Green synthesis of Au nanoparticles immobilized on halloysite nanotubes for surface-enhanced Raman scattering substrates

A facile and green route was introduced to synthesize Au nanoparticles immobilized on halloysite nanotubes (AuNPs/HNTs) used for surface-enhanced Raman scattering substrates. The naturally occurring HNTs were firstly functionalized with a large amount of -NH(2) groups by N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (AEAPTES), which possesses one lone electron pair and will "anchor" Au ions to form a chelate complex. Then, with the addition of tea polyphenols (TP), the Au ions were reduced on the surface of the previously formed Au-NH(2) chelate complex to form AuNPs. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) observations indicate that a large amount of AuNPs were synthesized on HNTs. The AuNPs are irregularly spherical and densely dispersed on HNTs and the diameter of the nanoparticles varies from 20 to 40 nm. The interactions between AuNPs and -NH(2) groups were verified by X-ray photoelectron spectroscopy (XPS) and the results showed that the functional groups can "anchor" AuNPs through the chelating effect. The as-prepared AuNPs/HNTs nanomaterials with several nanometers gaps among nanoparticles were used as a unique surface-enhanced Raman scattering substrate, which possessed strong and distinctive Raman signals for R6G, indicating the remarkable enhancement effect of the AuNPs/HNTs.     

Facile synthesis of gold nanoparticles with narrow size distribution by using AuCl or AuBr as the precursor

Gold(I) halides, including AuCl and AuBr, were employed for the first time as precursors in the synthesis of Au nanoparticles. The synthesis was accomplished by dissolving Au(I) halides in chloroform in the presence of alkylamines, followed by decomposition at 60 degrees C. The relative low stability of the Au(I) halides and there derivatives eliminated the need for a reducing agent, which is usually required for Au(III)-based precursors to generate Au nanoparticles. Controlled growth of Au nanoparticles with a narrow size distribution was achieved when AuCl and oleylamine were used for the synthesis. FTIR and mass spectra revealed that a complex, [AuCl(oleylamine)], was formed through coordination between oleylamine and AuCl. Thermolysis of the complex in chloroform led to the formation of dioleylamine and Au nanoparticles. When oleylamine was replaced with octadecylamine, much larger nanoparticles were obtained due to the lower stability of [AuCl(octadecylamine)] complex relative to [AuCl(oleylamine)]. Au nanoparticles can also be prepared from AuBr through thermolysis of the [AuBr(oleylamine)] complex. Due to the oxidative etching effect caused by Br(-), the nanoparticles obtained from AuBr exhibited an aspect ratio of 1.28, in contrast to 1.0 for the particles made from AuCl. Compared to the existing methods for preparing Au nanoparticles through the reduction of Au(III) compounds, this new approach based on Au(I) halides offers great flexibility in terms of size control.     

Photocatalytic Synthesis of Gold Nanoparticles Using Preyssler Acid and Their Photocatalytic Activity

Preyssler acid H14[NaP5W30O110] was used as reducing agent and stabilizer for the synthesis of gold nanoparticles by photolysis of Au(III)/Preyssler acid/propan-2-ol solution.Preyssler acid plays both the role of transferring electrons from propan-2-ol to Au(III) and stabilizing the nanoparticles.Propan-2-ol was used as sacrificial reagent for the photoformation of reduced Preyssler acid.Gold nanoparticles (Au NPs) were characterized by UV-Vis spectroscopy,transmission electron microscopy (TEM),and particle size distribution (PSD) measurements.The synthesized Au NPs had a uniform hexagonal morphology and their size was about 17 nm.The catalytic performance of these NPs for photodegradation of methyl orange (MeO) was investigated in aqueous solution.UV-Vis studies showed that Au NPs can catalyze photodegradation of this azo dye.The pseudo-first-order rate constants were also calculated for this reaction.     

分子印迹聚合物负载纳米金催化剂的制备及其底物识别性能

以4-硝基苯甲醇与氯金酸的络合物为模板,利用聚合物空腔内胺基捕获NaBH4还原的纳米粒子,设计和制备了一种具有底物识别性能的分子印迹聚合物负载纳米Au催化剂(Au/MIP).运用红外光谱、紫外-可见光谱和扫描电镜等方法对催化剂进行了表征.同时以水为溶剂,过氧化氢为氧化剂,考察了催化剂在取代苯甲醇氧化反应中的催化性能.结...     

SYNTHESIS OF POLY(DIVINYLBENZENE-co-ACRYLIC ACID) HOLLOW MICROSPHERES WITH GOLD NANOPARTICLES ON THE INTERIOR SURFACE

Poly(divinylbenzene-co-acrylic acid) (poly(DVB-co-AA)) hollow microspheres with gold nanoparticles on the interior surfaces were prepared from the gold nanoparticles-coated poly(methacrylic acid) (PMAA@Au@poly(DVB-co-AA)) core-shell microspheres by removal of the PMAA core in water.Au nanoparticles-coated PMAA microspheres were afforded by the in-situ reduction of gold trichloride with PMAA microsphere as stabilizer via the interaction between carboxylic acid groups and Au nanoparticles.Gold nanoparticle...     

Voltammetric monitoring of gold nanoparticle formation facilitated by glycyl-L-tyrosine: relation to electronic spectra and transmission electron microscopy images

Voltammetric techniques have been introduced to monitor the formation of gold nanoparticles produced via the reaction of the amino acid glycyl-L-tyrosine with Au(III) (bromoaurate) in 0.05 M KOH conditions. The alkaline conditions facilitate amino acid binding to Au(III), inhibit the rate of reduction to Au(0), and provide an excellent supporting electrolyte for voltammetric studies. Data obtained revealed that a range of time-dependent gold solution species are involved in gold nanoparticle formation and that the order in which reagents are mixed is critical to the outcome. Concomitantly with voltammetric measurements, the properties of gold nanoparticles formed are probed by examination of electronic spectra in order to understand how the solution environment present during nanoparticle growth affects the final distribution of the nanoparticles. Images obtained by the ex situ transmission electron microscopy (TEM) technique enable the physical properties of the nanoparticles isolated in the solid state to be assessed. Use of this combination of in situ and ex situ techniques provides a versatile framework for elucidating the details of nanoparticle formation.     

A netlike DNA-templated Au nanoconjugate as the matrix of the direct electrochemistry of horseradish peroxidase

Herein, a novel DNA-templated Au nanoparticles (Au-DNA) nanoconjugate was prepared by using the combination of metallization and DNA compaction. The electrostatic interaction between Au(Ш) and the phosphate backbone of DNA formed the netlike coordination compound of Au(Ш)-DNA, and then the complex was chemically reduced to form Au nanoparticles in this network-like DNA conformation. The negatively charged nanoconjugate was used as the matrix for immobilization of horseradish peroxidase (HRP). A stable and well-defined redox peaks of HRP were observed on the Au-DNA nanoconjugate modified glassy carbon (GC) electrode, which indicated that the modified enzyme electrode displayed good direct electron transfer behavior and excellent reducing ability toward hydrogen peroxide (H₂O₂) with the apparent Michaelis–Menten constant (K_m) estimated to be 0.147 mM.     

Thermodynamically controlled separation of polyvalent 2-nm gold nanoparticle-oligonucleotide conjugates

We describe the synthesis of small (2-nm diameter) gold nanoparticles densely functionalized with thiolated DNA (DNA-Au NPs) and a method to separate these particles from excess free DNA after synthesis. The separation method utilizes the thermodynamically enhanced binding properties of 2-nm DNA-Au NPs, compared to free excess DNA, to selectively hybridize these small particles to larger (15-nm diameter) DNA-Au NPs and form aggregates that can be isolated by simple centrifugation. These 2-nm DNA-Au NPs are obtained in a 46% overall yield, have a high surface coverage of DNA (64.8 +/- 6.4 pmol/cm2), and as a result, exhibit increased melting temperatures and cooperative melting properties.     

A novel hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide/cysteamine-modified gold electrode

A novel strategy to fabricate a hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide nanocomposites/cysteamine-modified gold (Au) electrode was reported. The chitosan-graphene oxide nanocomposites were first assembled on a cysteamine-modified Au electrode to produce chitosan-graphene oxide/cysteamine/Au electrode. Then Ag nanoparticles were electrodeposited on the modified Au electrode and formed Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The chitosan-graphene oxide nanocomposites and the electrodeposited Ag nanoparticles were characterized by atomic force microscopy and scanning electron microscopy. The results showed the Ag nanoparticles were uniformly dispersed on the chitosan-graphene oxide/cysteamine/Au electrode. The cyclic voltammagrams and amperometric method were used to evaluate electrocatalytic properties of the Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The results showed that the modified electrode displayed good electrocatalytic activity to the reduction of hydrogen peroxide with a detection limit of 0.7 μM hydrogen peroxide based on a signal-to-noise ratio of 3. The sensor has good reproducibility, wide linear range, and long-term stability.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

Functionalized gold nanoparticles as phosphorescent nanomaterials and sensors

Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'-dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of approximately 340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands ( approximately 5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with Eu(III)/Tb(III) ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between Eu(III)/Tb(III) ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:Eu(III) complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:Tb(III) complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:Eu(III) complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca(2+), Mg(2+)) and transition metal ions (Cu(2+), Zn(2+), Ni(2+)), resulting from an isomorphous substitution of Eu(III) ions, whereas the luminescence intensity was not influenced by the addition of Na(+) and K(+) ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu(2+) ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles.     

电极/反相微乳液体系电沉积制备纳米金镀层

将含有氯化金的强酸性水溶液作为水相与Triton X-100、正己醇、正己烷组成反相微乳液体系, 并以该微乳液构成电极/反相微乳液电极系统, 利用电沉积方法成功地制备出纳米Au镀层. 循环伏安和交流阻抗对反相微乳液体系电沉积过程的研究发现, 微乳液中Au(III)的还原为完全不可逆过程, 其电化学反应的阻抗值约为具有相同表观浓度氯化金水溶液体系的5.5倍. SEM研究结果表明, 利用微乳液体系电沉积获得的金镀层由纳米Au颗粒组成, 直径为50 nm左右. 所制备的纳米Au修饰电极由于具有较大的比表面积, 其电化学性能优于纯Au电极, 该电极在酸性条件下有较好的析氢性能, 在碱性条件对丙三醇有较好的电催化氧化性能.     

Preparation and characterization of Ag(Au) bimetallic core–shell nanoparticles with new seed growth method

Ag(Au) bimetallic core–shell nanoparticles were prepared by a new seed growth method. Ascorbic acid was used to reduce the complex of HAuCl₄ and hexadecyltrimethylammoniumbromide (CTAB). This resulted in the forming of colorless Au(I) (AuCl₂⁻). It was used as the growth solution to prepare these bimetallic core–shell nanoparticles. These nanoparticles were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed these nanoparticles exhibited core–shell shape and there was large amount of Ag in the shell. These nanoparticles could be produced in a few minutes without violent stirring and the method was easy and convenient compared with others. The effect of amount of AuCl₂⁻ on the shape of nanoparticles was also studied. Many small gold nanoparticles were formed on the surface of bimetallic core–shell nanoparticles in the presence of excess AuCl₂⁻. The mechanisms were also proposed to explain the process of colloidal preparation.     

Photoinduced dissolution and redeposition of Au nanoparticles supported on TiO2

Au particles (mean size ca. 3 nm) supported on TiO(2) particles were irradiated by UV light (>300 nm) in aqueous solutions at 278 K. Photo-induced dissolution of Au nanoparticles followed by redeposition occurred in aqueous solutions containing halogen ions. The dissolution of Au nanoparticles yielded a Au(III) complex with a halogen ion; subsequent reduction of the Au(III) complex caused precipitation of larger Au particles on TiO(2).     

Nanoparticle-mediated electron transfer across ultrathin self-assembled films

The electrochemical behavior of arrays of Au nanoparticles assembled on Au electrodes modified by 11-mercaptoundecanoic acid (MUA) and poly-L-lysine (PLYS) was investigated as a function of the particle number density. The self-assembled MUA and PLYS layers formed compact ultrathin films with a low density of defects as examined by scanning tunneling microscopy. The electrostatic adsorption of Au particles of 19 +/- 3 nm on the PLYS layer resulted in randomly distributed arrays in which the particle number density is controlled by the adsorption time. In the absence of the nanoparticles, the dynamics of electron transfer involving the hexacynoferrate redox couple is strongly hindered by the self-assembled film. This effect is primarily associated with a decrease in the electron tunneling probability as the redox couple cannot permeate through the MUA monolayer at the electrode surface. Adsorption of the Au nanoparticles dramatically affects the electron-transfer dynamics even at low particle number density. Cyclic voltammetry and impedance spectroscopy were interpreted in terms of classical models developed for partially blocked surfaces. The analysis shows that the electron transfer across a single particle exhibits the same phenomenological rate constant of electron transfer as for a clean Au surface. The apparent unhindered electron exchange between the nanoparticles and the electrode surface is discussed in terms of established models for electron tunneling across metal-insulator-metal junctions.     

Biosynthesis of gold nanoparticles using Pseudomonas aeruginosa

Pseudomonas aeruginosa were used for extra-cellular biosynthesis of gold nanoparticles (Au NPs). Consequently, Au NPs were formed due to reduction of gold ion by bacterial cell supernatant of P. aeruginosa ATCC 90271, P. aeruginosa (2) and P. aeruginosa (1). The UV-vis and fluorescence spectra of the bacterial as well as chemical prepared Au NPs were recorded. Transmission electron microscopy (TEM) micrograph showed the formation of well-dispersed gold nanoparticles in the range of 15-30 nm. The process of reduction being extra-cellular and may lead to the development of an easy bioprocess for synthesis of Au NPs.     

The thermal behavior of Na[Au(CN)<Subscript>2</Subscript>] and the gold(I) dicyanaurate complex adsorbed on the activated carbon surface

The thermal behavior of crystalline Na[Au(CN)₂] and the gold(I) cyanide complex adsorbed from neutral aqueous solution of Na[Au(CN)₂] by the WSC-207C GR charcoal pre-washed from inorganic impurities was studied. The adsorption was established to lead to a significant decrease in the thermal stability of dicyanoaurate(I) anion. Using electron microscopy it was established that at the heating the adsorbent with the adsorbed [Au(CN)₂]-anions up to 300°C labile metallic gold nanoparticles were formed. Chemisorption nature of adsorption of the [Au(CN)₂]-anion by the activated carbon was assumed, and the nature of sorption sites involved in the formation of the primary bonds of gold(I) with the surface of the sorbent was considered.     

室温电子还原制备金纳米颗粒与琼脂糖复合膜的表征与应用

利用室温电子还原技术合成了一种金纳米颗粒与琼脂糖复合膜。合成过程采用氩气辉光放电为廉价电子源,方便快捷,绿色环保。通过紫外-可见(UV-Vis)分光光度计、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)仪、光电子能谱(XPS)等表征,发现可以通过改变氯金酸浓度调控复合膜中金纳米颗粒的分布,加入聚乙烯吡咯烷酮(PVP)可有效控制金纳米颗粒的形貌。由于复合膜具有金纳米颗粒密集排布的结构,可作为表面增强拉曼散射(SERS)活性基底。实验表明,以对氨基苯硫酚为探针,该复合膜作为SERS基底,SERS平均增强因子超过了106,检测限达到了10-12mol?L-1。除此之外,作为SERS基底,复合膜具有良好的均一性和稳定性。     

An Electrochemical Sensor Based on Gold Nanoparticles Incorporated in Mesoporous MFI Zeolite for Determination of Purine Bases in DNA

An electrochemical sensor was developed based on gold nanoparticles incorporated in mesoporous MFI zeolite for the determination of purine bases. Au nanoparticles (AuNPs) were incorporated into the mesoporous MFI zeolite (AuNPs/m‐MFI) by post‐grafting reaction. The composite materials were characterized by transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and electrochemical methods. Au nanoparticles with a size of 5‐20 nm are uniformly dispersed in the pores of mesoporous MFI zeolite. And the morphology of MFI zeolite can be perfectly kept after pore expansion and Au nanoparticles incorporation. The electrocatalytic oxidation of purine bases (guanine and adenine in DNA) is investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface‐confined Au nanoparticles provide the good catalytic activity for oxidation of purine bases. The simultaneous detection of guanine and adenine can be achieved at AuNPs/m‐MFI composites modified glassy carbon electrode (GCE). The electrochemical sensor based on AuNPs/m‐MFI exhibits wide linear range of 0.5–500 μM and 0.8–500 μM with detection limit of 0.25 and 0.29 μM for guanine and adenine, respectively. Moreover, the electrochemical sensor is applied to evaluation of guanine and adenine in herring sperm DNA samples with satisfactory results.     

Fabrication of DNA nanowires by orthogonal self-assembly and DNA intercalation on a Au patterned Si/SiO2 surface

A novel Ru complex bearing both an acridine group and anchoring phosphonate groups was immobilized on a surface in order to capture double-stranded DNAs (dsDNAs) from solution. At low surface coverage, the atomic force microscopy (AFM) image revealed the "molecular dot" morphology with the height of the Ru complex ( approximately 2.5 nm) on a mica surface, indicating that four phosphonate anchor groups keep the Ru complex in an upright orientation on the surface. Using a dynamic molecular combing method, the DNA capture efficiency of the Ru complex on a mica surface was examined in terms of the effects of the number of molecular dots and surface hydrophobicity. The immobilized surface could capture DNAs; however, the optimal number of molecular dots on the surface as well as the optimal pull-up speed exist to obtain the extended dsDNAs on the surface. Applying this optimal condition to a Au-patterned Si/SiO 2 (Au/SiO 2) surface, the Au electrode was selectively covered with the Ru complex by orthogonal self-assembly of 4-mercaptbutylphosphonic acid (MBPA), followed by the formation of a Zr (4+)-phosphonate layer and the Ru complex. At the same time, the remaining SiO 2 surface was covered with octylphosphonic acid (OPA) by self-assembly. The selective immobilization of the Ru complex only on the Au electrode was identified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging on the chemically modified Au/SiO 2 surface. The construction of DNA nanowires on the Au/SiO 2 patterned surface was accomplished by the molecular combing method of the selective immobilized Ru complex on Au electrodes. These interconnected nanowires between Au electrodes were used as a scaffold for the modification of Pd nanoparticles on the DNA. Furthermore, Cu metallization was achieved by electroless plating of Cu metal on a priming of Pd nanoparticles on the Pd-covered DNA nanowires. The resulting Cu nanowires showed a metallic behavior with relatively high resistance.