On the formation of protected gold nanoparticles from AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> by the reduction using aromatic amines

Amines are used extensively as reductants and subsequent capping agents in the synthesis of metal nanoparticles, especially gold, due to its affinity to nitrogen. Taking 2-methyl aniline as an example, we show that metal reduction is followed by polymerization of the amine, while part of it covers the nanoparticle surface another fraction deposits in the solution. It is found that the oxidative polymerization of the amine goes in step with the formation of gold nanoparticles. The gold nanoparticles thus formed have a mean diameter of 20 nm. The polymerized amine encapsulates the gold nanoparticle forming a robust shell of about 5 nm thickness, making the gold core inert towards mineralizing agents such as chloroform, bromoform, sodium cyanide, benzylchloride, etc. which react with the naked gold nanoparticles. The deposited polymer is largely protonated, taking up protons from the medium during its formation. Similar results have been observed in the case of aniline also. The materials have been fully characterized by spectroscopy and microscopy.This revised version was published online in August 2005 with a corrected issue number.     

Paclitaxel-loaded KMnF3 nanoparticles for cancer imaging and therapy in vivo

Stabilized gold nanoparticles are attracting more and more the interest of the scientific community, and this is mostly due to their versatility. We present the synthesis and characterization of gold nanoparticles of a mean diameter of 5.6 ± 0.4 nm stabilized using a terminal alkyne derivative of pyrene, a fluorophore able to act as a spectrofluorimetric probe. This capping moiety, including a propargylic ester, was designed to present a good tendency to interact with the gold surface possibly forming carbenoid intermediates. Its behaviour has been compared with the one of a linear terminal alkyne, also derivatized with a pyrene moiety. The changes in the photophysical properties of pyrene unambiguously show the formation of gold nanoparticles only using the species able to perform a rearrangement, clearly indicating that this ability is crucial for binding on the nanoparticles, the rather poorly stabilizing terminal alkynes.     

Sonosynthesis of gold nanoparticles from a geranium leaf extract

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV–Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8–20 nm, with an average size of 12 ± 3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.     

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.     

Protein-assisted synthesis route of metal nanoparticles: exploration of key chemistry of the biomolecule

Abstract  

Essentially, biomolecule assisted synthesis of inorganic nanoparticles can be divided into two categories. One uses multi-domain protein cages (template) and other relies on the self-assembly of the biomolecules including small peptides, DNA, and denatured protein. Protein templated synthesis of various nanomaterials is relatively well understood as the cages of the biological macromolecules and their specific interaction with inorganic ions ultimately dictate the size and crystallinity of the nanomaterials. On the other hand formation of nanoparticles using protein in the cost of the native structural integrity for the self-assembly is not well understood till date. In the present work we report a protein-assisted synthesis route to prepare highly crystalline 3–5 nm gold nanoparticles, which relies systematic thermal denaturation of a number of proteins and protein mixture from Escherichia coli in absence of any reducing agent. By using UV–vis, circular dichroism spectroscopy, and high-resolution transmission electron microscopy we have explored details of the associated biochemistry of the proteins dictating kinetics, size, and crystallinity of the nanoparticles. The kinetics of nanoparticles formation in this route, which is sigmoidal in nature, has been modelled in a simple scheme of autocatalytic process. Interestingly, the protein-capped as prepared Au nanoparticles are found to serve as effective catalyst to activate the reduction of 4-nitrophenol in the presence of NaBH₄. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy revealing the efficient catalytic activity of the nanoparticles have been explained in terms of the Langmuir–Hinshelwood model. The methodology and the details of the protein chemistry presented here may find relevance in the protein-assisted synthesis of inorganic nanostructures in general.     

Effect of a thioalkane capping layer on the first hyperpolarizabilities of gold and silver nanoparticles

We have measured the first hyperpolarizabilities of thioalkane capped silver and gold metallic nanoparticles. The values found are β(AgC 12-10 nm) = (2.10 ± 0.23) × 10(-26) esu for 10 nm diameter silver nanoparticles and β(AuC 18-18 nm) = (3.37 ± 0.08) × 10(-26) esu for 18 nm diameter gold nanoparticles at the fundamental wavelength of 784 nm. By comparison to the corresponding values reported for citrate capped silver and gold metallic nanoparticles, after size corrections, decreases by factors of 4.3 and 6.5 respectively are observed. These decreases are tentatively attributed to the bonds formed between the gold and silver surface atoms and the sulfur atoms of the capping layer.     

Nanostructures of gold coated iron core-shell nanoparticles and the nanobands assembled under magnetic field

Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with a stable noble metal, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties, which possess the potential application in high density memory device by forming self-assembling nanoarrays. Gold-coated iron core-shell structure nanoparticles (Fe/Au) synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 1∼2 nm shell. Since the gold shell is not epitaxial growth related to the iron core, the morié pattern can be seen from the overlapping of iron core and gold shell. However, the gold shell lattice can be seen by changing the defocus of TEM. An energy dispersive X-ray spectrum (EDS) also shows the nanoparticles are air-stable. The magnetic measurement of the nanoparticles also proved successful synthesis of gold coated iron core-shell structure. The nanoparticles were then assembled under 0.5 T magnetic field and formed parallel nanobands with about 10 μm long. Assembling two dimensional ordered nanoarrays are still under going. Received 29 November 2000     

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.     

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.     

Facile synthesis and electrochemical properties of octahedral gold nanocrystals

High-yield octahedral gold nanocrystals of ~45 nm in size have been facilely synthesized by one-pot reduction of HAuCl₄ using formic acid in cetyltrimethylammonium bromide (CTAB) aqueous solution. The results showed that CTAB can promote the formation of single-crystalline nucleation and preferentially adsorb on the (111) planes of gold nanocrystals, resulting in the formation of octahedral gold nanocrystals. Formic acid acted as not only a mild reducing agent, but also could promote the formation of (111) facet. The octahedral gold nanocrystals exhibited similar cyclic voltammetry (CV) curves to single-crystal Au (111) electrode and excellent electrocatalytic activity for methanol oxidation. This synthetic strategy may open new route for facile synthesis of shape-controlled metal nanoparticles.     

Optimization of components in high-yield synthesis of block copolymer-mediated gold nanoparticles

The optimization to achieve stable and high-yield gold nanoparticles in block copolymer-mediated synthesis has been examined. Gold nanoparticles are synthesized using block copolymer P85 in gold salt HAuCl₄·3H₂O solution. This method usually has a very limited yield which does not simply increase with the increase in the gold salt concentration. We show that the yield can be enhanced by increasing the block copolymer concentration but is limited to the factor by which the concentration is increased. On the other hand, the presence of an additional reductant (trisodium citrate) in 1:1 molar ratio with gold salt enhances the yield by manyfold. In this case (with additional reductant), the stable and high-yield nanoparticles having size about 14 nm can be synthesized at very low block copolymer concentrations. These nanoparticles thus can be efficiently used for their application such as for adsorption of proteins.     

磁控溅射法制备金团簇纳米颗粒及性能表征

 采用磁控溅射法制备金团簇纳米颗粒，用透射电镜(TEM)、X射线衍射(XRD)、紫外可见光分光光度计(UV-Vis)和X射线光电子能谱(XPS)等分析手段对其表征，研究了金团簇纳米颗粒的形貌、颗粒度、结构、光吸收性质及物质成份。研究结果表明：制备的金团簇纳米颗粒呈球形，平均粒径在10 nm左右，粒径分布均匀，无团聚、氧化现象，颗粒的结构为面心立方。在519 nm处出现团簇颗粒的表面等离子共振吸收峰，测试得到Au(4f_7/2)和Au(4f_5/2)电子的结合能分别为83.3 eV和86.9 eV，并且没有出现金的氧化产物。     

Synthesis and characterization of spherical and narrow size distribution indium oxide nanoparticles

This work reports the synthesis of indium oxide nanoparticles and their thermal, structural, microstructural and optical characterization. The preparation method is based on a surfactant-free room temperature soft chemistry route. Spherical indium oxide nanoparticles (about 8 nm in diameter) were obtained after thermal treatment of gels at 400 °C for 2 h, as shown by X-ray diffraction experiments and nitrogen adsorption measurements. Transmission electron microscopy observations confirm the single-crystalline nature of the produced nanoparticles. The photoluminescence emission spectrum at room temperature shows a broad peak with onset at approximately 315 nm as a result of quantum size effect as revealed by small-angle X-ray scattering.     

Gold nanoparticle superlattice crystallization probed in situ

The nucleation and growth of three-dimensional superlattices of gold nanoparticles has been followed directly in situ by means of small angle x-ray scattering. These assemblies spontaneously form in a dilute solution providing the particles are large enough to generate a van der Waals driven attraction sufficient to counterbalance the thermal energy. The superlattices nucleate very soon after the birth of the individual particles and their growth kinetics is slower than predicted by a mechanism of simple diffusion of the nanoparticles towards the superlattices. The superlattices are first limited in size (170 nm in diameter) and have a globular shape with a low polydispersity. They present a fcc inner structure with nanoparticles being separated by a capping agent bilayer yielding a low gold internal volume fraction (phi SL = 0.33). In a second stage, these superlattices coalesce with time.     

Gold nanoparticles produced in a microalga

An efficient biological route to production of gold nanoparticles which allows the nanoparticles to be easily recovered remains elusive. Live cells of the green microalga Chlorella vulgaris were incubated with a solution of gold chloride and harvested by centrifugation. Nanoparticles inside intact cells were identified by transmission electron microscopy and confirmed to be metallic gold by synchrotron based X-ray powder diffraction and X-ray absorption spectroscopy. These intracellular gold nanoparticles were 40–60 nm in diameter. At a concentration of 1.4% Au in the alga, a better than 97% recovery of the gold from solution was achieved. A maximum of 4.2% Au in the alga was obtained. Exposure of C. vulgaris to solutions containing dissolved salts of palladium, ruthenium, and rhodium also resulted in the production of the corresponding nanoparticles within the cells. These were surmised to be also metallic, but were produced at a much lower intracellular concentration than achieved with gold. Iridium was apparently toxic to the alga. No nanoparticles were observed using platinum solutions. C. vulgaris provides a possible route to large scale production of gold nanoparticles.     

Pulsed-laser generation of gold nanoparticles with on-line surface plasmon resonance detection

Size of nanoparticles is an important parameter for their applications. The real-time monitoring is required for reliable and reproducible production of nanoparticles with controllable size. We present results of our research on development of the system for the online nanoparticle characterization during their production by a laser. The laser ablation chamber which allows measurements of surface plasmon resonance spectra during the nanoparticle generation process has been designed and fabricated. The online characterization system was tested by producing and modification of gold nanoparticles. Nanoparticles were generated by nanosecond-laser (wavelength 1064 nm) ablation of gold target in deionized water, and optimal conditions for the highest nanoparticle productivity were estimated. The mean diameter of nanoparticles was determined using their absorption spectra measured in the real-time during the ablation experiments and from the TEM images analysis, and it varied from 20 to 45 nm. The mismatch between nanoparticle diameters, estimated using these two methods, is due to the polydispersity of the generated nanoparticles. The further experiments of laser-induced modification of colloidal gold nanoparticles were carried out using second harmonic (wavelength 532 nm) of nanosecond Nd:YAG laser and alteration in nanoparticle size were acquired by the online measurement system.     

Optical manipulation of gold nanoparticles using an optical nanofiber

Gold nanoparticles are gaining increasing attention due to their biological and medical applications.In this letter,we experimentally demonstrate the optical manipulation of 250-nm-diameter gold nanoparticles along an optical nanofiber(550 nm in diameter) injected by an 808-nm laser light.The nanoparticles situated in the evanescent optical field are trapped by optical gradient force and move along the direction of light propagation due to optical scattering force.The velocities reach as high as 132 μm/s at an optical power of 80 mW.     

Spectra of resonance light scattering of gold nanoshells: Effects of polydispersity and limited electron free path

The effects of the polydispersity of the structure of gold nanoshells and of the limited electron free path in a thin metal layer on the spectra of resonance light scattering of a suspension of two-layer nanoparticles are studied theoretically and experimentally for the first time. It is shown theoretically that both factors lead to a broadening of the plasmon resonance in light scattering and to a change in its magnitude. To experimentally test the calculations, two samples of nanoshells based on gold and silicon dioxide (silica) were synthesized. Nanoshells of sample 1 have a diameter of the core of 90 nm and a broad thickness distribution of shells (with an average value of 30 nm), whereas nanoshells of sample 2 have a diameter of the core of 70 nm and a narrow thickness distribution of shells (with an average value of 12 nm). The core diameter, the shell thickness, and the polydispersity of the structure of nanoparticles are estimated by dynamic light scattering. It is shown that the simulation of the optical properties of nanoparticles with their parameters estimated from the dynamic light scattering data makes it possible to obtain good agreement between experimental and theoretical spectra of light scattering. For nanoshells of sample 1, the inhomogeneous broadening of the scattering spectrum is completely determined by the polydispersity; therefore, the bulk constants of gold can be used in simulation of the spectra of such nanoshells. The main mechanism of the broadening for nanoshells of sample 2 is connected with the limitation of the free path length of electrons, whereas the contribution from the thickness distribution of shells can be neglected.     

Synthesis of low-melting-point metallic nanoparticles with an ultrasonic nanoemulsion method

A one-step, economical nanoemulsion method has been introduced to synthesize low-melting-point metallic nanoparticles. This nanoemulsion technique exploits the extremely high shear rates generated by the ultrasonic agitation and the relatively large viscosity of the continuous phase - polyalphaolefin (PAO), to rupture the molten metal down to diameter below 100 nm. Field’s metal nanoparticles and Indium nanoparticles of respective average diameters of 15 nm and 30 nm have been obtained. The nanoparticles size and shape are determined by transmission electron microscopy (TEM). Their phase transition behavior is examined using a differential scanning calorimeter (DSC). It is found that these nanoparticles dispersed in PAO can undergo reversible, melting-freezing phase transition, and exhibit a relatively large hysteresis. The experimental results suggest that the nanoemulsion method is a viable route for mass production of low-melting nanoparticles.     

Room temperature synthesis of an optically and thermally responsive hybrid PNIPAM–gold nanoparticle

Composites of metal nanoparticles and environmentally sensitive polymers are useful as nanoactuators that can be triggered externally using light of a particular wavelength. We demonstrate a synthesis route that is easier than grafting techniques and allows for the in situ formation of individual gold nanoparticles encapsulated by an environmentally sensitive polymer, while also providing a strong interaction between the polymer and the metal particle. We present a one-pot, room-temperature synthesis route for gold metal nanoparticles that uses poly-N-isopropyl acrylamide as the capping and stabilizing agent and ascorbic acid as the reducing agent and achieves size control similar to the most common citric acid synthesis. We show that the composite can be precipitated reversibly by temperature or light using the non-radiative decay and conversion to heat of the surface plasmon resonance of the metal nanoparticle. The precipitation is induced by the collapse of the polymer cocoon surrounding each gold nanoparticle, as can be seen by surface plasmon spectroscopy. The experiments agree with theoretical models for the heat generation in a colloidal suspension that support fast switching with low laser power densities. The synthesized composite is a simple nanosized opto-thermal switch.