Synthesis of hydrophobic gold nanoclusters: growth mechanism study,luminescence property and catalytic application

One-pot synthesis of well dispersed, size-controlled gold nanoparticles with the average size of 10–15 nm and luminescent gold nanoclusters with average size of 1.7–2.0 nm were successfully achieved by thermal decomposition of gold organometallic precursor CH₃AuPPh₃ in the presence of thiol surfactants in o-xylene. Only difference between the preparations of two types of Au nanoparticles is the amount of thiol surfactant employed. The mechanistic study of formation of gold nanoparticles was carried out by analyzing the samples at different reaction time intervals and revealed that two-staged growth process was involved. The nanoclusters showed strong red emission with the maximum intensity at about 600 nm. The maximum room temperature photoluminescence quantum yield was measured as 1.2%. The catalytic ability of the Au nanoclusters to promote Suzuki–Miyaura coupling involving the C–C bond formation was also investigated.     

Fabrication of gold nanoparticles in water by laser ablation technique and their characterization

A colloidal solution of gold nanoparticles in deionized nanopure water was produced by laser ablation technique without the use of any chemical/surfactant. Spectral characterization and morphological studies of these nanoparticles were carried out by UV-Vis Spectroscopy and Scanning Electron Microscopy, respectively. A number of variables of the ablating laser pulse have been used to control the size of the fabricated nanoparticles. Excellent correlation between ablating laser pulse parameter and optical and morphological parameters of the gold colloids were obtained. The peak of the extinction spectra shows a monotonic blue shift for laser fluence of 410 J/cm² and above. Below this the extinction peak remains fairly constant in wavelength. Blue shifts of the extinction spectra were also observed with increasing re-ablation time of previously ablated gold colloids. Possible explanations of all these observations are discussed.     

Synthesis and characterization of gadolinium nanostructured materials with potential applications in magnetic resonance imaging,neutron-capture therapy and targeted drug delivery

Two Gadolinium nanostructured materials, Gd₂(OH)₅NO₃ nanoparticles and Gd(OH)₃ nanorods, were synthesized and extensively characterized by various techniques. In addition to the potential use of Gd₂(OH)₅NO₃ in magnetic resonance imaging (MRI) and Neutron-capture therapy (NCT) application, it could also be used in targeted drug delivery. An antibiotic (nalidixic acid), two amino acids (aspartic and glutamic acid), a fatty acid and a surfactant (SDS) were intercalated in the nanoparticles. The surface of the nanoparticles was modified with folic acid in order to be capable of targeted delivery to folate receptor expressing sites, such as tumor human cells.     

Cysteine Induced Chiral Morphology in Palladium Nanoparticle

New morphology of palladium nanoparticles is demonstrated by utilizing the interaction of amino acid and palladium metallic surface. Chiral cysteine molecules induce chiral spiral structure evolution. The resulting spiral palladium nanoparticles show rotational direction preference with respect to the handedness of the added cysteine molecule. The strong correlation of the resulting morphologies with surfactant and cysteine concentration exists for effective generation of chirality. Synthesized chiral palladium nanoparticles are around 100 nm sized cubic based nanoparticles with each face of the cube containing a spiral structure. Generation of nanoparticle morphology is studied through growth of time‐dependent morphology evolution with statistical analysis of spiral structure formation. The reported synthesis method can provide a new route to nanomaterial design for enantioselective catalysis and sensing.     

Efficient and Rapid Synthesis of Radioactive Gold Nanoparticles by Dielectric Barrier Discharge

A compact bench‐top system based on a dielectric barrier plasma discharge (DBD), enables the rapid, automatable, and continuous‐flow synthesis of gold nanoparticles (AuNPs) and radioactive gold nanoparticles (¹⁹⁸AuNPs). AuNPs are used as radiosensitizers in oncology, and ¹⁹⁸AuNPs (half‐life: 2.7 d) have been suggested as potential cancer brachytherapy sources. Plasma applied at the surface of a liquid containing gold ions (AuCl₄^?) and dextran induces the production of AuNPs directly in water. This synthesis is monitored in real time by UV–visible spectrometry: the change of absorbance of the solution provides new insights on the growth dynamics of AuNPs by plasma synthesis. By balancing gold ions and surfactant molecules, particles with a diameter lying in the optimal range for radiosensitizing applications (28 ± 9 nm) are produced. The method yields a reduction of more than 99% of the gold ions within only 30 min of plasma treatment. A postsynthesis ripening of the AuNPs is revealed, monitored by UV–visible spectrometry, and quantified within the first few hours following plasma treatment. Radioactive ¹⁹⁸AuNPs are also produced by DBD synthesis and characterized by electron microscopy and single‐photon emission computed tomography imaging. The results confirm the efficiency of DBD reactors for AuNPs synthesis in oncology applications.     

Synthesis of ZnO nanoparticles using surfactant free in-air and microwave method

Zinc oxide nanoparticles have been successfully prepared by a facile route involving the reaction of zinc sulphate heptahydrate and sodium hydroxide through drop-by-drop mixing synthesis-IA, instant mixing synthesis-IA and under the influence of microwave radiations. The synthesis under different reaction conditions played an important role and led to the formation of zinc oxide nanoparticles of different size and shapes. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The concentration dependent antimicrobial activity of synthesized ZnO nanoparticles was carried out. The photocatalytic activity was evaluated using the photodegradation of methylene blue (MB) dye under UV irradiation. Further, the optical properties of as-prepared ZnO nanoparticles were investigated by UV-vis spectrophotometry. The absence of surfactant led to a simple, cheap and fast method of synthesis of zinc oxide nanoparticles.     

Preparation of surfactant-stabilized gold nanoparticle–peptide nucleic acid conjugates

A simple, two-step method of producing stable and functional peptide nucleic acid (PNA)-conjugated gold nanoparticles using a surfactant stabilization step is presented. PNA are DNA analogs with superior chemical stability and target discrimination, but their use in metallic nanoparticle systems has been limited by the difficulty of producing stable colloids of nanoparticle–PNA conjugates. In this work, the nonionic surfactant Tween 20 (polyoxyethylene (20) sorbitan monolaurate) was used to sterically shield gold surfaces prior to the addition of thiolated PNA, producing conjugates which remain dispersed in solution and retain the ability to hybridize to complementary nucleic acid sequences. The conjugates were characterized using transmission electron microscopy, dynamic light scattering, and UV–visible absorbance spectroscopy. PNA attachment to gold nanoparticles was confirmed with an enzyme-linked immunoassay, while the ability of nanoparticle-bound PNA to hybridize to its complement was demonstrated using labeled DNA.     

Injection of synthesized FePt nanoparticles in hole-patterns for bit patterned media

FePt nanoparticles of uniform sizes, compositions, and crystal structures can be obtained by chemical synthesis. Additionally, the nanoparticles can be well dispersed by the adsorption of a surfactant on the nanoparticle surface. Previously, the immobilization of FePt nanoparticles on a thermal oxide Si substrate was carried out by chemical synthesis, utilizing the Pt-S bonding between the -SH functional group in (3-mercaptopropyl)trimethoxysilane, MPTMS and Pt in FePt nanoparticles. However, controlling FePt nanoparticle arrays by this synthesis method was very difficult. In the present study, we attempted to control the distortion of the arrangement of FePt nanoparticles using an MPTMS layer modified with a silane coupling reaction and a geometrical structure prepared by ultraviolet nanoimprint lithography (UV-NIL). In this study, the hole-patterns used for the geometrical structure on Si(1 0 0) were 200 nm wide, 40 nm deep, and had a 500 nm pitch. The 5.6 nm FePt nanoparticles were used to coat the hole-patterns by using a picoliter pipette. An XHR-SEM image clearly revealed that the FePt nanoparticles were successfully arranged as a single layer with an average pitch of 10.0 nm by Pt-S bonding in the hole-patterns on Si(1 0 0).     

Effects of synthesis variables on the magnetic properties of CoFe2O4 nanoparticles

Cobalt ferrite nanoparticles (CoFe₂O₄) have been synthesized using precipitation in water solution with polyethylene glycol as surfactant. Influence of various synthesis variables included pH, reaction time and annealing temperature on the magnetic properties and particle sizes has also been studied. Structural identification of the samples was carried out using Thermogravimetric and Differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, High resolution transmission electron microscopy. Vibrating sample magnetometer was used for the magnetic investigation of the samples. Magnetic properties of nanoparticles show strong dependence on the particle size. The magnetic properties increase with pH of the precipitating medium and annealing temperature while the coercivity goes through a maximum, peaking at around 25 nm.     

憎水性金属纳米粒子及其LB膜的制备与光谱表征

用油酸钠和十四烷基硫醇作为稳定剂,制备了高度单分散的疏水性银和金纳米溶胶。考察了单粒子层的π－Ａ曲线并建造了纳米粒子的ＬＢ膜。通过紫外可见光谱讨论了纳米粒子的分散状态,由红外光谱结果讨论了纳米粒子表面有机吸附层的状态。     

Transforming single domain magnetic CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles from hydrophobic to hydrophilic by novel mechanochemical ligand exchange

Single-phase uniform-sized (~9 nm) cobalt ferrite (CFO) nanoparticles have been synthesized by hydrothermal synthesis using oleic acid as a surfactant. The as-synthesized oleic acid-coated CFO (OA-CFO) nanoparticles were well dispersible in nonpolar solvents but not dispersible in water. The OA-CFO nanoparticles have been successfully transformed to highly water-dispersible citric acid-coated CFO (CA-CFO) nanoparticles using a novel single-step ligand exchange process by mechanochemical milling, in which small chain citric acid molecules replace the original large chain oleic acid molecules available on CFO nanoparticles. The OA-CFO nanoparticle’s hexane solution and CA-CFO nanoparticle’s water solution remain stable even after 6 months and show no agglomeration and their dispersion stability was confirmed by zeta-potential measurements. The contact angle measurement shows that OA-CFO nanoparticles are hydrophobic whereas CA-CFO nanoparticles are superhydrophilic in nature. The potentiality of as-synthesized OA-CFO and mechanochemically transformed CA-CFO nanoparticles for the demulsification of highly stabilized water-in-oil and oil-in-water emulsions has been demonstrated.     

桑色素修饰金纳米粒子自组装膜的制备及其性能研究

采用水相硅烷化方法,将γ-氨基丙基三乙氧基硅烷[H₂N(CH₂)₃Si(OC₂H₅)₃](APES)组装在石英表面,在基底表面修饰上氨基为末端的单层膜,并进一步在这种功能化的单层膜基底上组装金纳米粒子得到金纳米粒子/APES/石英的纳米复合结构。以制备的金纳米粒子自组装膜修饰石英为基底及DL-半胱胺酸为中介,利用桑色素(Morin)和DL-半胱胺酸的化学吸附作用,将桑色素间接组装在金纳米粒子自组装膜修饰石英基底表面,所构建的桑色素修饰金纳米粒子自组装膜对三苯基锡有灵敏的荧光识别作用。文章着重研究了桑色素修饰金纳米粒子自组装膜的制备以及组装条件对其荧光行为的影响,探讨了膜的响应特性及响应机理。     

Tuning poly(p-phenylene) nano-size for enhancing electrical conductivity based on surfactant templates and doping

Nanoparticles play a vital role in the material property improvement. For conductive polymers, nanoparticles have been known to affect various electrical properties. This work reports the size-controlled synthesis of poly(p-phenylene) (PPP) nanoparticles using benzene, AlCl₃, and CuCl₂ as a monomer, catalyst, and oxidant respectively, incorporated with a surfactant template and subsequently doped with various doping agents to increase the electrical conductivity. The effects of surfactant types namely Span65, Tween80, and TritonX100 and surfactant concentrations were investigated. The PPP structure was confirmed by NMR, FT-IR, and XPS techniques. SEM images showed different undoped-PPP (uPPP) morphologies: irregular shape, coral reef shape, spherical shape, and worm-like shape with the particle sizes between ∼30 and ∼120 nm not previously reported. The electrical conductivity of the uPPP with a surfactant was higher than that without a surfactant due to the smaller particle size. From the doping, the electrical conductivity of the doped-PPP (dPPP) increased with the doping agent to monomer mole ratio up to 50:1. The dPPP doped with HClO₄ (dPPP/HClO₄) at the doping agent to monomer mole ratio of 50:1 exhibited the highest electrical conductivity of 74.34 S cm⁻¹ along with the long term stability in air.     

One-pot synthesis of gold/poly(3,4-ethylendioxythiophene) nanocomposite

In this paper, we report the preparation of highly stable gold nanoparticles/poly(3,4-ethylendioxythiophene) nanocomposites by a one-pot chemical route in aqueous medium without surfactants to increase the solubility of the monomer (3,4-ethylendioxythiophene, EDOT) or to stabilize gold nanoparticles (Au NPs). The generation of the nanocomposite was followed by UV–Visible transmission spectroscopy combined with multivariate curve resolution alternating least squares analysis to deconvolute the individual spectra of the different species generated in the synthesis: oligomers, polymer and gold nanoparticles. The plasmon band observed at 530 nm during the synthesis step indicates the generation of gold nanoparticles. The influence of monomer and metal precursor concentration and their concentration ratios on Au NP size were analyzed. The electrochromic properties of the composite were investigated by UV–Visible absorption spectroelectrochemistry, being mainly related to polymer oxidation and reduction. The main difference observed is the hypsochromic shift of the polymer spectra due to the gold nanoparticles inside the polymer. Multicyclic spectroelectrochemical experiments evidence a high stability and adhesion of the nanocomposite.     

Controllable synthesis of PbI2 nanocrystals via a surfactant-assisted hydrothermal route

PbI₂ nanostructures were successfully prepared via a surfactant-assisted hydrothermal method at a low temperature of 100°C for 8 h. Polyvinyl pyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB) were used as surfactants. The resulting products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis spectroscopy. It was found that the formation of PbI₂ nanostructures with various morphologies could be well controlled by the adjustment of the pH of the synthesis solution, selection of suitable surfactant, and the amount of the desired surfactant. UV–vis absorption results showed an apparent shift of the band gap energy of the PbI₂ nanoparticles relative to that of the bulk.     

Direct monitoring of gold nanorod growth

The seed-mediated growth of gold nanorods is shown to be strongly dependent on the reaction time and chemical environment of the reaction solution. The versatile seed-mediated approach in aqueous surfactant solutions has been used in this study for the synthesis of gold nanorods. Changes in the aspect ratio of gold nanorods were reflected in shifts of the plasmon resonance peaks and were monitored using UV-Visible absorption spectroscopy (UV-Vis) to follow the different stages of gold nanorod formation as a function of time and varying amounts of silver ion. Unlike the use of strong reducing agents to make spherical gold nanoparticles, the growth of gold nanorods requires weak reducing conditions, leading to an unknown degree of gold reduction. Therefore, cyclic voltammetry was used to electrochemically interrogate the entire reaction from gold seed to gold nanorod as a function of time. Data obtained revealed that time-dependent gold species are involved in gold nanorod formation.     

Preparation and bactericide activity of gallic acid stabilized gold nanoparticles

In this work, gold nanoparticles with three different sizes (13.7, 39.4, and 76.7 nm) were prepared using a simple aqueous method with gallic acid as the reducing and stabilizing agent, the different sizes were obtained varying some experimental parameters as the pH of the reaction and the amount of the gallic acid. The prepared nanoparticles were characterized using X-ray diffraction, transmission electron microscopy, dynamic light scattering, and UV–Vis spectroscopy. Samples were identified as elemental gold and present spherical morphology, a narrow size distribution and good stabilization according to TEM and DLS results. The antibacterial activity of this gallic acid stabilized gold nanoparticles against S. mutans (the etiologic agent of dental caries) was assessed using a microdilution method obtaining a minimum inhibitory concentration of 12.31, 12.31, and 49.25 μg/mL for 13.7, 39.4, and 76.7 nm gold nanoparticles, respectively. The antibacterial assay showed that gold nanoparticles prepared in this work present a bactericide activity by a synergistic action with gallic acid. The MIC found for this nanoparticles are much lower than those reported for mixtures of gold nanoparticles and antibiotics.     

Fabrication of a nanostructured gold-polymer composite material

A facile synthesis route is described for the preparation of a poly-(o-aminophenol)-gold nanoparticle composite material by polymerization of o-aminophenol (AP) monomer using HAuCl₄ as the oxidant. The synthesis was carried out in a methanol medium so that it could serve a dual solvent role, a solvent for both the AP and the water solution of HAuCl₄. It was found that oxidative polymerization of AP leads to the formation of poly-AP with a diameter of 50±10nm, while the reduction of AuCl₄ ^- results in the formation of gold nanoparticles (∼ 2nm). The gold nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer composite material. The resultant composite material was characterized by means of different techniques, such as UV-vis, IR and Raman spectroscopy, which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the composite material.     

Polymerizable Ligands as Stabilizers for Nanoparticles

Monomers bearing functional groups that can get chemisorbed on nanoparticles to form polymerizable monolayers have emerged as an interesting class of stabilizer ligands for various nanoparticles. High‐surface coverage, their ability to modify the properties of underlying nanoparticles, capability to form polymers of different molecular weights and possibility to make structural modifications make them attractive for their use as stabilizer ligands for nanoparticles. Both in situ and post‐synthesis grafting methods for attaching polymerizable ligands to nanoparticles are frequently used. The advantage of grafting polymerizable stabilizer on the surface of nanoparticles is that initially the polymerizable molecule acts as a proper stabilizer for the nanoparticles and later their surface polymerization or co‐polymerization with another suitable monomer can be carried out to generate the desired polymer scaffold around the nanoparticles, which ensures the increased stability of the resulting core‐polymerized shell nanoparticles. This review discusses interesting reports from recent literature on grafting of polymerizable ligands and their polymerization on gold, silver, silica, and iron oxide nanoparticles.     

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10^?7 cm²/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10^?1 cm/W.