓度对数值(lgC)与其吸光度改变值(ΔA)呈良好的线性关系,线性方程为ΔA=0.049 8+0.516lgC,相关系数(R2)为0.996 4,检出限为0.09 nmol/L。该方法成功应用于人体尿液和葡萄中的褪黑激素的测定。