Synthesis Of Au Nanoparticles Research Articles

Size-controlled synthesis of Au nanoparticles and nanowires and their application as SERS substrates

Different alkylamine-capped Au nanoparticles (NPs) and nanowires (NWs) have been successfully prepared through a facile one-pot solution growth method. Alkylamines serve as reducing agents and stabilizers in the synthetic process. As the chain length of alkylamines has an effect on the diffusion rate of monomers, the sizes of NPs and the diameters of NWs can be adjusted by adding different alkylamines in the synthetic process. Surface-enhanced Raman scattering (SERS) spectra of rhodamine 6G (Rh 6G) are obtained on the Au NPs and NWs modified substrates, indicating that the as-synthesized Au nanostructures have great potential for high sensitive optical detection application.

Strategy of fabricating enriched gold nanoparticles based on electrochemical methods

In this work, we report a new and clean electrochemical pathway to prepare enriched gold nanoparticles in aqueous solutions via the aid of chitosan without addition of any other stabilizer and reductant. First, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1N NaCl and 1g/L chitosan from −0.28 to +1.22V vs Ag/AgCl at 500mV/s with 500 scans. Then the Au working electrode was immediately replaced by a Pt electrode, and a cathodic overpotential of 0.6V from the open circuit potential (OCP) of ca. 0.84V vs Ag/AgCl was applied under sonification to synthesize Au nanoparticles. Experimental results indicate the concentration and the particle sizes of prepared Au nanoparticles are ca. 50ppm and 10nm in diameter, respectively. No aggregation of Au nanoparticles is observed in an ambient atmosphere for at least 3months.

Synthesis of Au nanoparticles at the surface and embedded in carbonaceous matrix by 150 keV Ar ion irradiation

We report on synthesis of spherical Au nanoparticles at the surface and embedded in carbonaceous matrix by 150 keV Ar ion irradiation of thin Au film on polyethyleneterepthlate (PET). The pristine and irradiated samples are characterized by Rutherford backscattering spectrometry (RBS), atomic force microscopy, scanning electron microscopy and transmission electron microscopy (TEM) techniques. RBS spectra reveal the sputtering of Au film and interface mixing, increasing with increasing fluence. Surface morphology shows that at the fluence of 5 × 1015 ions cm−2, dewetting of thin Au film begins and partially connected nanostructures are formed whereas, at the higher fluence of 5 × 1016 ions cm−2, isolated spherical Au nanoparticles (45 ± 20 nm) are formed at the surface. Cross-sectional TEM observations also evidence the Au nanoparticles at the surface and mixed metal–polymer region indicating the formation of nanocomposites with small Au nanoparticles. The results are explained by the crater formation, sputtering followed by dewetting of the thin Au film and interdiffusion at the interface, through molten zones due to thermal spike induced by Ar ions.

Protein Films of Bovine Serum Albumen Conjugated Gold Nanoparticles: A Synthetic Route from Bioconjugated Nanoparticles to Biodegradable Protein Films

Bovine serum albumen (BSA) conjugated gold (Au) nanoparticles (NPs) were directly synthesized by using BSA as a weak reducing agent against HAuCl4 in aqueous phase. A systematic variation in Au/BSA mole ratio showed a dramatic change in the size and shape of NPs which was very much dependent on the physical state of BSA. The nature of both colloidal NPs (due to surface plasmon resonance) and BSA (due to tryptophan residues) was monitored simultaneously by UV−visible measurements during the course of the reaction. A systematic variation in the reaction temperature from 20 to 70 °C demonstrated a clear denaturation process of BSA and how it influenced the synthesis of Au NPs. A predominantly native state of BSA that existed up to 40 °C proved to be a very mild reducing agent to convert Au(III) into Au(0). However, the reducing potential increased with unfolding of BSA beyond 40 °C and became maximum in the denaturation temperature range (i.e., 52−58 °C). Unfolded BSA conjugated NPs thus produced then starte...

Conductive Properties of Photoluminescent Au/Ps-b-PEO Inorganic/Organic Hybrids Containing Nematic Liquid Crystals

Novel inorganic/organic materials based on poly(styrene-b-ethylene oxide) block copolymers (PS-b-PEO) modified with synthesized Au nanoparticles and low molecular weight liquid crystals, 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC), have been investigated. The designed materials show a good dispersion of synthesized Au nanoparticles in one block of PS-b-PEO block copolymers. The conductive properties of the designed materials were measured using tunneling atomic force microscopy (TUNA). Au nanoparticles maintain conductive properties in investigated inorganic/organic materials. Simultaneously, the addition of even small amounts of nematic HOBC liquid crystals multiplied the TUNA-current passing throughout the investigated ternary systems. Moreover, the Au-(HOBC/PS-b-PEO) systems pose photoluminescent behavior of the low molecular HOBC liquid crystals allowing the design of nanostructured multiphase materials with the conductive properties of Au nanoparticles multiplied by HOBC and the photoluminescent prop...

Green synthesis of phytochemical-stabilized Au nanoparticles under ambient conditions and their biocompatibility and antioxidative activity

Green chemical synthesis of Au nanoparticles (NPs) has been of great interest because of its potential biomedical applications. In this study, we successfully produced phytochemical-induced Au NPs cofunctionalized with gallic acid, protocatechuic acid, and isoflavone. They have a strong antioxidant effect and serve as effective reducing agents, inducing the immediate passivation of Au NPs. The properties of these green chemical Au NPs were characterized by TEM, UV/Vis and FT-IR spectroscopy, and ζ-potential measurements, and the Au NPs exhibited excellent homogeneity with an average diameter of 20 nm and high dispersity at all pH ranges, with long-term stability as well as excellent cytocompatibility. Molecular dynamics (MD) simulations were also carried out in order to reveal the surface stability of the Au NPs. The computational results indicate that there are strong interactions between the phytochemicals and Au NPs, especially in the Au/protocatechuic acid–isoflavone model. Phytochemical-stabilized Au NPs allowed about 40% H2O2 to be removed at an NP concentration of 50 μg mL−1; this removal rate is the same as that achieved by 3000 units per mg catalase. Therefore, this novel synthesis route for Au NPs using phytochemical reducing agents may be effectively exploited for nonthermal-assisted reactions and one-pot processes of biological applications.

Facile green synthesis of gold nanoparticles with gum arabic as a stabilizing agent and reducing agent

A facile, completely green, and cheap route for the synthesis of Au nanoparticles at 25–75° has been developed by using only hydrogen tetrachloroaurate as the precursor and gum arabic (GA) simultaneously as a reducing agent and a stabilizing agent. No extra reagents are needed. From the analyses of UV/VIS absorption spectra, TEM, HRTEM, SAED, and XRD patterns, the formation of Au nanoparticles with a fcc structure was recognized. The synthesis reaction was usually finished in 2–4 h. Increasing the reaction temperature increased the formation rate but had no significant effect on the optical property and size of Au nanoparticles. With increasing Au(III) ion concentration or GA concentration, the mean diameter of Au nanoparticles slightly increased. Also, the particle size distribution became broader at higher Au(III) ion concentration or lower GA concentration due to the insufficient protection. Although raising the GA concentration was helpful to reduce Au(III) ions completely and stabilize the Au nanoparticles, too high GA concentration was not suitable for the stabilization of Au nanoparticles because the increased intermolecular force of GA might hinder the dispersion of Au nanoparticles. Furthermore, the resultant Au nanoparticles were found to remain highly stable in the NaCl solution.

Controlled Growth of Sub-10 nm Gold Nanoparticles Using Carbon Monoxide Reductant

There is a need to develop aqueous-phase synthesis methods of sub-10-nm Au nanoparticles (NPs), given their many exciting possibilities in catalysis, sensing, biomedical, and other water-based applications. Synthesizing Au NPs by reducing Au salt onto preformed NPs as seeds is a useful approach because final particle size can be finely predicted and controlled, though few studies have reported successful synthesis of Au NPs in the 1 and 10 nm size range. Here we report that water-suspended Au particles with a diameter ∼2.8 nm can be grown as large as ∼12 nm with sub-nanometer control, as verified through detailed ultraviolet−visible spectroscopy, small-angle X-ray scattering, and transmission electron microscopy measurements. With carbon monoxide as the reducing agent, this seeded-growth method results in colloidally stable Au sols. The reaction mechanism most likely involves the catalyzed oxidation of CO into CO2 accompanied by electron transfer to the gold hydroxide-chloride ionic species through the growing particle.

Biomineralization of Gold Nanoparticles by Lysozyme and Cytochrome c and Their Applications in Protein Film Formation

Lysozyme (Lys) and cytochrome c (Cyc,c) proteins were used as mild reducing and stabilizing agents to synthesize gold nanoparticles (NPs) at precisely 40 and 80 degrees C. All reactions were monitored simultaneously by UV-visible measurements to determine changes in the nature of the protein during the course of reaction. The synthesis of Au NPs caused the simultaneous denaturation of protein due to the formation of bioconjugate NPs, and the denaturation temperature decreased with the number of NPs. Lys entrapped NPs in a typical gel state, and Cyc,c carried them on well-defined micelles at 80 degrees C or in the form of long fibrils or strands at 40 degrees C. The shape, size, and arrangement of bioconjugate NPs were characterized by atomic force microscopy and transmission electron microscopy measurements. Purified bioconjugate NPs were further used in zein protein film formation. The resulting films were characterized by photophysical and mechanical measurements. The induction of bioconjugate NPs made protein films isotropic and relatively more brittle (with a greater effect for Cyc,c than for Lys conjugate NPs) than in their absence and was considered to be well suited for biomedical applications.

Enantioselective Separation on Chiral Au Nanoparticles

The surfaces of chemically synthesized Au nanoparticles have been modified with d- or l-cysteine to render them chiral and enantioselective for adsorption of chiral molecules. Their enantioselective interaction with chiral compounds has been probed by optical rotation measurements during exposure to enantiomerically pure and racemic propylene oxide. The ability of optical rotation to detect enantiospecific adsorption arises from the fact that the specific rotation of polarized light by (R)- and (S)-propylene oxide is enhanced by interaction with Au nanoparticles. This effect is related to previous observations of enhanced circular dichroism by Au nanoparticles modified by chiral adsorbates. More importantly, chiral Au nanoparticles modified with either d- or l-cysteine selectively adsorb one enantiomer of propylene oxide from a solution of racemic propylene oxide, thus leaving an enantiomeric excess in the solution phase. Au nanoparticles modified with l-cysteine (d-cysteine) selectively adsorb the (R)-propylene oxide ((S)-propylene oxide). A simple model has been developed that allows extraction of the enantiospecific equilibrium constants for (R)- and (S)-propylene oxide adsorption on the chiral Au nanoparticles.

Hydroxylated Dendrimer-Stabilized Gold and Silver Nanoparticles: Spontaneous Formation, Characterization, and Surface Properties

We present a general route to the facile and spontaneous synthesis of gold (Au) and silver (Ag) nanoparticles (NPs) through the use of hydroxylated poly(amidoamine) (PAMAM) dendrimers as both stabilizers and reducing agents. The formation of Au NPs can be achieved by simply mixing the generation 4 (G4) and 5 (G5) glycidol-modified PAMAM dendrimers with HAuCl4 in either methanol or water at room temperature. The size of the formed Au NPs can be varied through the change of dendrimer generations and reaction solvents. We also show that 1,2-epoxyhexane-modified G4 PAMAM dendrimers can be used as both stabilizers and reducing agents to form Au NPs, providing a useful approach to tuning the surface hydrophilicity of Au NPs. Furthermore, using the same strategy of spontaneous formation of Au NPs, Ag NPs can be readily formed through the use of glycidol hydroxyl-terminated G5 PAMAM dendrimers as both stabilizers and reducing agents. The facile synthesis of Au and Ag NPs using hydroxylated PAMAM dendrimers may offer many opportunities for their uses in a variety of applications. Keywords: Dendrimers, Gold nanoparticles, Silver nanoparticles, Hydroxylation, Stabilization

Droplet microfluidic preparation of au nanoparticles-coated chitosan microbeads for flow-through surface-enhanced Raman scattering detection

An integrated microfluidic device was fabricated to enable on-chip droplet forming, trapping, fusing, shrinking, reaction and producing functional microbeads for a flow-through single bead-based molecule detection. Dielectrophoresis (DEP) force was used to transport target polymer droplets into different predefined microwells, where the droplets were fused through electrocoalescence to form a new one with a desired diameter. In a continuous water loss process with water diffusion to oil phase, the polymer droplet was shrunken and solidified to form a polymer microbead. For a demonstration, Au nanoparticles-coated chitosan microbeads were in situ fabricated through droplet trapping, fusion and shrinking, followed by synthesis of Au nanoparticles on the microbead surface via a photoreduction process. The produced Au nanoparticle/chitosan microbead embedded in the microwell resulted in a highly sensitive, flow-through surface-enhanced Raman scattering (SERS) detection of Rhodamine 6G (R6G). This work successfully demonstrates an integrated droplet based lab-on-a chip and its application to fabricate an extremely high-throughput single bead based detection platform.

Controlling the size distribution of embedded Au nanoparticles using ion irradiation

Samples composted of chemically synthesized Au nanoparticles (NPs) (16.0±2.0 nm) embedded within a planar silica film are used as model system to investigate the evolution of a second phase under irradiation when the temperature and the ion stopping power are changed. Samples are irradiated with 4 MeV Au2+ ions and 4 MeV Br2+ ions for temperature ranging from 30 °C up to 800 °C and for fluences up to 8×1016 cm−2. We show that at room temperature the complete dissolution of the NPs leads to the formation of smaller precipitates with a narrower size distribution, i.e., 2.0±0.3 nm. However, when the temperature is increased and/or the nuclear stopping power is decreased, a reduction in the dissolution rate was observed. This leads to the formation of a bimodal size distribution. Finally, the evolution of the density of the precipitates with the temperature is discussed in term of the thermal stability of the irradiation-induced defects within the silica matrix.

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO2 nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO2 NPs. The multi-step process involves synthesis of pure Au and SnO2 NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO2 colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO2 NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO2 nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO2 between gold and tin oxide and formation of soldered nanocomposite.

Bioanalytical Applications of Au Nanoparticles

Nanoscale Au particles are received with significant interest in the recent years owing to their unique properties, which originate from the quantum scale dimension. Although colloidal Au has been known since ancient times for the decoration of glasses and for its curative powers, the technological importance has been understood only in the last two decades. The fascinating optical and electronic properties of the Au nanoparticles made them an excellent candidate in the development of nanoscale devices. Significant amount of research has been devoted to explore the technological application of these tiny particles. Various biosensing devices, catalytic interfaces and bioanalytical methodologies based on Au nanoparticles have been developed in the last two decades for different applications. Au nanoparticles are considered to be the key building blocks in the emerging nanoscale energy and sensing devices of 21(st) century. In this review, we highlight some of the recent patents and related literature on the bioanalytical applications of Au nanoparticles. A brief outline on the synthesis of Au nanoparticles of various size and shape and a detailed account of their potential utilization in the development of optical and electrochemical sensors/biosensors and analytical methods for drug delivery are discussed.

Electrocatalysis of Oxygen Reduction on Au Nanoparticles

The Oxygen Reduction Reaction (ORR) on synthesized Au nanoparticles was investigated. The reduction of AuCl3 with NaBH4 in THF forms highly crystalline Au particles with a face-centered cubic structure and approximate size of ~5nm. From RDE measurements the kinetic parameters were obtained, i.e. Tafel slope of -0.110 Vdec-1 and charge transfer coefficient, a =0.54. The Nyquist and Bode spectra of Au nanoparticles for E > 0.38 V vs NHE show one loop which may be associated to the reduction process of O2 to generate H2O2. The impedance spectra for E<0.38 V show a second time constant, which may be associated to a second process, ie. the reduction of H2O2 to H2O.

Halide ion controlled shape dependent gold nanoparticle synthesis with tryptophan as reducing agent: Enhanced fluorescent properties and white light emission

We report the synthesis of Au nanoparticles in presence of two surfactants cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB) by reducing Au 3+ ions with tryptophan. Interestingly, triangular shaped particles were seen to form in presence of CTAB, while spherical nanoparticles resulted with CTAC. The highlight of this result is the white light emission from the Au triangles obtained when CTAB is used. These results are supported by lifetime measurements and fluorescence.

Biogenic synthesis of Au and Ag nanoparticles by Indian propolis and its constituents

In an attempt to find natural, environmentally benign, green-chemical agents for the synthesis of metal nanoparticles, we have demonstrated for the first time the excellent efficiency of ethanol and water extracts of a natural, non-toxic material, Indian propolis and two of its chemical constituents, pinocembrin and galangin in the rapid synthesis of stable Ag and Au nanoparticles having wide spectrum of fascinating morphologies. Both of these two extracts were found to be extremely efficient in the synthesis of Ag and Au nanoparticles under alkaline condition. For a given metal ion precursor, the kinetics of particle synthesis were remarkably similar in all the cases, as it is evident from the absorption spectra monitored over time. Moreover they exhibited similar redox behavior under alkaline condition (pH ∼ 10.62). The efficiency of the ethanol and water extracts of Indian propolis towards Ag and Au nanoparticles synthesis was compared with that of naturally occurring hydroxyflavonoids, pinocembrin and galangin isolated from Indian propolis; which are equally efficient in the rapid synthesis of Ag and Au nanoparticles and stabilization of the resultant particles.

Determination of the Stability Constant of the Intermediate Complex during the Synthesis of Au Nanoparticles Using Aurous Halide

Little is known about the chemical equilibrium formed between the micellar complex of oleylamine and aurous halide during the synthesis of Au nanoparticles employing an Au(I) precursor. In this paper, we determine for the first time the stability constant of the intermediate oleylamine/Au complex during the first stages of the reaction that produces Au nanoparticles using an amine compound as a reducing agent. We found that the intermediate complex has two stability constants that were dependent on the concentration of AuCl. These results were supported by Fourier transform infrared and mass spectroscopy analysis, which indicated that an unstable secondary amine was produced during the oxidation of oleylamine and reduction of Au(I). Our findings demonstrate that the reduction of Au(I) species promotes substeps of structural changes in the oleylamine molecule. We anticipate our assays to be a starting point for a more comprehensive understanding of the synthesis of Au nanoparticles based on a templateless ...

Synthesis of Monodisperse Quasi-Spherical Gold Nanoparticles in Water via Silver(I)-Assisted Citrate Reduction

We demonstrate a simple and reproducible way to produce quasi-spherical Au nanoparticles (NPs) with a fairly narrow size distribution in water by rapidly adding a mixture solution of HAuCl(4), sodium citrate, and a trace amount of silver nitrate into boiling water. The sizes of quasi-spherical Au NPs obtained increases from 12 +/- 1 nm to 18 +/- 3, 25 +/- 3, and 36 +/- 3 nm with decrease of the citrate concentration in a fairly linear way. The present protocol can efficiently minimize the effect of citrate to buffer the pH of the reaction media and thus change the type and reactive activity of auric ions and significantly speed up the nucleation and growth rate of Au NPs. The presence of Ag(+) ions can not only suppress the secondary nucleation but also reshape the polycrystalline Au NPs into a quasi-spherical shape. In the case of synthesis of Au NPs of sizes ranging from 10 to 36 nm, our approach efficiently makes up the shortages of the classical Turkevich method with respect to the reproducibility and uniformity of the NP size and shape.