Gold nanoparticle/charged silsesquioxane films immobilized onto Al/SiO2 surface applied on the electrooxidation of nitrite

In this work, gold nanoparticles lower than 10?nm were prepared in an aqueous medium using two charged silsesquioxanes, the propylpyridinium chloride and propyl-1-azonia-4-azabicyclo[2.2.2]octane chloride, as stabilizer agents which revealed to be water-soluble. This stabilization method is innovative allowing thin films containing gold nanoparticles to be obtained, and it was used for the first time in the preparation of carbon paste electrodes (CPEs). The charged silsesquioxanes were characterized by liquid ¹³C NMR. The gold nanoparticle/silsesquioxane systems were characterized by ultraviolet–visible spectroscopy (UV–Vis) and transmission electron microscopy. In sequence, they were immobilized on silica matrix coated with aluminum oxide. The resulting solid materials designated as Au-Py/AlSi and Au-Db/AlSi were characterized by infrared spectroscopy and N₂ adsorption/desorption isotherms. The results showed that the gold nanoparticle/silsesquioxane systems are strongly adhered to the surface-forming thin films. The Au-Py/AlSi and Au-Db/AlSi materials were used to prepare CPEs for the electrooxidation of nitrite (NO ₂ ^? ) using cyclic voltammetry and differential pulse voltammetry. The Au-Py/AlSi and Au-Db/AlSi CPEs showed high sensitivity and detection limits of 71.87 and 53.66?μA?mmol^–1?L and 1.3 and 3.0?μmol?L^–1, respectively.     

Fabrication and Characterization of Iron (II,III) on Positively Charged Gold Nanoparticles with Application for Magnetically Recoverable Catalysis

An aqueous dispersion was prepared by attaching positively charged gold nanoparticles to the surface of poly-sodium-p-styrenesulfonate-modified Fe₃O₄ nanoparticles. The Fe₃O₄@positively charged gold nanoparticles offer high monodispersion, stability against aggregation, and high magnetization with uniform size. The Fe₃O₄@positively charged gold nanoparticles were efficient and recyclable catalysts due to the formation of a positively charged gold layer on the surface of Fe₃O₄ nanoparticles and were stable in aqueous solution for over forty-eight hours and hence may have a broad range of applications.     

Preparation of sterically stabilized gold nanoparticles for plasmonic applications

Plasmonic nanoparticles such as those of gold or silver have been recently investigated as a possible way to improve light absorption in thin film solar cells. Here, a simple method for the preparation of spherical plasmonic gold nanoparticles in the form of a colloidal solution is presented. The nanoparticle diameter is controlled in the range from several nm to tens of nm depending on the synthesis parameters with the size dispersion down to 14 %. The synthesis is based on thermal decomposition and reduction of the chloroauric acid in the presence of a stabilizing capping agent (surfactant) that is very slowly injected into the hot solvent. The surfactant prevents uncontrolled nanoparticle aggregation during the growth process. The nanoparticle size and shape depend on the type of the stabilizing agent. Surfactants with different lengths of the hydrocarbon chains such as Z-octa-9-decenylamine (oleylamine) with AgNO₃ and polyvinylpyrrolidone with AgNO₃ were used for the steric stabilization. Hydrodynamic diameter of the gold nanoparticles in the colloidal solution was determined by dynamic light scattering while the size of the nanoparticle metallic core was found by small-angle X-ray scattering. The UV-VIS-NIR spectrophotometer measurements revealed a plasmon resonance absorption in the 500–600 nm range. Self-assembled nanoparticle arrays on a silicon substrate were prepared by drop casting followed by spontaneous evaporation of the solvent and by a modified Langmuir-Blodgett deposition. The degree of perfection of the self-assembled arrays was analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering. Homogeneous close-packed hexagonal ordering of the nanoparticles stretching over large areas was evidenced. These results document the viability of the proposed nanoparticle synthesis for the preparation of high-quality plasmonic templates for thin film solar cells with enhanced power conversion efficiency, surface enhanced Raman scattering, and other applications.     

Controlled nanoparticle assembly by dewetting of charged polymer solutions

In this paper, we present an alternative approach for controlled nanoparticle organization on a solid substrate by applying dewetting patterns of charged polymer solutions as a templating system. Thin films of charged polymer solutions dewet a solid substrate to form complex dewetting patterns that depend on the polymer charge density. These patterns, ranging from polygonal networks to elongated structures that are stabilized by viscous forces during dewetting, serve as potential templates for two-dimensional nanoparticle organization on a solid substrate. Thus, while nanoparticles dried in pure water undergo self-assembly to form close-packed arrays, addition of charged polymer in the dispersion leads to the formation of open structures that are directed by the dewetting patterns of the polymer solution. In this study, we focus on the application of elongated structures resulting from dewetting of high-charge-density polymer solutions to align nanoparticles of silica and gold into long chains that are several micrometers in length. The particle ordering process is a two-step mechanism: an initial confinement of the nanoparticles in the dewetting structures and self-assembly of the particles within these structures upon further drying by lateral capillary attractions.     

Absorption,fluorescence and resonance Rayleigh scattering spectral characteristics of interaction of gold nanoparticle with safranine T

Gold nanoparticle is an important nanomaterial and has been investigated widely owing to its special physical and chemical property[1―5]. In recent years it has been found that the multiple-component nano- structure assembly containing metal, semiconduct…     

Bimetallic Cu–Pt/nanoporous carbon composite as an efficient catalyst for methanol oxidation

A novel bimetallic Cu–Pt nanoparticle supported onto Cu/indirectly carbonized nanoporous carbon composite (Cu–Pt/ICNPCC) was prepared through a two-step process: first, carbonization of furfuryl alcohol-infiltrated MOF-199 [metal–organic framework Cu₃(BTC)₂ (BTC?=?1,3,5-benzene tricarboxylate)], without removing the Cu metal with HF aqueous solution; second, the partial galvanic replacement reaction (GRR) of Cu nanoparticles by Pt^IV upon immersion in a platinum(IV) chloride solution. The synthesized materials characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods. The EDS result revealed that part of Cu nanoparticles have been substituted by Pt nanoparticles after GRR. The methanol oxidation at the surface of Cu–Pt/ICNPCC was investigated by cyclic voltammetry method in 0.5 M H₂SO₄ and indicated good electro-catalytic activity towards methanol oxidation (E_p?=?0.85 V vs. NHE and j_f?=?1.00 mA cm^?2). It is suggested that this improvement is attributed to the effect of proper Cu/ICNPCC for fine dispersion, efficient adhesion, and prevention of Pt coalescing.     

Electrochemistry of metal nanoparticles: the effect of substrate

It is shown that nanoparticles localized on a foreign solid electrode may display two opposite shifts of dissolution potential, namely, a shift toward either more positive or more negative values as compared with the equilibrium potential of M ⁿ⁺/M ⁰ or the potential of bulk metal electrooxidation. The observed phenomena are interpreted in view of three energy states of substance, which are realized depending on contribution of the surface Gibbs free energy (ΔG°) to the energy of the system. Literature data concerning different metal-substrate pairs and specially conducted experimental investigations of electrooxidation of gold nanoparticles (radius equal to 10 and 150?nm), which are localized on the surface of glassy carbon, bulk gold, and platinum electrodes are presented and discussed. A shift of maximum current potential of small nanoparticles oxidation toward more positive values is observed in this series. The oxidation potential of large nanoparticles is not affected by the nature of the substrate. In all cases, electrooxidation of gold nanoparticles occurs at the more negative potentials than those of the bulk gold electrooxidation. It is shown that depending on the nature of the substrate and nanoparticle size, the dominating effect is either interaction of nanoparticles with the substrate (ΔG°?<?0) and electrochemical potential shifts toward positive values or impact of surface Gibbs free energy of nanoparticles (ΔG°?>?0) into energy of the system and electrochemical potential shifts toward negative values. The validity of the proposed assumptions is confirmed by good correlation of literature and our experimental data with calculated ones.     

Detection of DNA immobilized on bare gold electrodes and gold nanoparticle-modified electrodes via electrogenerated chemiluminescence using a ruthenium complex as a tag

Electrogenerated chemiluminescence (ECL) for DNA hybridization detection is demonstrated based on DNA that was self-assembled onto a bare gold electrode and onto a gold nanoparticles modified gold electrode. A ruthenium complex served as an ECL tag. Gold nanoparticles were self-assembled on a gold electrode associated with a 1,6-hexanedithiol monolayer. The surface density of single stranded DNA (ssDNA) on the gold nanoparticle modified gold electrode was 4.8?×?10¹⁴ molecules per square centimeter which was 12-fold higher than that on the bare gold electrode. Hybridization was induced by exposure of the target ssDNA gold electrode to the solution of ECL probe consisting of complementary ssDNA tagged with ruthenium complex. The detection limit of target ssDNA on a gold nanoparticle modified gold electrode (6.7?×?10^?12 mol L^?1) is much lower than that on a bare gold electrode (1.2?×?10^?10 mol L^?1). The method has been applied to the detection of the DNA sequence related to cystic fibrosis. This work demonstrates that employment of gold nanoparticles self-assembled on a gold electrode is a promising strategy for the enhancement of the sensitivity of ECL detection of DNA.     

聚苯胺包裹的金纳米粒子的合成和表征及初步应用

用苯胺作还原剂还原氯金酸合成了金纳米结构. TEM实验表明, 苯胺还原氯金酸能生成苯胺齐聚物或其聚合物包裹的金球形纳米粒子. XPS分析表明, 金纳米粒子包覆的聚合物层带正电荷. 该纳米粒子能用于电极表面纳米结构组装及氧化还原性的生物大分子的电化学研究, 实现了超氧化物歧化酶(SOD)在这种带正电荷的金纳米粒子表面的直接电子转移.     

Synthesis of radioactive gold nanoparticle in surfactant medium

The present study describes the synthesis of radioactive gold nanoparticle in surfactant medium. Proton irradiated stable ¹⁹⁷Au and radioactive ¹⁹⁸Au were simultaneously used for production of radioactive gold nanoparticle. Face centered cubic gold nanoparticles with size of 4–50 nm were found in proton irradiated gold foil. However, the size of nanoparticle varies with pH using both stable and radioactive gold.     

Synthesis and Catalytic Reactions of Nanoparticles formed by Electrospray Ionization of Coinage Metals

Noble metals can be ionized by electrochemical corrosion and transported by electrospray ionization. Mass spectrometry (MS) showed solvated metal ions as the main ionic constituent of the sprayed droplets. Collection of the electrospray plume on a surface yielded noble metal nanoparticles (NPs) under ambient conditions. The NPs were characterized by several techniques. Under typical conditions, capped‐nanoparticle sizes averaged 2.2 nm for gold and 6.5 nm for silver. The gold nanoparticles showed high catalytic activity in the reduction of p‐nitrophenol by NaBH₄. Efficient catalysis was also observed by simply directing the spray of solvated Au⁺ onto the surface of an aqueous p‐nitrophenol/NaBH₄ mixture. Organometallic ions were generated by spiking ligands into the spray solvent: for example, Cu^I bipyridine cations dominated the spray during Cu electrocorrosion in acetonitrile containing bipyridine. This organometallic reagent was shown to be effective in the radical polymerization of styrene.     

A Green Approach for Synthesis of Gold and Silver Nanoparticles by Leishmania sp.

The application of microorganisms for the synthesis of metal nanoparticles as an eco-friendly and promising approach is ongoing. In this paper, an attempt has been made to investigate the capability of Leishmania sp. for synthesis of metal nanoparticles from aqueous silver and gold ions. The samples were analyzed by a UV?CVis spectroscopy and the results showed the absorbance peak values at 420 and 540?nm, respectively, for the surface plasmon resonance of silver and gold nanoparticles. The surface morphology of the nanoparticles in solution was visualized by atomic force microscope and scanning electron microscope images, which showed the production of metallic nanoparticles by this protozoan. Fourier transform infrared spectroscopy analyses confirmed the presence of different bands of protein as capping and stabilizing agent on the nanoparticles surfaces. The synthesized silver and gold nanoparticles were with dimensions ranging between 10 and 100?nm for silver and 50?C100?nm for gold. These results of the present study have demonstrated the efficiency of this protozoan for synthesis of nanoparticles, by offering the merits of environmentally friendly, amenability, and time saving for large-scale production.     

Investigation of the electrochemical and electrocatalytic behavior of positively charged gold nanoparticle and L-cysteine film on an Au electrode

Positively charged gold nanoparticle (positively charged nano-Au), which was prepared, characterized by ξ-potential and transmission electron microscopy (TEM) was used in combination with l-cysteine to fabricate a modified electrode for electrocatalytic reaction of biomolecules. Compared with electrodes modified by negatively charged gold nanoparticle/l-cysteine, or l-cysteine alone, the electrode modified by the positively charged gold nanoparticle/l-cysteine exhibited excellent electrochemical behavior toward the oxidation of biomolecules such as ascorbic acid, dopamine and hydrogen peroxide. Moreover, the proposed mechanism for electrocatalytic response of positively charged gold nanoparticle was discussed. The immunosensor showed a specific to ascorbic acid in the range 5.1 × 10⁻⁷-6.7 × 10⁻⁴ M and a low detection limit of 1.5 × 10⁻⁷ M. The experimental results demonstrate that positively charged gold nanoparticle have more efficient electrocatalytic reaction than negatively charged gold nanoparticle, which opens up new approach for fabricating sensor.     

金纳米粒子表面自组装巯基十一烷醇单分子层体系的制备及其光散射特性研究

采用柠檬酸钠还原法制备了水相金纳米粒子, 通过巯基的自组装, 成功获得了巯基十一烷醇(MUN)单分子层保护的金纳米粒子. 用紫外可见光谱、透射电子显微镜、激光散射粒度分析、同步散射光谱和发射光谱等手段对组装前后的金纳米粒子的性质进行了研究. 结果表明: 制备的金纳米粒子最大吸收波长518 nm, 形状规则, 粒度均匀, 平均粒径为14.6 nm, 每个粒子含有约9.64×10⁴原子; 组装之后的金纳米粒子表面等离子体共振吸收峰红移17.0 nm, 平均粒径增大为20.2 nm, 组装层的平均厚度2.8 nm, 与MUN分子长度相当, 结合量实验证明每一个金纳米粒子可以结合约7.52×10³个MUN, 表面覆盖率为83.6%, 粒子分散均匀, 稳定性增强可长期保存; 同步散射光谱变化和发射光谱中分频、差频和倍频峰的存在证明, 金纳米粒子组装前后均具有非线性光学特性.     

Ambient microdroplet annealing of nanoparticles

Conversion of polydisperse nanoparticles to their monodisperse analogues and formation of organized superstructures using them involve post synthetic modifications, and the process is generally slow. We show that ambient electrospray of preformed polydisperse nanoparticles makes them monodisperse and the product nanoparticles self-assemble spontaneously to form organized films, all within seconds. This phenomenon has been demonstrated with thiol-protected polydisperse silver nanoparticles of 15 ± 10 nm diameter. Uniform silver nanoparticles of 4.0 ± 0.5 nm diameter were formed after microdroplet spray, and this occurred without added chemicals, templates, and temperature, and within the time needed for electrospray, which was of the order of seconds. Well organized nanoparticle assemblies were obtained from such uniform particles. A home-made and simple nanoelectrospray set-up produced charged microdroplets for the generation of such nanostructures, forming cm² areas of uniform nanoparticles. A free-standing thin film of monodisperse silver nanoparticles was also made on a liquid surface by controlling the electrospray conditions. This unique method may be extended for the creation of advanced materials of many kinds.

Polydisperse silver nanoparticles were converted to a highly ordered assembly of nanoparticles by microdroplet-induced chemistry, under ambient conditions, within seconds.     

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene with microsphere sizes of 100, 300, 500, and 1410 nm under the action of monochromatic light with an excitation wavelength of 254 nm was studied. Preliminary irradiation of the polymer dispersion induces formation of gold particles under dark conditions. Dependences of gold nanoparticles formation on the duration of preliminary polymer irradiation and concentration of introduced HAuCl₄ aqueous solution were determined. A mechanism of the polystyrene-assisted formation of gold nanoparticles was proposed. The size and structure of gold nanoparticles were determined.     

Biosynthesis of silver and gold nanoparticles using Sargassum horneri extract as catalyst for industrial dye degradation

This study focuses on the green synthesis of silver and gold nanoparticles using the marine algae extract, Sargassum horneri, as well as the degradation of organic dyes using biosynthesized nanoparticles as catalysts. The phytochemicals of the brown algae Sargassum horneri acted as reducing and capping agents for nanoparticle synthesis. Ultraviolet–visible absorption spectroscopy, dynamic light scattering, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy were used to characterize the biosynthesized nanoparticles. The green-synthesized SH-AgNPs and SH-AuNPs exhibited high catalytic activity for degradation of organic dyes, such as methylene blue, rhodamine B, and methyl orange. The reduction reactions of dyes are based on pseudo-first-order kinetics.     

Rapid Cationization of Gold Nanoparticles by Two‐Step Phase Transfer

Cationic gold nanoparticles offer intriguing opportunities as drug carriers and building blocks for self‐assembled systems. Despite major progress on gold nanoparticle research in general, the synthesis of cationic gold particles larger than 5 nm remains a major challenge, although these species would give a significantly larger plasmonic response compared to smaller cationic gold nanoparticles. Herein we present the first reported synthesis of cationic gold nanoparticles with tunable sizes between 8–20 nm, prepared by a rapid two‐step phase‐transfer protocol starting from simple citrate‐capped particles. These cationic particles form ordered self‐assembled structures with negatively charged biological components through electrostatic interactions.     

Development of uncoated near-spherical gold nanoparticles for the label-free quantification of Lactobacillus rhamnosus GG by surface-enhanced Raman spectroscopy

The Surface-enhanced Raman spectroscopy (SERS) method based on gold nanoparticles as SERS substrate was investigated for the label-free detection and quantification of probiotic bacteria that are widely used in various pharmaceutical formulations. Indeed, the development of a simple and fast SERS method dedicated to the quantification of bacteria should be very useful for the characterization of such formulations in a more convenient way than the usually performed tedious and time-consuming conventional counting method. For this purpose, uncoated near-spherical gold nanoparticles were developed at room temperature by acidic treatment of star-like gold nanoparticle precursors. In this study, we first investigated the influence of acidic treatment conditions on both the nanoparticle physicochemical properties and SERS efficiency using Rhodamine 6G (R6G) as “model” analyte. Results highlighted that an effective R6G Raman signal enhancement was obtained by promoting chemical effect through R6G-anion interactions and by obtaining a suitable aggregation state of the nanoparticles. Depending on the nanoparticle synthesis conditions, R6G SERS signals were up to 10²–10³-fold greater than those obtained with star-like gold nanoparticles. The synthesized spherical gold nanoparticles were then successfully applied for the detection and quantification of Lactobacillus rhamnosus GG (LGG). In that case, the signal enhancement was especially due to the combination of anion-induced chemical enhancement and nanoparticle aggregation on LGG cell wall consecutive to non-specific interactions. Both the simplicity and speed of the procedure, achieved under 30 min, including nanoparticle synthesis, sample preparation, and acquisition of SERS spectra, appeared as very relevant for the characterization of pharmaceutical formulations incorporating probiotics.

Graphical abstract

     

The green synthesis of fine particles of gold using an aqueous extract of <Emphasis Type="Italic">Monotheca buxifolia</Emphasis> (Flac.)

This study deals with the synthesis and physicochemical investigation of gold nanoparticles using an aqueous extract of Monotheca buxifolia (Flac.). On the treatment of aqueous solution of tetrachloroauric acid with the plant extract, gold nanoparticles were rapidly fabricated. The synthesized particles were characterized by UV–Vis spectrophotometry (UV), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDX) and Scanning electron microscopy (SEM). The formation of AuNPs was confirmed by noting the change in color through visual observations as well as via UV–Vis spectroscopy. UV?Vis spectrum of the aqueous medium containing gold nanoparticles showed an absorption peak at around 540 nm. FTIR was used to identify the chemical composition of gold nanoparticles and Au-capped plant extract. The presence of elemental gold was also confirmed through EDX analysis. SEM analysis of the gold nanoparticles showed that they have a uniform spherical shape with an average size in the range of 70–78 nm. This green system showed to be better capping and stabilizing agent for the fine particles. Further, the antioxidant activity of Monotheca buxifolia (Flac.) extract and Au-capped with the plant extract was also evaluated using FeCl₃/K₃[Fe(CN)]₆ in vitro assay.