Colloidal Au Nanoparticles Research Articles

Seeded Growth of Large-Area Arrays of Substrate Supported Au Nanoparticles Using Citrate and Hydrogen Peroxide.

While seeded growth of quasi-spherical colloidal Au nanoparticles (NPs) has been extensively explored in the literature, the growth of surface supported arrays of such particles has received less attention. The latter scenario offers some significant challenges, including the attainment of sufficient particle-substrate adhesion, growth-selectivity, and uniform mass-transport. To this end, a reaction system consisting of HAuCl4, citrate, and H2O2 is here investigated for the growth of supported arrays of 10 nm Au seeds, derived via block copolymer (BCP) lithography. The effects of the reagent concentrations on the properties of the resultant NPs are evaluated. It is found that inclusion of citrate in the growth medium causes substantial particle desorption from Si surfaces. However, the presence of citrate also yields NPs with more uniformly circular top-view cross sections (“quasi-circular”), motivating the exploration of particle immobilization methods. We demonstrate that atomic layer deposition (ALD) of a single cycle of HfO2 (∼1 Å), after the seed particle formation, promotes adhesion sufficiently to enable the use of citrate without the added oxide noticeably affecting the shape of the resultant NPs. The presented ALD-based approach differs from the conventional sequence of depositing the adhesion layer prior to the seed particle formation and may have advantages in various processing schemes, such as when surface grafting of brush layers is required in the BCP lithography process. A proof-of-concept is provided for the growth of large-area arrays of supported “quasi-circular” Au NPs, in a rapid one-step process at room temperature.

Gold Nanoparticle-Enhanced and Roll-to-Roll Nanoimprinted LSPR Platform for Detecting Interleukin-10.

Localized surface plasmon resonance (LSPR) is a powerful platform for detecting biomolecules including proteins, nucleotides, and vesicles. Here, we report a colloidal gold (Au) nanoparticle-based assay that enhances the LSPR signal of nanoimprinted Au strips. The binding of the colloidal Au nanoparticle on the Au strip causes a red-shift of the LSPR extinction peak, enabling the detection of interleukin-10 (IL-10) cytokine. For LSPR sensor fabrication, we employed a roll-to-roll nanoimprinting process to create nanograting structures on polyethylene terephthalate (PET) film. By the angled deposition of Au on the PET film, we demonstrated a double-bent Au structure with a strong LSPR extinction peak at ~760 nm. Using the Au LSPR sensor, we developed an enzyme-linked immunosorbent assay (ELISA) protocol by forming a sandwich structure of IL-10 capture antibody/IL-10/IL-10 detection antibody. To enhance the LSPR signal, we introduced colloidal Au nanocube (AuNC) to be cross-linked with IL-10 detection antibody for immunogold assay. Using IL-10 as a model protein, we successfully achieved nanomolar sensitivity. We confirmed that the shift of the extinction peak was improved by 450% due to plasmon coupling between AuNC and Au strip. We expect that the AuNC-assisted LSPR sensor platform can be utilized as a diagnostic tool by providing convenient and fast detection of the LSPR signal.

XPS study of interactions between linear carbon chains and colloidal Au nanoparticles

The X-ray photoelectron spectra (XPS) of Au colloidal nanoparticles (Au NPs) and Au–NPs/linear carbon chain (LCC) structures (Au@LCC) prepared by nanosecond pulsed laser ablation in liquid water were measured. The Au 4f XPS peaks of Au NPs coincided with those of metallic gold to confirm that a metallic state was retained in colloidal Au nanoparticles. On the other hand, the Au 4f XPS spectra of Au@LCC showed a low-energy broadening due to the formation of Au–C bonds between Au NPs and LCC.

Surface-enhanced Raman spectroscopy (SERS) investigations of saliva for oral cancer diagnosis.

Saliva could be an optimal sample for non-invasive cancer detection, as it contains plenty of proteins and metabolites which can reflect the health status of an individual. Moreover, pairing it with high-sensitivity, label-free detection techniques could prove successful for early cancer diagnosis. In this study, we explore the enhancement of salivary characteristic Raman bands by using label-free, ultrasensitive surface-enhanced Raman scattering (SERS) based on gold nanoparticles. SERS maps were acquired from dry samples of saliva supernatant mixed with Au colloidal nanoparticles, which was then pipetted on clean glass slides. The SERS spectra presented a high variability of signal intensities and frequency shifts. However, several reproducible SERS spectra showing well-resolved bands were obtained at certain locations on the maps, where Au nanoparticles clustered together during the air-drying. The healthy and oral cancer saliva could be differentiated using principal components analysis based on several SERS bands assigned mainly to amino acids and proteins. Moreover, thiocyanate Raman modes were detected in saliva samples of both smoking and non-smoking volunteers and cancer patients. The analysis indicated that the cancer group displayed an overall higher level of the 2126cm-1 band area assigned to C-N stretching vibrations of thiocyanate.

Dendrimer‐Based Gold Nanostructures for SERS Detection of Pesticides in Water

Dendrimers are polymers with well‐defined architectures and tunable chemistry, which make them useful in a number of applications. Herein, the chemistry of poly(amido)amine (PAMAM) dendrimers with different functional groups was explored to produce a variety of plasmonic systems based on Au colloidal nanoparticles. The resulting systems present long‐term colloidal stability and were investigated as sensitive platforms for surface‐enhanced Raman scattering (SERS). The application of these SERS platforms for the detection of water trace pollutants, was explored through the analysis of selected pesticides. Noteworthy, dendrimer coated Au nanoparticles with tunable properties such as size, shape and surface chemistry, were obtained by varying the dendrimer chemical properties. The surface chemistry of PAMAM capped Au colloids was explored in order to produce target selective SERS substrates for pesticide detection, that allowed to reach detection limits down to 10 nm.

Ultrastable Au nanoparticles on titania through an encapsulation strategy under oxidative atmosphere

Supported gold catalysts play a crucial role in the chemical industry; however, their poor on-stream stability because of the sintering of the gold nanoparticles restricts their practical application. The strong metal-support interaction (SMSI), an important concept in heterogeneous catalysis, may be applied to construct the structure of catalysts and, hence, improve their reactivity and stability. Here we report an ultrastable Au nanocatalyst after calcination at 800 °C, in which Au nanoparticles are encapsulated by a permeable TiOx thin layer induced by melamine under oxidative atmosphere. Owning to the formed TiOx overlayer, the resulting Au catalyst is resistant to sintering and exhibits excellent activity and stability for catalytic CO oxidation. Furthermore, this special strategy can be extended to colloidal Au nanoparticles supported on TiO2 and commercial gold catalyst denoted as RR2Ti, providing a universal way to engineer and develop highly stable supported Au catalysts with tunable activity.

Synthesis of Colloidal Au Nanoparticles through Ultrasonic Spray Pyrolysis and Their Use in the Preparation of Polyacrylate-AuNPs' Composites.

Colloidal gold nanoparticles (AuNPs) were prepared from two different liquid precursors (gold (III) acetate and gold (III) chloride), using the Ultrasonic Spray Pyrolysis (USP) process. The STEM characterisation showed that the AuNPs from gold chloride are spherical, with average diameters of 57.2 and 69.4 nm, while the AuNPs from gold acetate are ellipsoidal, with average diameters of 84.2 and 134.3 nm, according to Dynamic Light Scattering (DLS) measurements. UV/VIS spectroscopy revealed the maximum absorbance band of AuNPs between 532 and 560 nm, which indicates a stable state. Colloidal AuNPs were used as starting material and were mixed together with acrylic acid (AA) and acrylamide (Am) for the free radical polymerization of polyacrylate-AuNPs’ composites, with the purpose of using them for temporary cavity fillings in the dental industry. SEM characterisation of polyacrylate-AuNPs’ composites revealed a uniform distribution of AuNPs through the polymer matrix, revealing that the AuNPs remained stable during the polymerization process. The density measurements revealed that colloidal AuNPs increase the densities of the prepared polyacrylate-AuNPs’ composites; the densities were increased up to 40% in comparison with the densities of the control samples. A compressive test showed that polyacrylate-AuNPs’ composites exhibited lower compressive strength compared to the control samples, while their toughness increased. At 50% compression deformation some of the samples fracture, suggesting that incorporation of colloidal AuNPs do not improve their compressive strength, but increase their toughness significantly. This increased toughness is the measured property which makes prepared polyacrylate-AuNPs potentially useful in dentistry.

Preformed Au colloidal nanoparticles immobilised on NiO as highly efficient heterogeneous catalysts for reduction of 4-nitrophenol to 4-aminophenol

A facile approach to synthesise highly active and stable Au/NiO catalysts for the hydrogenation of nitro-aromatics is reported. Preformed gold nanoparticles have been immobilized onto NiO using a colloidal method. In this article, the reduction of 4-nitrophenol with NaBH4 has been used as a model reaction to investigate the catalytic activity of synthesised Au/NiO catalysts. In addition, we report a systematic study of the reduction kinetics, and the influence of specific reaction parameters such as (i) temperature, (ii) stirring rate, (iii) sodium borohydride concentration and (iv) substrate/metal molar ratio. The reaction has been performed at a substrate/metal molar ratio of 7.4, a ratio significantly higher than previously reported. Reusability of the catalyst has been examined, with little to no decrease in activity observed over 5 catalytic cycles. Systematic variation of Au loading reveals the successful synthesis of low cost and efficient Au/NiO catalysts at very low Au content and using high substrate/metal molar ratios.

Gold-Coated Superparamagnetic Iron Oxide Nanoparticles Attenuate Collagen-Induced Arthritis after Magnetic Targeting.

The aim of the study was to evaluate if gold-coated superparamagnetic iron oxide nanoparticles (AuSPION)magnetic-targeted to the arthritic articulation of collagen induced arthritis (CIA) rats are able to ameliorate rheumatoid arthritis without producing significant biological adverse effects in comparison to colloidal Au nanoparticles (AuC) and metotrexate (MTX). Male Wistar rats were divided into control; arthritic; AuSPION (150μgkg-1); AuC (150μgkg-1) and MTX (2.5μgkg-1). Treatments were administered thrice every other day by the intraperitoneal route 15min after all groups had a neodymium magnet coupled to the right ankle joint (kept for 1h). Paw edema and body weight were measured weekly. Joint sections were evaluated by Haematoxylin & Eosin and immunohistochemistry (TNF-α, IL-1β). Biomarkers of oxidative stress were used to evaluate toxicity. Among the evaluated treatments, AuSPION led to significant clinical improvements (decreased edema and infiltration by leukocytes as well as less positively immunostained cells for both TNF-α and IL-1β in synovium) accompanied by a lack of toxicity as indicated by redox state and genotoxicity assays. Our results clearly indicate that the magnetic targeting of AuSPION suppresses joint edema and inflammation, cytokine expression as well as the redox imbalance, thereby contributing to an amelioration of arthritis severity in CIA rats. The results demonstrate for the first time the potentiality of AuSPION administration under a magnetic field as an attractive alternative for future treatments of rheumatic diseases.

Well-Controlled Generation Process of Bimetallic Ag//Au Colloidal Nanoparticles by Non-Thermal Plasma DC Glow Discharge

In this paper, an inexpensive, simple and well-accurate process of the generation of bimetallic silver Ag//gold Au core//shell is colloidal metal nanoparticles (MNPs). This is achieved via an atmospheric pressure non-thermal plasma glow discharge between two electrodes. One of these electrodes is a capillary tube placing over solution about (1 cm) that acts as the cathode, while the other electrode is a metal disk immersed in the solution and acts as an anode. Glow discharge process carried out at room temperature using a home-made cell with (6 KV) applied voltage and direct current (DC) about (1.8 mA) for different discharge periods. A wide range of bimetallic Ag//Au colloidal MNPs was rapidly synthesized as a result of non-thermal plasma formation between a capillary tube and the surface of AgNO3 solution for (5 min) and a mixture of AgNPs-HAuCl4 solution for (5, 10 and 15 min). Field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction were used to investigate the structural properties of the bimetallic Ag//Au colloidal MNPs. While optical properties were investigated using a UV-Vis spectrophotometer. Results show that the discharge time plays a crucial role in modifying the bimetallic nanoparticles properties such as grain size, surface area, and optical stability. Moreover, TEM and FE-SEM confirm the formation of Ag//Au core//shell structure with uniform sizes and shapes.

Synthesized and Characterizing of (Au@Pt) Ultra Fine Nanoparticles Prepared by Pulsed Laser Ablation in Liquids

Gold(Au), Platium (Pt) and Gold –Coated Platinum (Au@Pt) ultra Fine(UF) nanoparticles (NPs) were preperd by Pulsed Laser Ablation in Liquids method with (Q-switched, 1064 doubled frequency-Nd: YAG). The laser ablation of Au ,Pt metal plates and (Au@Pt) has been performed by immersing these metal plates in two different liquid deionised water (DIW) and ethanol alcohol . (PLAL) process preformed with 100 pulse energy of 700 mJ and liquid depth is 2cm. The nanoparticles of the gold element were coated with platinum(Au@Pt) in two steps. The nanotubes of the gold element were first examined and the platinum metal was then immersed in the liquid from the first step. The formation efficiency of PLAL process was quantified in terms of the absorption spectrum peaks. The absorption spectra ( Pt) in DIW shows a sharp and single peak around 234nm, and (Au@Pt) shows a sharp and single peak for Au at 516nm and for Pt 221nm. The TEM images show that the nanoparticles are rather spherical in shape. While the average size for all the samples was in rang from(2-5)nm. There was an increase in size when using ethanol alcohol. Changing the way of the fluid environment is a simple and flexible way to control the size and strength of Au and Pt and (Au@Pt) colloidal nanoparticles.

Facile Film-Nanoctahedron Assembly Route to Plasmonic Metamaterial Absorbers at Visible Frequencies.

Plasmonic metamaterial absorbers (MAs) with broadband and near-perfect absorption properties in the visible region were successfully fabricated via a facile film-colloidal nanoparticle (NP) assembly method. In this approach, colloidal octahedral Au NPs were employed as the surface meta-atoms of MAs, whereas nanoscale-thick SiO2 and Al films were used as the dielectric spacer and reflector, respectively. It is worth noting that the Au nanoctahedra were randomly assembled onto the Al-SiO2 films, and no effort was made to precisely control their spatial arrangements. The optical characterization showed that the as-prepared MAs exhibited broadband high absorption (average absorptivity above 85%) within the whole visible spectrum for a broad range of incident angles (0°-60°). In particular, two polarization-independent near-perfect absorption peaks (absorptance above 99%) were recorded near 540 and 727 nm, respectively. Moreover, the absorption properties of the MAs can be effectively controlled and tailored by varying the geometry (the thickness of the dielectric spacer and the surface coverages of the Au nanoctahedra). Electromagnetic simulations further demonstrated that enhanced Mie resonances and strong plasmonic coupling effects were critical for the designed MAs. This work here may provide an efficient and alternative route for the design of scalable visible light absorbers for applications such as solar cells, photothermalvoltaics, and biochemical sensors.

Surface plasmon assisted laser ablation of stainless steel

Colloidal Au nanoparticles (NPs) were decorated on stainless steel for surface plasmon enhanced laser ablation. A comparative study of the laser ablation efficiency was carried out on stainless steel samples with and without the Au NPs decoration at a variable pulsed laser fluence and laser pulse number. Higher ablation efficiency was clearly demonstrated in the former as illustrated from the larger diameter, maximum depth and the cross-sectional area of the crater generated by the laser ablation under the same conditions. Additionally, both the maximum depth and efficiency enhancement were found to depend on the laser fluence and pulse number. The maximum enhanced ablation efficiency of 36% based on the cross-sectional area of the crater was obtained at 1 pulse number of laser fluence 1.53 J cm−2. The efficiency enhancement of laser ablation is attributed to the highly enhanced surface plasmon field at the interface between Au NPs and stainless steel.

Effect of electrophoresis time deposition of colloidal gold nanoparticles on inducing the crystallization of amorphous Si thin films

This work investigates the metal induced crystallization of hydrogenated amorphous Silicon (a-Si:H) thin films, processed by plasma enhanced chemical vapor deposition, using Au nanoparticles (AuNPs) as crystallizing mediator metal. Electrophoresis deposition (EPD) of colloidal AuNPs was used to coat the Si substrates before the a-Si:H processing. Then, the crystallization was conducted by isothermal annealing for temperatures above the eutectic (500 and 600 °C). Raman spectroscopy analysis showed that the crystalline volume fraction doubled as the EPD time increases. Scanning electronic microscopy and energy-dispersive X-ray microanalysis revealed that AuNPs induced crystallization at 600 °C was achieved through eutectic reaction with mixing layers. Structural characterizations showed that the low amounts of AuNPs exhibited a metal mediating effect more pronounced than that of continuous Au thin film deposited by dry physical methods. The enhancing effect of AuNPs was assigned to their size dependent high surface energy. Herein, we discuss as well, the effect of the EPD time on the development of Si crystallites on the basis of thermodynamic and kinetic considerations.

Colloidal synthesis of Au nanoparticles using polyelectrolytes with 1,3,4‐thiadiazole as reducing agents

ABSTRACTHeterocyclic compounds are well known for their biological activity and coordination properties. Some heterocyclic compounds have been employed in the stabilization against coalescence of metallic nanoparticles in colloidal solutions, for example, tetrazole, triazole, and pyrazole. The aim of this work is to design new polyelectrolytes with heterocyclic pendant groups useful as reducing agents of Au3+ and as stabilizing agents for the synthesis of colloidal Au nanoparticles. Thus, polyelectrolytes with thiosemicarbazone and 1,3,4‐thiadiazole pendant groups were used as reducing agents of Au3+ ions and stabilizing agents of Au nanoparticles. The voltammetry study of the polyelectrolytes showed that one with thiosemicarbazone pendant groups is the better reducing agent than polyelectrolytes with heterocyclic pendant groups. The polyelectrolytes can control the growth of the nanoparticles, obtaining structures with an average size of 9 nm. In this study, it was concluded that the nature of the heterocyclic group does not have an effect on the shape of nanoparticles and quasi‐spherical nanoparticles were obtained with all polyelectrolytes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47790.

Micropillar fabrication based on local electrophoretic deposition using a scanning ion conductance microscope with a theta nanopipette

We developed a novel local electrophoretic deposition technique using a scanning ion conductance microscope (SICM) with a double-barreled theta nanopipette. One channel of the nanopipette was used as a probe of the SICM function to control the pipette-substrate surface distance, and the other channel filled with Au colloidal solution was used for electrophoretic deposition. After positioning the pipette edge in the vicinity of the substrate using the SICM function, the colloidal Au nanoparticles were electrophoretically deposited on the substrate. The deposition was carried out in liquid environment, which realized reproducible fabrication by preventing the clogging of the pipette aperture from drying of the colloidal solution. By moving the pipette upward while maintaining the deposition, micropillars with submicrometer diameters were successfully fabricated. The mechanical properties of the fabricated pillar were evaluated using a commercial microcantilever by applying a loading force. The average Young’s modulus was calculated to be approximately 32 GPa.

Revealing the Role of Chain Length of Ligands on Gold Nanoparticles Surface in the Process for Catalysis Reduction of 4-Nitrophenol

The hindrance of ligands chain arising from colloidal nanoparticle (NPs) surface in the process for different kinds of colloidal Au NPs catalyzed reduction of 4-nitrophenol (4-NP) is presented. The hindrance around Au NPs is controlled by varying the length of chain ligands coated on Au NPs. As the length of the ligand chain shortens, the catalytic activity of colloidal Au NPs got significant promotion for the 4-NP reduction reaction. Till inorganic sulfide ion as surface ligand, the catalytic activity of Au@S2− NPs reached the top. Moreover, by grafting different organic chain ligands of quaternary ammonium salts into Au@S2− NPs to vary the length of ligands, we can realize the regulation of catalytic reaction rate during the procedure of the reduction of 4-NP. In particular, Au@S2− NPs also exhibited excellent catalytic cycle stability.

Hydrophobic Slippery Surface-Based Surface-Enhanced Raman Spectroscopy Platform for Ultrasensitive Detection in Food Safety Applications.

Collecting highly diluted target analytes into specific hot spot regions is vital for ultrasensitive surface-enhanced Raman spectroscopy (SERS) applications. In this work, a hydrophobic slippery platform was employedas a concentrator to construct colloidal SERS-active substrates regardless of the diffusion limits during droplet evaporation. Within only 140 s, sufficient absorption between the analytes and colloidal Au nanoparticles (Au NPs) was observed by fluorescence imaging. This effect resulted in excellent SERS sensitivity and stability. Compared with the common metal colloid-based SERS substrates, e.g.,drying on a silicon wafer or detection in colloidal solutions, this preconcentrated method showed lower detection limits and the lowest detectionconcentration of crystal violet molecule down to 10-12 M with a portable Raman spectrometer. Such high signal enhancement was mainly ascribed to the condensation effect of Au colloids/analytes on the hydrophobic slippery substrate, by which almost all probe molecules were guided into the "hot spot" regions of aggregated Au NPs. Using the SERS platform, various illegal additives in realistic food and health-care products, for example, malachite green (1 ppb) added in fish and morphine (0.1 ppm) added in a chafing dish, could be sensitively detected. Therefore, our protocol is a general SERS platform that may provide a simple, fast, and cost-effective approach for trace molecular sensing.

Extracting structural information of Au colloids at ultra-dilute concentrations: identification of growth during nanoparticle immobilization.

Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.

Size-controlled, high optical quality ZnO nanowires grown using colloidal Au nanoparticles and ultra-small cluster catalysts

Size-controlled ZnO nanowires were grown by eclipse pulsed laser deposition using Au colloids and ultra-small (sub 2 nm) Au101 and Au9 clusters as catalysts, tethered to c-plane sapphire substrates using aminopropyltrimethoxysilane (APTMS). A strong correlation was observed between ZnO nanowire tip diameter and Au catalyst size, with no apparent lower limit to the size of Au nanoparticles able to catalyze nanowire growth. All ZnO nanowires produced intense ultraviolet photoluminescence with almost no visible defect band emission that is commonly observed in ZnO-based materials, including nanowires. A correlation was also observed between the quality of the ultraviolet photoluminescence (in terms of decreasing exciton line widths and surface-related emission) and decreasing ZnO nanowire diameter, with the highest quality emission obtained using Au9 atomically precise cluster catalysts, used here as catalysts for ZnO growth for the first time.