Growth Of Gold Nanoparticles Research Articles

Kinetics and Mechanism of Metal Nanoparticle Growth via Optical Extinction Spectroscopy and Computational Modeling: The Curious Case of Colloidal Gold.

An overarching computational framework unifying several optical theories to describe the temporal evolution of gold nanoparticles (GNPs) during a seeded growth process is presented. To achieve this, we used the inexpensive and widely available optical extinction spectroscopy, to obtain quantitative kinetic data. In situ spectra collected over a wide set of experimental conditions were regressed using the physical model, calculating light extinction by ensembles of GNPs during the growth process. This model provides temporal information on the size, shape, and concentration of the particles and any electromagnetic interactions between them. Consequently, we were able to describe the mechanism of GNP growth and divide the process into distinct genesis periods. We provide explanations for several longstanding mysteries, for example, the phenomena responsible for the purple-greyish hue during the early stages of GNP growth, the complex interactions between nucleation, growth, and aggregation events, and a clear distinction between agglomeration and electromagnetic interactions. The presented theoretical formalism has been developed in a generic fashion so that it can readily be adapted to other nanoparticulate formation scenarios such as the genesis of various metal nanoparticles.

In Situ Liquid Cell TEM Studies on Etching and Growth Mechanisms of Gold Nanoparticles at a Solid–Liquid–Gas Interface

AbstractEtching and growth of gold nanoparticles at a solid–liquid–gas interface are investigated via in situ liquid cell transmission electron microscopy. For this purpose, the gold precursor tetrachloroauric acid is enclosed in the wells of a free‐standing, locally thinned silicon nitride film covered by few‐layer graphene. Etching of gold is attributed to hydroxide radicals generated by radiolysis and gaseous species which are located within a gas bubble. The etching mechanism comprises two distinct cases. In one case, the gas bubble is in direct contact with the gold particle, separated only by a thin liquid membrane. In the other case, the gold particle is thoroughly immersed in liquid in the vicinity of the particle. In the latter, etching molecules diffuse from the bubble through the liquid toward the surface of the nanoparticle and subsequently etch the gold platelet. During the particle etching process, concurrent nucleation and ripening of gold nanoparticles are observed. This growth is induced by local supersaturation of the solution with gold ions. Experimental results show that the growth process is limited by diffusion, even though the diffusivity of reactants is very low due to narrow‐channel effects compared against the diffusivity of solvated ions in bulk liquids.

Controlled In Situ Seed-Mediated Growth of Gold and Silver Nanoparticles on an Optical Fiber Platform for Plasmonic Sensing Applications

This study presents an in situ growth technique to develop highly sensitive plasmonic fiber optic sensors with an excellent control over the plasmonic properties of gold (AuNPs) and silver nanoparticles (AgNPs). Here, we exploit the dual functionality of the U-bent fiber optic sensor (FOS) probes, where the probe acts as, firstly, the substrate for nanoparticles’ growth and, secondly, an invaluable tool to monitor as well as control the gold and silver seed binding to the surface amine groups and subsequently their growth in real time by means of the evanescent wave absorbance (EWA) spectral response. Au and Ag seeds (< 5 nm) with a peak absorbance at 510 and 390 nm, respectively, were used. The NP growth kinetics from the probes for different seed densities with a peak EWA response of 0.05, 0.1, and 0.15 optical density (OD) were observed in the presence of the respective metal precursor, cetyltrimethylammonium bromide (CTAB), and ascorbic acid. In comparison with AuNP grown FOS, a significant anisotropic growth was observed for AgNP with a redshift and spectral width as high as 215 nm and 425 nm, respectively, for a peak EWA response of 2.0 OD. The localized surface plasmon resonance (LSPR) activity of the AuNPs and AgNP grown FOS probes was evaluated for seed density of 0.1 OD. These proof-of-the-concept studies show significantly high RI sensitivity and surface-enhanced Raman scattering (SERS) enhancement factor for AgNP probes at 15.8 ΔA/RIU (for 22 AgNPs/μm2) and 1.3 × 107, respectively, in comparison with 18.9 ΔA/RIU (for 1424 AuNPs/μm2) and 1.1 × 106, respectively, for AuNP FOS probes. In addition, these plasmonic probes were stable in organic solvent (hexane) but its stability was deteriorated in alkaline solution (1 M NaOH).

Time-Dependent Growth of Gold Nanoparticles: Experimental Correlation of van der Waals Contact between DNA and Amino Acids with Polar Uncharged Side Chains

Time-dependent investigation of growth reactions from 0.45 nM gold nanoparticle seeds in the presence of 9 mM amino acids containing polar uncharged side chain (AApusc) serine (Ser), threonine (Thr...

Colorimetric determination of cytosine-rich ssDNA by silver(I)-modulated glucose oxidase-catalyzed growth of gold nanoparticles.

A colorimetric assay is described for determination of cytosine-rich ssDNA at physiological pH values. The working principle is based on (a) Ag(I) ion-induced formation of an i-motif structure, and (b) glucose oxidase-controlled growth of gold nanoparticles (AuNPs). The combination between Ag+ and cytosine-rich DNA can modulate the generation of H2O2 resulting from enzyme catalyzed glucose oxidation. Depending on the amount of H2O2 formed, the solution containing the AuNPs will turn red in the presence of cytosine-rich ssDNA but blue in the absence of such DNA if Ag+ is added before the formation of the red AuNPs. Upon addition of C-DNA at different concentrations, the peak shift (Δλ) of the AuNP solution relative to the SPR peak position (560nm) in the absence of C-DNA is taken as the signal readout. The method shows a good linear response toward C-DNA over the range 10-200nM with a detection limit of 2.7nM. It may also be performed visually. The photometric assay is highly sensitive, specific, and rapid. The method is particularly attractive in terms of applications such as in human serum analysis, a colorimetric logic gate, and the calculation of binding constants for the interaction between Ag+ and glucose oxidase (GOx), and between Ag+ and cytosine-rich ssDNAs. Graphical abstract Schematic presentation of colorimetric detection of cytosine (C)-rich ssDNA (C-DNA) based on the modulation of the glucose oxidase (GOx)-catalyzed growth of gold nanoparticles (AuNPs) with Ag+ as the enzyme inhibitor.

Pulsed laser ablation in liquid assisted growth of gold nanoparticles: Evaluation of structural and optical features

High purity gold (Au) nanoparticles (NPs) with desired morphology are demanding for various applications. Being simple, versatile, and cost-effective technique, PLAL is promising for the production of impurities free nanoparticles (NPs) of diverse materials. This paper reports the preparation and characterization of colloidal Au-NPs. Such Au-NPs were produced via PLAL route, wherein the Au target was immersed inside deionized water and ablated using a Q-switched Nd:YAG laser (wavelength 1064 nm and pulse width 8 ns). The structural, morphological, and optical characteristics of the as-synthesized Au-NPs were evaluated as a function of varied laser energies and repetition rates. Optical traits of Au-NPs were analyzed by ultraviolet–visible (UV–Vis) absorption, photoluminescence, and Raman spectroscopy. Surface plasmon resonance (SPR) absorbance at the excitation wavelength of 633 nm was recorded to find the shape of the Au-NPs. Attenuated total reflection infrared (ATR-IR) spectra was obtained to verify the achieved Au-NPs purity. High-resolution transmission electron micrographs approved the nucleation of spherical colloidal Au-NPs (mean diameter of 7 to 30 nm) in deionized water. The UV–Vis spectra of Au-NPs disclosed the occurrences of SPR peaks in the range of 521 to 524 nm accompanied by blue-shift. The UV absorption edge of the UV–Vis spectra was used to determine the optical band gap energies of the produced Au-NPs which were further confirmed by the photoluminescence spectral analyses. Present findings based on PLAL-assisted synthesis of pure Au-NPs may be beneficial for the development photocatalysis and solar cells.

M13 phage as network frame for the quantification of Pb2+ based on the Pb2+-induced in-situ growth of gold nanoparticles

Routine detection of Pb2+ is of great importance to environmental monitoring because of its deleterious effects on human health and environment. In this work, an easy-to-operate method for the one-step detection of Pb2+ was developed based on the phage-Pb2+ interactions and their influence on the surface plasmon resonance (SPR) absorption band of AuNPs. AuNPs grow in-situ on the surface of M13 phages and the resulting phage-AuNP networks were directly used for lead sensing. The addition of Pb2+ facilitates further growth of the parent AuNPs and results in a blue shift of the SPR absorption peak. By integrating AuNPs preparation and sensing procedure into one step, a simplified Pb2+ detection approach was developed with improved sensitivity and shortened analysis time. By quantifying A528 with UV–vis spectrometer, a linear range of 0.5–5.0 μmol L−1 together with a limit of detection of 45 nmol L−1 was obtained. The one-step approach avoided complicated AuNPs preparation and functionalization process, and got rid of the unstable problems of AuNPs for long-term preservation, offering simple and cost-effective Pb2+ detection method for resource-poor settings.

Facile synthesis and dopamine sensing application of three component nanocomposite thin films based on polythiophene, gold nanoparticles and carbon nanotubes

A simple and versatile route to synthesize nanocomposite thin films containing polythiophene, gold nanoparticles and carbon nanotubes is demonstrated. The strategy is based on a liquid-liquid interfacial reaction, in which polythiophene and gold nanoparticles are concomitantly synthesized through a reaction between an aqueous solution of tetrachloroauric acid and a n-hexane solution of thiophene containing carbon nanotubes previously dispersed. The three-component nanocomposite is obtained directly as a thin and homogeneous film, self-assembled at the liquid-liquid interface, and easily transferable to ordinary substrates. Different reaction times were investigated, and the materials were characterized by several techniques, such as SEM, TEM, profilometry and EDS to inform about the morphology and the elementary composition, FTIR, Raman, TGA, UV–Vis and DRX about the structure of the materials and the electrochemical properties were investigated by cyclic voltammetry. The presence of carbon nanotubes accelerates the reaction, yielding greater amount of product when compared to similar reactions conducted without the carbon nanotubes. The proportion between the components, amount of products and film thickness can be controlled by the reaction time. It is observed that the amount of both polythiophene and gold nanoparticles increases with the increasing reaction time, inducing the formation of polymer agglomerates over de carbon nanotubes and the anisotropic growth of gold nanoparticles. The presence of CNT increases the electrochemical stability of the films when compared to similar ones without CNT. The potentiality of the prepared nanocomposite as electrochemical sensor was evaluated for voltammetric determination of dopamine. Best results were found for a PT/Au/CNT film prepared after 4.5h of reaction, with a limit of detection of 0.69μmolL−1.

Seeded growth of gold nanoparticles in aqueous solution of cationic gemini surfactants with different spacer length: influences of molecular and aggregate structures

It is well known that surfactants play a vital role in aqueous-phase synthesis of gold nanoparticles (GNPs). However, to date, it remains challenging to fully elucidate the roles of surfactants, especially for the correlation between the molecular and aggregate structure of the employed surfactant and the structures of the resulting GNPs. In the study, the synthesis of GNPs in aqueous solution of a series of cationic gemini surfactants with different spacer length (12-s-12, s = 0, 2, 4, 6, 8, 10, and 12) has been investigated. A remarkable spacer length-dependent morphological evolution of nanorod→nanostar→nanoplate→spherical nanoparticle has been observed. The results show that the gemini surfactants can form the electrostatic complexes with AuI ions, and the complexes further self-assemble into the various aggregates of different sizes, which greatly alters the migration dynamics of AuI and eventually influences the growth kinetics of GNPs. The overall growth rate of the GNPs is determined by the combination of the monomer-AuI molecular weight, the size of aggregates, and the local concentration of AuI in the aggregates. Besides, the gemini surfactants with different spacer length could selectively anchor on various facets of GNPs, thus acting as the capping agents to direct the formation of the shaped GNPs. It is believed that the cationic gemini surfactants with different spacer length provide an excellent choice to control the growth kinetics and final morphology of GNPs, and this study provides new insights in surfactant-assisted synthesis of GNPs.

Fabrication of non-destructive and enhanced electrochemiluminescence interface for reusable detection of cell-released dopamine

Quantification of cell-released dopamine (DA) is essential to understand various biological processes. However, concentration of DA outside living cells may increase and decrease in a short time. Thus, approaches used to detect cell-released DA should meet higher demands. Herein, a simple and green method is employed to in situ growth of gold nanoparticles on the surface of WS2 nanosheets. The defects of prepared Au-WS2 nanocomposites may accelerate electron transfer and facilitate the absorption of dissolved oxygen. As a result, Au-WS2 nanocomposites-enhanced electrochemiluminescence (ECL) is observed for the first time, and is further used to fabricate a non-destructive and label-free analytical interface. The ECL interface can selectively detect DA in a range of 5.0 nM–200 μM with a detection limit of 3.23 nM. Meanwhile, since the architecture on the ECL interface is not destroyed during the detection procedure, DA can be quantified continuously at least six times after one fabrication. In addition, the proposed ECL interface can accurately monitor the release of DA from PC12 cells manipulated by K+ and nifidipine, indicating great potential of this ECL sensor for surveying DA-related investigations.

In-situ growth of gold nanoparticles on a 3D-network consisting of a MoS2/rGO nanocomposite for simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid.

A glassy carbon electrode was modified with a 3D-networked nanostructure composed of MoS2, reduced graphene oxide and gold nanoparticles (3D-MoS2/rGO/Au). The composites were prepared through in-situ growth of gold nanoparticles on 3D-MoS2/rGO nanosheets via a hydrothermal method. The morphology and electrochemical features of the composite were investigated. The 3D-MoS2/rGO/Au sensor exhibits excellent electrocatalytic activity for simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The oxidation potentials are well separated at around -0.05V for AA, 0.06V for DA and 0.2V for UA, respectively. The detection limits for individual detection and simultaneous detection (S/N = 3) are 0.93μM and 1.46μM for AA, 0.11μM and 0.15μM for DA, and 0.74μM and 0.29μM for UA. The method was applied to the quantitative analysis of AA, DA, and UA in spiked serum samples with satisfying results. Graphical abstract In-situ growth of gold nanoparticles on 3D-networked MoS2/rGO nanocomposite for individual and simultaneous determination of ascorbic acid, dopamine and uric acid.

Growth of Gold Nanoparticles in a Glass Matrix by Continuous Laser Irradiation for Efficient Surface Enhanced Raman Scattering

The synthesis of a soda‐lime glass doped by gold nanoparticles (Nps) is achieved using successively thermal poling and continuous wave (cw) ultraviolet (UV) laser exposure. The formation of gold Nps is undoubtedly proved by an absorption band characteristic of their surface plasmon resonance (SPR), and by scanning electron microscopy, which reveals Nps of about 40 nm in diameter, located in the very near surface region of the glass. Absorption spectroscopy also suggests the formation of bimetallic silver‐gold Nps in systems prepared by using thermal poling and laser exposure of a glass previously doped by silver ions using ion exchange. Finally, the low detection limit of Rhodamine 6G (R6G) measured by surface‐enhanced Raman spectroscopy proves the potential of our gold‐doped glass as an efficient Raman substrate, which offers an alternative to silver Nps doped glass.

A seed-mediated growth of gold nanoparticles inside carbon nanotube fibers for fabrication of multifunctional nanohybrid fibers with enhanced mechanical and electrical properties.

The seed-mediated growth strategy of Au nanoparticles (Au NPs) inside carbon nanotube (CNT) fibers is demonstrated to greatly improve their mechanical and electrical properties and provide a function for catalytic applications. The resulting Au NP@CNT nanocomposite fibers exhibit 100% knot efficiency, catalytic activity and considerably enhanced modulus, tensile strength, and electrical conductivity from 7 GPa, 109 MPa and 1300 S cm-1 to 24 GPa, 351 MPa and 3600 S cm-1, respectively. The enhancement mechanism is also revealed by systematic characterization and theoretical simulations.

A Colorimetric Enzyme-Linked Immunosorbent Assay with CuO Nanoparticles as Signal Labels Based on the Growth of Gold Nanoparticles In Situ

A colorimetric immunoassay has been reported for prostate-specific antigen (PSA) detection with CuO nanoparticles (CuO NPs) as signal labels. The method is based on Cu2+-catalyzed oxidation of ascorbic acid (AA) by O2 to depress the formation of colored gold nanoparticles (AuNPs). Specifically, HAuCl4 can be reduced by AA to produce AuNPs in situ. In the presence of target, CuO NPs-labeled antibodies were captured via the sandwich-type immunoreaction. After dissolving CuO nanoparticles with acid, the released Cu2+ catalyzed the oxidation of AA by O2, thus depressing the generation of AuNPs. To demonstrate the accuracy of the colorimetric assay, the released Cu2+ was further determined by a fluorescence probe. The colorimetric immunoassay shows a linear relationship for PSA detection in the range of 0.1~10 ng/mL. The detection limit of 0.05 ng/mL is comparable to that obtained by other CuO NPs-based methods. The high throughput, simplicity, and sensitivity of the proposed colorimetric immunoassay exhibited good applicability for assays of serum samples.

Variable Growth and Characterizations of Monolayer-Protected Gold Nanoparticles Based on Molar Ratio of Gold and Capping Ligands.

Controlling the size of nanoscale entities is important because many properties of nanomaterials are directly related to the size of the particles. Gold nanoparticles represent classic materials and are of particular interest due to their potential application in a variety of fields. In this study, hexanethiol-capped gold nanoparticles are synthesized via the Brust-Schiffrin method. Synthesized nanoparticles were characterized by various analytical techniques such as transmission electron microscopy, scanning tunneling microscopy (STM), UV-visible absorption spectroscopy and electrochemical techniques. We have varied the molar ratio of gold to the protecting agent (hexanethiol) to discover the effect of gold-to-hexanethiol ligand ratio on the size of gold particles. The clear correlation between particle size and molar ratio is found that the averaged particle size decreases from 4.28 ± 0.83 to 1.54 ± 0.67 nm as the gold-to-ligand molar ratio changes from 1:1 to 1:9. In contrast to a recent report that thiolated gold nanoparticles are under spontaneous disintegration when they are assembled on a gold substrate, our STM experiments proved that these gold nanoparticles can form a stable monolayer or multiple layers on the platinum electrode without observing disintegration within 72 h. Therefore, our STM experiments demonstrate that the disintegration behavior of gold nanoparticles is related to the type of ligands and the nature of substrate materials. In electrochemical experiments, these gold nanoparticles displayed an electrochemical quantized charging effect, making these nanoparticles useful in the device applications such as electrochemical or biological sensors.

Promoting Effects of Iron on CO Oxidation over Au/TiO2 Supported Au Nanoparticles

Fe-doped TiO2 supported gold nanoparticles as high-performance CO oxidation catalysts were prepared. XRD data revealed that TiO2 support was in an anatase phase. After calcination at 300 °C, the sample showed nanotube structure, and the size of gold nanoparticles was 3.1 nm. When calcined at 500 °C, most nanotubes broke, and gold nanoparticles grew up to 5.9 nm. XPS spectrum indicated the presence of Fe in the +3 oxidation state. Au/Fe-TiO2(Au: 1.44%, Fe: 1.35%) calcined at 300 °C possessed the best catalytic activity, and it could completely convert CO at 25 °C. The temperature of 100% CO conversion(T100%) of Fe-free catalyst was 40 °C. After the catalysts were stored at room temperature for 7 d, T100% of Au/Fe-TiO2 increased from 25 °C to 30 °C, while T100% of Fe-free catalyst increased from 40 °C to 80 °C. The catalytic activity and storage stability of Au/TiO2 could be improved by Fe-doping. The increase of specific surface area, generation of oxygen vacancies and new adsorption sites, depression of the growth of gold nanoparticles, and strong metal-support interaction were responsible for the promoting effect of iron on the catalytic performance of Au/TiO2 for CO oxidation.

Formation of gold nanoparticles in a free-standing ionic liquid triggered by heat and electron irradiation

Ionic liquids (ILs) feature negligibly low vapor pressures and can thus be freely introduced into the high vacuum of a transmission electron microscope. With this extraordinary property, the ILs offer a powerful tool for in situ transmission electron microscopy (TEM) in window-free liquid media at very high resolution. In this work, we use the IL 1-butyl-3-methylimidazolium chloride in order to study nucleation and growth of gold nanoparticles (NPs) in free-standing liquid droplets by scanning TEM (STEM). The results confirm that the used IL allows for generating Au NPs in situ, triggered by electron irradiation and heat. Firstly, the isotropic growth of small, spherical Au NPs was initiated and monitored, whereas different growth mechanisms were observed, i.e. growth by monomer attachment, growth through particle coalescence and possible Ostwald ripening events. After the initial growth phase, a second, anisotropic growth process was induced by a moderate temperature increase and continued electron irradiation. As a result, larger, faceted crystals, such as tetrahedra, octahedra or decahedra, were formed. As all these polymorphs are terminated by {111}-facets, the IL might not only act as liquid medium but in addition as a surfactant which preferentially attaches on the {100}-facets.

Study of Growth of Bare and Protein-Modified Gold Nanoparticles in the Presence of Hydroxylamine and Tetrachloroaurate

Gold nanoparticles (GNPs) and their conjugates are widely used as labels in bioanalytical methods. One of the main characteristics that determine their unique plasmon properties is their size. In this work, the growth of bare and protein-modified (with streptavidin) GNPs in the presence of hydrogen tetrachloroaurate and hydroxylamine was studied. Three initial preparations of GNPs with average diameters of 30.5 ± 7.7, 19.2 ± 1.6, and 4.4 ± 0.6 nm were obtained. An increase in size of GNPs at different initial particle sizes, reagent concentrations, presence/absence of protein coating was characterized using the methods of optical spectrophotometry, dynamic laser light scattering and transmission electron microscopy. The presence of sorbed proteins was shown to reduce the growth rate and affect the morphology of the forming nanoparticles. The conditions (1–10 mM hydroxylamine, 30 mM hydrogen tetrachloroaurate) that ensure the maximum increase in the size of GNPs (up to ≈70 nm) and their conjugates in homogeneous systems without the formation of unstable aggregates were determined.

In Situ Growth and Size Regulation of Single Gold Nanoparticles in Composite Microgels.

Herein, a novel method for the in situ growth of single gold nanoparticles (AuNPs) in microgel (MG) networks is presented. The key feature in this approach is the localization of β-diketone groups capable of both complexation and reduction of aurate ions in the MGs' core, which allows localization of the nucleation and growth of single AuNPs. The MG synthesis is carried out via precipitation polymerization in water with N-vinylcaprolactam as the main monomer and with the two comonomers acetoacetoxyethyl methacrylate (AAEM) and acrylic acid (AAc), where AAEM is mainly located in the MGs' core and AAc in their shell. For the synthesis of AuNPs, a certain amount of chloroauric acid (HAuCl4 ) is added to the dispersion, followed by fast reduction with sodium borohydride (NaBH4 ). In situ synthesized AuNPs in MGs possess a spherical shape, with a diameter of 8.1 ± 0.8 nm, being localized in the center of every MG. In addition, these AuNPs embedded into MG networks can be used as seeds that grow in their size after the addition of HAuCl4 up to 46.0 ± 9.5 nm under mild reaction conditions (room temperature, aqueous dispersion) and without the use of any additional reducing and stabilizing agents.

Post-assay growth of gold nanoparticles as a tool for highly sensitive lateral flow immunoassay. Application to the detection of potato virus X.

This article demonstrates a new kind of a highly sensitive lateral flow immunoassay (LFIA). It is based on the enlargement of the size of gold nanoparticles (GNPs) directly on the test strip after a conventional LFIA. Particle size enlargement is accomplished through the catalytic reduction of HAuCl4 in the presence of H2O2 and through the accumulation of additional gold on the surface of the GNPs. To attain maximal enhancement of the coloration of the zone in the test strip and toachieve a minimal background, the concentration of precursors, the pH value, and the incubation time were optimized. GNPs on the test strip are enlarged from 20 to 350nm after a1-min treatment at room temperature. The economically important and widespread phytopathogen potato virus X (PVX) was used as the target analyte. The use of the GNP enlargement method results in a 240-fold reduction in the limit of the detection of PVX, which can be as low as 17pg·mL-1. The total duration of the assay, including virus extraction from the potato leaves, lateral flow, and the enhancement process, is only 12min. The diagnostic efficiency of the technique was confirmed by its application to the analysis of potato leave samples. No false positives or false negatives were found. The technique does not depend on specific features of the target analyte, and it is conceivablyapplicable to numerous GNP-based LFIAs for important analytes. Graphical abstract An enlargement solution (containing HAuCl4 and H2O2) was dripped on the strip after common lateral flow immunoassay. Gold nanoparticles on the strip (20nm) catalyze gold reduction and the formation of larger particles (up to 350nm), resulting in a 240-fold lower detection limit within 1min.