Size-controlled Gold Nanoparticles Research Articles

Rate redox-controlled green photosynthesis of gold nanoparticles using H3 + x PMo12 − x V x O40

Stabilized and size-controlled gold nanoparticles were synthesized using molybdophosphoric acid (H3[PMo12O40], HPMo) and its vanadium-substituted mixed addenda (H3 + x [PMo12 − x V x O40], (x = 0–3); and HPMoVx) under UV irradiation by a simple green method. In the process, HPMo and HPMoV x play the role of photocatalyst, reducing agent and efficient stabilizer. Control of gold nanoparticles size was achieved by variation of initial gold ions concentration and molar ratio of HPMo to gold ions. The synthesis rate of Au nanoparticles was found to be parallel to an increasing x value in the order of: HPMoV3 > HPMoV2 > HPMoV > HPMo, which leads to smaller and more uniform particles. Also, by substitution of vanadium instead of molybdenum in the HPMo formula, the morphology of nanoparticles was gradually changed from spherical-shaped nanoparticles in the presence of HPMo to nanorods in the case of HPMoV3.

Facile synthesis of biocompatible gold nanoparticles with organosilicone-coated surface properties

In this study, a simple method for one-step synthesis of gold nanoparticles has been developed using an organosilicone surfactant, Silwet L-77, as both a reducing and capping agent. Synthesis of gold nanoparticles using this method is rapid and can be conducted conveniently at ambient temperature. Further refinement of the method, through the addition of sodium hydroxide and/or silver nitrate, allowed fine control over the size of spherical nanoparticles produced. Coated on the surface with organosilicone, the as-prepared gold nanoparticles were biocompatible and stable over the pH range from 5 to 12, and have been proven effective at transportation into MC3T3 osteoblast cells. The proposed method is simple, fast, and can produce size-controlled gold nanoparticles with unique surface properties for biomedical applications.

Nonionic Brij Surfactant-Mediated Synthesis of Raspberry-Like Gold Nanoparticles with High Surface Area

We report a rapid, simple, single-step, and high-yielding solution-phase synthesis of raspberry-like gold nanoparticles (Au RLNPs) with rich edges and high surface areas. Au RLNPs were synthesized through the reduction of HAuCl4 simply mediated by nonionic Brij surfactant in basic conditions without any other reducing agents or organic molecules. The synthesized nanoparticles possessed high surface areas and were stable in basic or neutral conditions, which are potentially useful structural factors for the applications. The unique, highly red-shifted surface plasmon resonances (SPRs) of Au RLNPS originate from their rough, raspberry-like surfaces. The sizes of Au RLNPs were controllable by varying the amounts of NaOH and HAuCl4. However, there are very few reported facile syntheses of size-controlled multi-branched gold nanoparticles simply mediated by surfactant without any other reducing agents or organic molecules.

Size Control of Gold Nanoparticles Synthesized by Laser Ablation in Liquid Media

We investigate the influence of salt, acidic, and basic solutions (citrate, NaOH, and HCl) on the size of gold nanoparticles (AuNPs) synthesized by laser ablation in aqueous media. We found that NP size increases from 3 nm to 13 nm when Zeta potential varies from −100 mV to −10 mV whatever the concentration and the nature of chemical solution are namely, citrate, NaOH, and HCl. These results demonstrated that the final size of gold NPs produced by laser ablation in liquid media is mainly governed by the charge-dependent growth mechanism.

Synthesis of nano-bio conjugates for drug delivery systems using gas-liquid interfacial discharge plasmas

Size-controlled gold nanoparticles (AuNPs) covered with DNA are synthesized by using a pulsedriven gas-liquid interfacial discharge plasma (GLIDP) to reduce an aqueous solution of chloroauric acid trihydrate with DNA. The size and the assembly of the AuNPs are found to be easily controlled by changing the DNA concentration in the aqueous solution. The synthesized AuNP-DNA conjugates are forced to be encapsulated into double-walled carbon nanotubes (DWNTs) by superimposing a positive DC voltage on the pulse voltage. The AuNP-DNA-conjugate encapsulated DWNTs can be utilized in drug delivery systems when DNA is used as a drug molecule.

Size-controllable synthesis of catalyst of gold nanoparticles with capping agents of natural chitosan

In this study, size-controllable gold nanoparticles (NPs) are synthesized by using sonoelectrochemical methods in the presence of natural chitosan (Ch). First, positively charged Au-containing complexes were prepared in 0.1N NaCl by using oxidation–reduction cycle (ORC) treatment to Au substrate. Then size-controllable Au NPs, ranging from 10 to 80nm in diameter, were synthesized by varying the addition quantities of Ch from 1 to 2g/L, respectively, in solutions under using sonoelectrochemical reduction. Experimental results indicate that the optimal molar ratio of used Ch to synthesized Au NPs is ca. 3 for obtaining the smallest Au NPs. Moreover, the catalytic activity of the size-controllable Au NPs on the decomposition of acetaldehyde in solution was examined. Au NPs with 10nm in diameter demonstrate significantly catalytic activity. However, bigger Au NPs with 80nm in diameter are almost inert for the decomposition of acetaldehyde.

In Situ Formation and Size Control of Gold Nanoparticles into Chitosan for Nanocomposite Surfaces with Tailored Wettability

The in situ formation of gold nanoparticles into the natural polymer chitosan is described upon pulsed laser irradiation. In particular, hydrogel-type films of chitosan get loaded with the gold precursor, chloroauric acid salt (HAuCl(4)), by immersion in its aqueous solution. After the irradiation of this system with increasing number of ultraviolet laser pulses, we observe the formation of gold nanoparticles with increasing density and decreasing size. Analytical studies using absorption measurements, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy of the nanocomposite samples throughout the irradiation procedure reveal that under the specific irradiation conditions there are two competing mechanisms responsible for the nanoparticles production: the photoreduction of the precursor responsible for the rising growth of gold particles with increasing size and the subsequent photofragmentation of these particles into smaller ones. The described method allows the localized formation of gold nanoparticles into specific areas of the polymeric films, expanding its potential applications due to its patterning capability. The size and density control of the gold nanoparticles, obtained by the accurate increase of the laser irradiation time, is accompanied by the simultaneously controlled increase of the wettability of the obtained gold nanocomposite surfaces. The capability of tailoring the hydrophilicity of nanocomposite materials based on natural polymer and biocompatible gold nanoparticles provides new potentialities in microfluidics or lab on chip devices for blood analysis or drugs transport, as well as in scaffold development for preferential cells growth.

Size control of gold nanoparticles by intense X-ray irradiation: the relevant parameters and imaging applications

We report the analysis of a reducing-agent-free synthetic method based on intense X-ray irradiation in the presence of 11-mercaptoundecanoic acid (MUA) and their application in biomedical imaging. The method is very effective in controlling the size and size distribution of Au nanoparticles in colloidal solutions: gold nanoparticles (AuNPs) as small as ∼1.2 ± 0.25 nm are synthesized in a one-pot irradiation procedure without reducing agents. We found two coexisting properties of these small AuNPs: a strong visible fluorescence and very high accumulation in cells, which enabled a new type of multimodality imaging using X-ray and visible light microscopies. These properties come as a direct consequence of the precise size control; specifically, they exist only when the particle size is smaller than ∼1.4 nm. We found that this process critically depends on several parameters including the solution pH, the solution temperature and the irradiation time. Most important is the fact that the increase of the irradiation time is not necessarily beneficial, since an optimum value exists to obtain small particles with a narrow size distribution. The 1.4 nm AuNPs are not toxic and significantly accumulate in tumor tissues in animal tests, as confirmed by X-ray imaging and fluorescence microscopy. This biodistribution could open the way for the use of these nanoparticles in X-ray imaging.

Direct growth of size-controlled gold nanoparticles on reduced graphene oxide film from bulk gold by tuning electric field: effective methodology and substrate for surface enhanced Raman scattering study

Electric field dependent size-controlled gold nanoparticles (NPs), with a mean size ranging from 8 nm to more than 60 nm, are directly grown from bulk gold onto reduced graphene oxide (rGO) film in 0.2 M HCl aqueous solutions by electrochemical method. The Au NPs' distribution, from gradient with small area uniformity to the large area homogeneous all over the rGO film, is fully dependent on the electric field distribution between two electrodes. The particle size could be controlled by both the applied voltage and reaction time. By employing a uniform electric field, a high density Au NPs–graphene hybrid film with the particle size of tens of nanometres could be obtained for a surface enhanced Raman scattering (SERS) active substrate showing a high sensitivity of detecting rhodamine B molecules with the concentration as low as nM level, which may offer an effective way for size and distribution controlled fabrication of graphene based noble metal nanocomposites for potential utilization in detection and catalysis.

Electroless Growth of Size-Controlled Gold Nanoparticles Using Hydroquinone

Preparation of size-controlled gold nanoparticles is required for their use in applications. Electroless growth of gold nanoparticles using Au seeds with mean diameter of 12.5 nm and hydroquinone was performed and the growth process was analyzed. The pH dependencies of the redox potentials of hydroquinone and Au(III) ionic species were evaluated to investigate the growth mechanism of the nanoparticles in detail. Furthermore, the deposition behavior of Au in the growth solution was clarified by measuring the deposition weight of Au and the mixed potential during the growth of Au nanoparticles. Size control of Au nanoparticles was achieved by changing the concentration of Au seeds in the Au growth solution, allowing Au nanoparticles with a mean diameter of 38.7-63.5 nm to be successfully obtained.

Synthesis and stability evaluation of size-controlled gold nanoparticles via nonionic fluorosurfactant-assisted hydrogen peroxide reduction

We report an aqueous synthesis of gold nanoparticles (AuNPs) by chemical reduction of HAuCl4 with hydrogen peroxide (H2O2) in the presence of nonionic fluorosurfactant (FSN). Here, FSN acts as a co-reducing and stabilizing agent. The diameters of the FSN-stabilized spherical AuNPs were 18 ± 3.8, 23 ± 2.5, 29 ± 3.4, 36 ± 4.0 nm by varying the H2O2–gold molar ratio. The formation mechanism of the FSN-stabilized AuNPs was proposed by UV-visible spectroscopy, powder X-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) images, Fourier transform infrared (FT-IR) spectroscopy, and electronic spinning resonance (ESR) measurements. High temperature decomposition of H2O2 can generate hydroxyl radicals (˙OH), which can rapidly oxidize R–CH2CH2–OH in FSN molecules to R–CH2CH˙–OH radicals. The rapid formation of Au(0) is ascribed to the reduction of Au(III) by R–CH2CH˙–OH radicals. The Au(0) aggregation on the gold crystal nucleus is restrained due to the steric hindrance effect of FSN ligands, leading to the formation of small AuNPs. More interestingly, the FSN-stabilized AuNPs show excellent colloidal stability in the presence of high salt concentrations and over a wide range of pH values (2–11) without particle aggregation at room temperature for at least one month.

A facile and one-step colorimetric determination of hydrazine during formation of size-controlled amidosulfonic acid capped gold nanoparticles

A facile and one-step colorimetric detection of hydrazine has been developed for the first time during the formation of size-controlled amidosulfonic acid capped gold nanoparticles (AA-AuNPs). Hydrazine served not only as a target analyte but also a reductant to react with chloroauric acid (HAuCl4). In order to obtain size-controlled gold nanoparticles (AuNPs), the amidosulfonic acid (AA) was used as a stabilizer. In the presence of AA, different aggregation states of AuNPs, which exhibited distinct color changes, were obtained by varying the concentration of hydrazine. Furthermore, the changes of color resulted in different ultraviolet visible (UV-Vis) absorptions, which realized quantitative analysis of hydrazine. The detection results indicated that the proposed method exhibited good performance for hydrazine determination with a wide linear range from 1.0 × 10−7 to 2.53 × 10−4 M (r = 0.9915) and a low detection limit of 8.53 × 10−8 M. The proposed method was successfully used in detecting hydrazine in various real water samples with high selectivity, sensitivity and reliability. Even outdoors, the proposed method could also be applied in real time to determine whether the hydrazine concentration was permitted or not in water samples via the visible color change.

Size-Controlled Gold Nanoparticles Synthesized in Solution Plasma

Size-controlled gold nanoparticles (NPs) have been synthesized using an electrical discharge in a liquid environment, termed solution plasma processing (SPP). The gold NPs exhibit sizes from 1 to 2 to 10 nm when the solution pH was adjusted in the range from 12 to 3, respectively. The chemical environment surrounding the gold NPs depends on the preparation conditions and determines the electrostatic interaction among the nanoparticles, which alters their final size. Information obtained from XPS analysis, ToF-SIMS mass spectra, and UV–vis absorption spectroscopy were consistent and demonstrate that the gold NPs are partially oxidized on the surface, when synthesized in a pH 12 solution, and remain surrounded by gold chloride compounds when synthesized in a pH 3 solution. Plasma diagnostics shows that a high electron density contributes to generating a larger number of hydrogen radicals, which represent the main component in the reduction process of the gold ion into the neutral form.

Room temperature O2 plasma treatment of SiO2 supported Au catalysts for selective hydrogenation of acetylene in the presence of large excess of ethylene

Supported gold nanoparticles have been proven to be active in the hydrogenation of the acetylene. In this work, we applied gold nanoparticles supported on silica for the selective hydrogenation of acetylene in excess ethylene that was close to current industrial practices. Amine group surface-functionalized silica was used to absorb the gold precursor AuCl4-, and small size-controlled gold nanoparticles are formed after chemical reduction. For the first time, O2 plasma was employed to remove the APTES grafted on the surface of silica for preparing the highly dispersed gold nanoparticles (∼3nm). The results of IR, TGA, XRD, and TEM showed that O2 plasma working under mild conditions (room temperature and low pressure) can efficiently remove the organic compounds without causing the aggregation of the gold nanoparticles. The plasma-treated catalyst Au/SiO2 gave excellent low-temperature selective catalytic activity in the hydrogenation of acetylene. The effects of the reduction temperatures on the catalytic performances of the Au/SiO2 were investigated. The enhanced performance of gold nanoparticles supported on silica as pretreated by O2 plasma was ascribed to two effects: (1) the small size of the gold nanoparticles supported on silica, (2) the nearly neutral charge on the Au nanoparticle, which is favorable to the activation of hydrogen.

Gold aggregates on silica templates and decorated silica arrays for SERS applications

In this work, we report the fabrication and characterization of size controllable gold nanoparticles (NPs) aggregates for their application in surface enhanced Raman scattering (SERS). Aggregates were prepared using two methodologies: (i) by using silica particles arrays as a template to agglomerate gold NPs between the inter-particle interstices, and (ii) by functionalizing silica particles to be used as support to graft gold nanoparticles and thus to form decorated silica particle arrays. These substrates were used in the detection of Rhodamine 6G producing an enhancement factor (EF) from 104 to 106 that is associated to the increment of hot spot (HS) sites, and the fact that plasmon resonance from aggregates and absorption wavelength of test molecules are closely in resonance with excitation wavelength. The EF was also reduced when the plasmon resonance was red-shifted as a result of the increment of aggregate size. In spite of this, the EF is high enough to make these SERS substrates excellent candidates for sensing applications.

Controlled synthesis of gold nanoparticles by fluorescent light irradiation

A novel photochemical synthesis of size-controlled gold nanoparticles wasreliably accomplished via both a direct reduction and a seeded-growth methodat room temperature under the irradiation of fluorescent light. These methodsutilized the intensity of fluorescent light that closely resembles daily sunlight (∼100 mW cm − 2). This effectively allowed for the formation of gold nanoparticles with tunable sizes simplyby controlling the concentration of trisodium citrate and gold chloride. The broad bandfluorescent light was found to be an efficient source for inducing the formation of goldnanoparticles at ambient conditions. The size distribution and absorption property of theresulting nanoparticles were thoroughly characterized by scanning/transmission electronmicroscopy, dynamic light scattering, UV–visible spectroscopy and powder x-raydiffraction. This photochemical synthesis demonstrates, for the first time, the reliablepreparation of gold nanoparticles at room temperature upon irradiation with fluorescentlight.

Studies on the Effect of the Capping Materials on the Spherical Gold Nanoparticles Catalytic Activity

Size-controlled gold nanoparticles (AuNPs) were prepared in the presence of different capping materials (sodium citrate, cetyltrimethylammonium bromide (CTAB), and chitosan). The results obtained suggest that the AuNPs were synthesized with different particle size, which is controlled by changing the molar ratio between sodium citrate, (CTAB), and chitosan to Au (III). The catalytic activities of the AuNPs with different capping materials were studied for 4-nitrophenol reduction by NaBH4 as a model reaction. AuNPs with different capping materials is comparable from the value of the apparent rate constant of 4-nitrophenol reduction (0.6 × 10–3, 1.9 × 10–3, and 2.4 × 10–3 s–1) for sodium citrate, CTAB and chitosan. From the results, it is concluded that, AuNPs catalyzed the electron transfer process between and nitro compounds with all the capping materials used AuNPs capped by chitosan were more active for the reduction than the other two.

Facile preparation of size-controlled gold nanoparticles using versatile and end-functionalized thioether polymer ligands

At present, thiol ligands are generally used whenever the classical Brust-Schiffrin two-phase method is employed to prepare metal nanoparticles. In general, the previous research was mainly focused on utilizing small molecular thiol compounds or thiol polymers as the stabilizers in organic phase to obtain small sized and uniform gold nanoparticles (Au NPs). Such preparations are usually associated with the problems of ligand exchange on the nanoparticle's surface due to strong Au-thiol interaction. Herein, we report an approach to produce fairly uniform Au NPs with diameters about 2-6 nm using thioether end-functional polymer ligands (DDT-PVAc and PTMP-PVAc) as the capping agents. These nanoparticles are thoroughly characterized using DLS, TEM, UV-Vis spectroscopy and other complementary techniques. The results indicate that multidentate thioether polymeric ligands (PTMP-PVAc) lead to formation of smaller but special 'multimer' morphology in organic phase; whereas fairly uniform nanoparticles are produced using monodentate thioether functionalized ligands (DDT-PVAc). Further modification of such polymer ligands to introduce the hydrophilic functionalities realizes the phase transfer of Au NPs from organic to aqueous media.

Polyphenol-grafted collagen fiber as reductant and stabilizer for one-step synthesis of size-controlled gold nanoparticles and their catalytic application to 4-nitrophenol reduction

A facile method for one-step synthesis of size-controlled gold nanoparticles (AuNPs) supported on collagen fiber (CF) at room temperature was proposed. Epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface to serve as reducing/stabilizing agent, so that the AuNPs were generated on CF surface without introduction of extra chemical reagents or physical treatments. The prepared AuNPs were fully characterized, and the results showed that the dispersed AuNPs were successfully produced and the mean particle size of AuNPs could be effectively controlled in range of 18 to 5 nm simply by varying the grafting degree of EGCG on CF surface. These stabilized AuNPs were found to be active heterogeneous catalysts for the reduction of 4-nitrophenol to 4-aminophenol in aqueous phase. The catalytic behaviors of AuNPs depended on the particle size and the grafting degree of EGCG. A distinct advantage of these catalysts is that they can be easily recovered and reused at least twenty times, because of the high stability of the AuNPs supported by EGCG-grafted CF.

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.