Formation Mechanism Of Gold Nanoparticles Research Articles

Investigation of the formation mechanism of gold nanoparticles in arsenian pyrite crystal structure of the Zarshuran deposit by advanced electronic technologies

Investigation of the formation mechanism of gold nanoparticles in arsenian pyrite crystal structure of the Zarshuran deposit by advanced electronic technologies

The Complexity of Microbial Metal Nanoparticle Synthesis: A Study of Candida parapsilosis ATCC 7330 mediated Gold Nanoparticles Formation

Understanding the biosynthetic mechanism of gold nanoparticle formation is the key to controlling the size, dispersity, and morphology of the nanoparticles. Reduction of gold (III) to gold (0) in cell-free extracts of Candida parapsilosis ATCC 7330 is not only enzymatic, as confirmed by experiments with heat denatured extracts. In addition to proteins, cellular reducing equivalents also contribute to the formation of gold nanoparticles in a concentration-dependent manner. Characterization of the bio-synthesized gold nanoparticles using X-ray photoelectron spectroscopy and elemental analysis revealed that nanoparticles are stabilized by proteins. The importance of protein three-dimensional structure in producing stable gold nanoparticles is also addressed. Making free thiol groups (–SH) unavailable by derivatizing them in protein extracts resulted in monodisperse gold nanoparticles implying that free –SH increase aggregation and emphasize this as a possible strategy to produce monodisperse gold nanoparticles in biological extracts which is otherwise difficult.

New insights into the formation mechanism of gold nanoparticles using dopamine as a reducing agent

Dopamine (DA), a simplified mimic of mussel proteins, can be employed as a reductant in the preparation of Au nanoparticles (AuNPs) due to its inherent catechol building block. The widely accepted mechanism of AuNP formation using DA as the reductant assumes that the reduction of Au(III) ions involves the two-electron oxidation of DA, where the corresponding phenol and phenolates serve as the reductive species to yield quinone. We herein report a novel insight into the mechanism of formation of AuNPs using DA as the reductant. We demonstrate that the synthesis of AuNPs requires the prior oxidation of the DA to form quinone units, which then catalyze the formation of semiquinones. These semiquinone radicals (SMQs) reduce the Au(III) ions to form the initial AuNPs, and further growth is then catalyzed by the first AuNPs, with nucleation occurring where the SMQs, phenols, and phenolates can serve as reductive species. In addition, DA oxidizes and polymerizes to form a polydopamine capping layer on the AuNPs. We therefore expect that the novel mechanism proposed herein may promote us to furthermore explore the production of noble metal NPs using other polyphenols.

COPT2, a plasma membrane located copper transporter, is involved in the uptake of Au in Arabidopsis

The mechanism of gold nanoparticle formation and genes involved in such processes, especially Au transport in plants are not understood. Previous reports pointed to the probable role of COPT2 in Au transport based on the transcript accumulation of COPT2 under Au exposure. Here, we provide evidence revealing the additional role of COPT2 for Au mobilization in yeast and Arabidopsis. The COPT2 transcripts significantly accumulated in the root of Arabidopsis under Au exposure. The expression of COPT2 restores Cu uptake ability in ctr1Δctr3Δ mutants and leads to Au sensitivity in yeast, which is comparable to Cu in growth kinetics experiments. The metal measurement data showed that the Au level was increased in COPT2, expressing yeast cells compared to vector transformed control. The copt2 mutant of Arabidopsis displayed a similar growth pattern to that of Col-0 under Au treatment. However, a notable phenotypic difference was noticed in three-week-old plants treated with and without Au. Consistent with yeast, Au uptake was reduced in the copt2 mutant of Arabidopsis. Together, these results clearly reveal the Au uptake capability of COPT2 in yeast and Arabidopsis. This is the first report showing the potential role of any transporter towards uptake and accumulation of Au in plants.

Formation Mechanism of Gold Nanoparticles Synthesized by Photoreduction in Aqueous Ethanol Solutions of Polymers Using In Situ Quick Scanning X-ray Absorption Fine Structure and Small-Angle X-ray Scattering

The photoreduction process of [AuCl4]− precursors in poly(N-vinyl-2-pyrrolidone) solution was investigated by utilizing a combination of in situ quick scanning X-ray absorption fine structure (QXAFS) and small-angle X-ray scattering (SAXS) measurements to elucidate the nucleation and subsequent aggregative particle growth of colloidal gold nanoparticles (Au NPs). The sequence of stages for the reduction–nucleation and association process (autocatalytic surface growth and aggregative particle growth) of Au atoms to generate Au NPs was observed during the photoreduction. QXAFS analysis revealed that the reduction of [AuCl2]− species to Au0 atoms is a slower step than that of [AuCl4]− to [AuCl2]−, and the reduction of [AuCl2]− to Au0 atoms and the association of Au0 atoms to produce Au nucleates concurrently proceeds during short-duration photoirradiation. A sigmoidal curve expressed by the solid-state kinetic model, specifically the Avrami-Erofe’ev model, was applicable to demonstrate the aggregative partic...

Investigation on the Mechanism of the Synthesis of Gold(I) Thiolate Complexes by NMR

In this article, we characterized the polymeric gold(I) thiolates that precipitated from the intermediate solutions during the synthesis process of gold nanoparticles (GNPs) by the Brust–Schiffrin two-phase method and investigated the formation mechanism of the polymeric gold(I) thiolates. The solution 1H NMR confirmed the complete reduction from Au(III) to Au(I) with the addition of the first two equivalents of thiols, while only the third and fourth equivalents of thiols were found to participate in forming gold(I) thiolates. Gold(I) thiolates, [Au(I)SR]n, precipitated from these solutions were further characterized by 1H solid-state NMR spectroscopy under fast magic angle spinning (MAS), Raman spectroscopy, and thermogravimetric analysis. Further quantitative studies revealed that the composition of [Au(I)SR]n could be controlled by changing the order of addition of the third and fourth equivalents of thiols. This work has great significance to better understand the mechanism of gold nanoparticle formation and thus to tailor the properties of the final products.

Facile and rapid thermo-regulated biomineralization of gold by pullulan and study of its thermodynamic parameters

A novel method for the production of gold nanoparticles (AuNPs) using pullulan as reducing and stabilizing agent has been developed. Quasi-spherical shaped AuNPs in the range of 50–100nm were produced at three different temperature regimes 80°C, 90°C and 100°C as characterized using UV–vis spectrophotometer, TEM and DLS. Study of reaction kinetics and thermodynamic parameters indicated that the reaction between pullulan and chloroauric acid for AuNPs formation followed first order reaction kinetics and higher temperature was favorable for the synthesis of smaller sized AuNPs. FT-IR data analyses, provided an insight towards the mechanism of gold nanoparticle formation which suggested that, the free CH2OH groups of pullulan molecule were oxidized to carboxylate ions resulted in formation of AuNPs whereas the basic skeletal structure of pullulan remained unaltered. This study may open up new avenues for synthesis of tailor made biogenic AuNPs with possible application in biomedical field.

Rapid synthesis of gold nanostructures with cyclic and linear ketones

Colloidal gold nanoparticles were synthesised in aqueous solution by reaction of chloroauric acid with a range of simple aliphatic cyclic (cyclopentanone, cyclohexanone, cycloheptanone and cyclohexanedione) and linear (acetone and 3-hexanone) ketone reagents, at room temperature. The rate of reaction and particle morphology was found to be controlled by the enol content and solubility of the ketone. Cyclohexanediones produced a variety of small 20 nm particles in under 5 minutes, or larger gold nanostars, depending on the ketone isomer. Cyclopentanone was shown to produce near monodisperse 20 nm particles after 13 hours, and cycloheptanone gave polydisperse particles, but in only 50 minutes. However the linear ketones, 3-hexanone and acetone, did not produce stable colloidal suspensions. The mechanism of gold nanoparticle formation via reaction of ketones with chloroauric acid is discussed.

Silica sacrificial layer-assisted in-plane incorporation of Au nanoparticles into mesoporous titania thin films through different reduction methods

This study focuses on the incorporation of gold nanoparticles (Au NPs) into our previously synthesized mesoporous titania thin films consisting of titania nanopillars and inverse mesospace (C. W. Wu, T. Ohsuna, M. Kuwabara and K. Kuroda, J. Am. Chem. Soc., 2006, 128, 4544-4545, denoted as MTTFs). Recently, mesoporous titania materials doped with noble metals such as gold have attracted considerable attention because noble metals can enhance the efficiency of mesoporous titania-based devices. In this research, we attempted to use four different reduction methods (i.e., thermal treatment, photo irradiation, liquid immersion, and vapor contacting) to introduce gold nanoparticles (Au NPs) into MTTFs. The synthesized Au@MTTFs were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We further systematically investigated the formation mechanism of gold nanoparticles on the external and internal surfaces of the MTTFs. With the assistance of a silica sacrificial layer, well-dispersed Au NPs with sizes of 4.1 nm were obtained inside the MTTF by photo irradiation. The synthesized Au@MTTF materials show great potential in various photo-electronic and photo-catalytic applications.

An in situ XAFS study—the formation mechanism of gold nanoparticles from X-ray-irradiated ionic liquid

An in situ X-ray absorption fine structure (XAFS) experiment has been performed to observe the evolution of gold nanoparticles in the ionic liquid [BMIM][AuCl4], by hard X-ray irradiation. The ionic liquid acts as both a reducing agent and a protective ligand. A synchrotron-based X-ray plays the role of the irradiation source, which induces the reduction of the gold species, as well as being a real time probe for XAFS measurements. From the extended X-ray absorption fine structure (EXAFS) fitting results for a series of spectra of gold L3-edge, it can be seen clearly that there is a single Au-Cl bond breaking process before the formation of Au-Au bonds, which is different from previous reports on the formation of Au nanoparticles by several chemical methods.

Influence of Single Use and Combination of Reductants on the Size, Morphology and Growth Steps of Gold Nanoparticles in Colloidal Mixture

A comprehensive investigation on the formation mechanism of gold nanoparticles (AuNPs) in colloidal mixture obtained from the reduction of chloroauric acid (HAuCl4) solution using a single reducing agent (sodium citrate; process-I), (tannic acid; process-II), and a combination of two reducing agents (sodium citrate plus tannic acid; process-III) is reported. The growth steps at different time intervals during synthesis of colloidal AuNPs were monitored in situ and ex situ using various methods for all the three processes. The measurement of changes in the surface plasmon band position of colloidal AuNPs, along with dynamic light scattering results gave important information for the first assessing of particle size, shape and distribution. Besides, the size and morphological changes at different stages during different processes were also analyzed by transmission electron microscopy. The final Au particles of processes-I & II exhibited different shapes (spherical and nanowires) with particle size and nano wire diameter of 12 nm and 17 nm, respectively. Nevertheless, combination of two reductants (process-III) surprisingly leads to drastically reduced size (ca. 3 nm) with spherical morphology compared to their parent solutions with either of single reducing agent. This result clearly indicates that the combination of reductants has a significant influence on the particle size, morphology and formation mechanism.

Facile synthesis of concentrated gold nanoparticles with low size-distribution in water: temperature and pH controls

The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

Influence of Monomer Feeding on a Fast Gold Nanoparticles Synthesis: Time-Resolved XANES and SAXS Experiments

A comprehensive study of the mechanism of gold nanoparticle formation has been conducted using third-generation synchrotrons. The particles were obained by reduction of AuCl(3) by BH(4)(-) in toluene. Gold oxidation state was monitored by X-ray absorption near edge spectroscopy (XANES), while the size and concentration of the nanoparticles were assessed by small-angle X-ray scattering (SAXS). A time-resolution of 100 ms has been achieved for a total formation time of a few seconds. The change with time of the total amount of Au(0) present in the solution is obtained by XANES. The change of the amount of Au(0) inside the nanoparticles is obtained from the SAXS signal. The comparison between these two quantities shows that a measurable amount of Au(0) exists transiently as monomers (or very small entities) in solution and this quantity is linked to an observed burst of nucleation of nanoparticles. The reduction kinetics is strongly influenced by the presence of ligands and a change in temperature. A model coupling the observed reduction kinetics and nucleation and growth laws is able to recover the final size and number densities of the explored experimental conditions.

Mechanism of Gold Nanoparticle Formation in the Classical Citrate Synthesis Method Derived from Coupled In Situ XANES and SAXS Evaluation

Although gold nanoparticles (GNP) are among the most intensely studied nanoscale materials, the actual mechanisms of GNP formation often remain unclear due to limited accessibility to in situ-derived time-resolved information about precursor conversion and particle size distribution. Overcoming such limitations, a method is presented that analyzes the formation of nanoparticles via in situ SAXS and XANES using synchrotron radiation. The method is applied to study the classical GNP synthesis route via the reduction of tetrachloroauric acid by trisodium citrate at different temperatures and reactant concentrations. A mechanism of nanoparticle formation is proposed comprising different steps of particle growth via both coalescence of nuclei and further monomer attachment. The coalescence behavior of small nuclei was identified as one essential factor in obtaining a narrow size distribution of formed particles.

Nucleation and Growth of Gold Nanoparticles Studied via in situ Small Angle X-ray Scattering at Millisecond Time Resolution

Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process ( approximately 2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV-vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formation. The first step is a rapid conversion of the ionic gold precursor into metallic gold nuclei, followed by particle growth via coalescence of smaller entities. Consequently it could be shown that the studied synthesis serves as a model system for growth driven only by coalescence processes.

Template- and micelle-free synthesis of rod-like gold nanoparticles with UVA irradiation

Rod-like gold nanoparticles can be formed from HAuCl4 aqueous solution with ultraviolet (UV) irradiation in the absence of templates, avoiding possible poisonous surfactant embedded into the surface of functional gold nanoparticles applied in biomedicine. The aspect ratio of nanorods ranges from 1.1 to 4.4 with the concentration of HAuCl4 0.2 mM, which can be verified by HRTEM images and the absorption spectrum. It is found that the nanocluster with several atoms occurs prior to the formation of nanorods, highly corresponding to its typical absorption spectrum. Tracing the evolution in absorption spectra of HAuCl4 aqueous solution, it can be concluded that the formation mechanism of gold nanoparticles in this process is different from that in the conventional inductive growth model, possibly in a growth pattern with imperfect oriented attachment (IOA) relevant to the colliding-and-growing.

Formation of gold nanoparticles in polymethylmethacrylate by UV irradiation

Gold–polymethylmethacrylate (PMMA) nanocomposites were fabricated with a photoreduction method using UV irradiation. The irradiated samples are compared with unirradiated ones to investigate the mechanism of gold nanoparticle formation and the effect of UV irradiation and polymer matrix on the morphology of the particles. The triangular gold nanoparticles were formed in polymer medium at a specific concentration of gold salt and UV exposure. The particle size decreased when the gold salt to polymer ratio was increased. The samples were analysed using UV–Vis spectroscopy, Fourier transform infrared spectrometry, atomic force microscopy, x-ray diffraction, small angle x-ray scattering and x-ray photoelectron spectroscopy. The interfacial interaction of Au nanoparticles and PMMA polymer has been discussed.

Formation of Gold Nanoparticles by Good’s Buffers

Abstract Gold nanoparticle formation was found from tetrachloroaurate(III) in the presence of Good’s Buffers, such as 2-morpholinoethanesulfonic acid (MES) and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES), which are used widely in laboratories for studies of analytical, inorganic, physical, and bio-chemistry as well as biology. The obtained gold nanoparticles were examined by Ultraviolet–Visible Spectroscopy (UV–vis), Dynamic Light Scattering (DLS) and Electrophoretic Light Scattering (ELS) in an aqueous system and by transmission electron microscopy (TEM) for particle morphologies. UV–vis spectra showed absorption maxima at ∼530 and ∼750 nm, depending on the buffer reagents and their concentration, pH, and ionic strength. The size and the surface zeta potential of the formed nanoparticles were 23 to 73 nm and −30 to −12 mV, respectively. The TEM pictures clearly indicated the formation of finely dispersed, chained, or aggregated gold nanoparticles, depending on the experimental conditions. The mechanism of gold nanoparticle formation was studied by the measurements of cyclic voltammetry (CV) and electron spin resonance (ESR). MES and HEPES showed a positive anodic peak at approximately +800 mV vs Ag/AgCl electrode, which indicated that these buffering agents have mild reducing ability. ESR results indicated the generation of nitrogen-centered cationic free radicals from these Good’s Buffers in the presence of Au(III), resulting in the formation of gold nanoparticles. A reaction mechanism is proposed.