3D Gold Research Articles

Three-dimensional gold micro-/nanopore arrays containing 2-mercaptobenzothiazole molecular adapters allow sensitive and selective stripping voltammetric determination of trace mercury (II)

Three-dimensional (3D) gold micro-/nanopore arrays containing 2-mercaptobenzothiazole (MBT) adapters have been prepared and employed to improve the performance of the determination of trace mercury in solution using square wave anodic stripping voltammetry (SWASV). 3D gold micro-/nanopore arrays have an active surface area which is up to 4 and 15 times higher than a two-dimensional (2D) bowl-like structured microarrays and a flat solid gold electrode characterized by cyclic voltammetry, respectively. In this study, 3D MBT molecular adapters on the array surface greatly decreased the effect of capacitive current and enhanced the sensitivity and selectivity of the electrode. A limit of detection of 0.02 nM (which is well below the guideline given by the World Health Organization) and more importantly, a sensitivity of 1.85 μA nM −1 was obtained using this system. Furthermore, excellent linear range (0.05–10 nM) and good repeatability (relative standard deviation of 2.10%) were obtained for Hg(II). Interference experiments were also investigated, and it was determined that Pb(II), Cd(II), Zn(II), Cu(II) and Ag(I) had little or no influence on the mercury signal.

Trace detection of picloram using an electrochemical immunosensor based on three-dimensional gold nanoclusters

Picloram, a herbicide widely used for broadleaf weed control, is persistent and mobile in soil and water with adverse health and environmental effects. It is important to develop a sensitive method for accurate detection of trace picloram in the environment. In this article, a type of ordered three-dimensional (3D) gold (Au) nanoclusters obtained by two-step electrodeposition using the spatial obstruction/direction of the polycarbonate membrane is reported. Bovine serum albumin (BSA)–picloram was immobilized on the 3D Au nanoclusters by self-assembly, and then competitive immunoreaction with picloram antibody and target picloram was executed. The horseradish peroxidase (HRP)-labeled secondary antibody was applied for enzyme-amplified amperometric measurement. The electrodeposited Au nanoclusters built direct electrical contact and immobilization interface with protein molecules without postmodification and positioning. Under the optimal conditions, the linear range for picloram determination was 0.001–10 μg/ml with a correlation coefficient of 0.996. The detection and quantification limits were 5.0 × 10 −4 and 0.0021 μg/ml, respectively. Picloram concentrations in peach and excess sludge supernatant extracts were tested by the proposed immunosensor, which exhibited good precision, sensitivity, selectivity, and storage stability.

Layer-by-Layer Assembly of Three-Dimensional Colloidal Supercrystals with Tunable Plasmonic Properties

We present a simple and efficient method for synthesizing large-area (>1 cm(2)), three-dimensional (3D) gold and silver nanoparticle supercrystal films. In this approach, Janus nanoparticle (top face solvent-phobic and bottom face solvent-philic) films with an arbitrary number of close-packed nanoparticle monolayers can be formed using layer-by-layer (LbL) assembly from suspensions of thiolate-passivated gold or silver colloids. Furthermore, we demonstrate that these films can act as true 3D plasmonic crystals with strong transverse (intralayer) and longitudinal (interlayer) near-field coupling. In contrast to conventional polyelectrolyte-mediated LbL assembly processes, this approach allows multiple longitudinal coupling modes with a conspicuous spectral dependence on the layer number. We have found a universal scaling relation between the spectral position of the reflectance dips related to the longitudinal modes and the layer number. This relation can be understood in terms of the presence of a plasmonic Fabry-Perot nanocavity along the longitudinal direction that allows the formation of standing plasmon waves under plasmon resonance conditions. The realization of 3D plasmonic coupling enables broadband tuning of the collective plasmon response over a wide spectral range (visible and near-IR) and provides a pathway to designer plasmonic metamaterials.

Enzymatic synthesis of gold nanoflowers with trypsin

A one-step and eco-friendly approach for the room-temperature synthesis of trypsin-mediatedthree-dimensional (3D) gold nanoflowers (AuNFs) with high colloidal stability is demonstrated.To prepare AuNFs, ascorbic acid (AA) was quickly added into the premixed solution ofHAuCl4 andtrypsin at pH = 5.0. The results show that the molar ratio and feeding order of reactant agents,pH and reaction time play important roles in the formation of NFs. Thegrowth mechanism of AuNFs is suggested as three steps: (1) immobilization ofAuCl4 − ions with a positively charged trypsin template, (2) spontaneous reduction ofAuCl4 − ions with AA in situand capping Au0 by 12 cysteines of trypsin, (3) reduction of moreAuCl4 − ions on the Au nuclei formed in the initial stages and anisotropic growth into AuNFs.

Uniform Surface Patterning with Two-Dimensional Gold Nanoparticle Array Excited by Oblique Femtosecond Laser Irradiation

We present optical field distributions and nanohole patterning properties on a silicon substrate when a femtosecond laser is irradiated obliquely to a two-dimensional (2D) gold nanoparticle array on a silicon surface. It is necessary to control plasmon polaritons in a gold nanoparticle array by adjusting interparticle distance and the incident angle of the laser for uniform nanohole patterning with an 800 nm femtosecond laser. The uniform 2D nanohole patterning is studied by finite-difference time-domain (FDTD) calculation and experiment using a femtosecond laser. Using an array with gold particles of 200 nm diameter, the near-field intensity on the Si surface is much larger than that of a single isolated particle if the interparticle distance is larger than 200 nm and the incident angle is approximately 50°. The oblique irradiation of p-polarized incident laser to the surface of the substrate ensures that uniform nanohole array patterning is achieved.

Immobilization of acetylcholinesterase on one-dimensional gold nanoparticles for detection of organophosphorous insecticides

This paper reports a simple method for immobilization of acetylcholinesterase (AChE) on one-dimensional (1D) gold (Au) nanoparticles for detection of organophosphorous (OP) insecticides. 1D Au nanoparticles were prepared by electrodeposition in the pores of an alumina template which was subsequently removed by 2.0 M NaOH solution. They were characterized by XRD and FESEM. The immobilized AChE retained its biological activity and catalyzed the hydrolysis of acetylthiocholine to form thiocholine, which was subsequently oxidized to produce detectable signals. Based on the inhibition toward the enzymatic activity of AChE by OP insecticides, sensitive detection of methamidophos (an OP insecticide) was performed. Under optimal conditions, the sensors could be used for the determination of methamidophos ranging from 0.004 to 24 μg/mL with the detection limit of 0.001 μg/mL. The developed OP insecticide biosensors exhibited satisfactory stability and reproducibility. This work demonstrated that 1D Au nanoparticles could serve as an ideal carrier for immobilization of AChE to fabricate the corresponding biosensor.

Facile fabrication of 3D dendritic gold nanostructures with an AuSn alloy by square wave potential pulse

Multifunctional three dimensional (3D) dendritic gold (DG) nanostructures have been synthesized facilely by square wave potential pulse (SWPP) with an Au 45Sn 55 (wt.%) alloy in an electrolyte of NaOH or H 2SO 4. The dendrite formation involves combined actions of selective removal of Sn, oxidation–reduction cycles (ORCs) of gold and intensive hydrogen evolution, wherein the nanopores from dealloying and the movement of hydrogen bubbles facilitate the dendrite formation by rearranging the newly produced Au atoms from the ORCs. An alkaline medium is preferable and the dendritic structure can be obtained as quickly as in 100 s. Some applications have been demonstrated with the prepared DG including electrocatalytic oxidation of glucose, surface-enhanced Raman scattering, and superhydrophobicity.

CO2-responsive TX-100 emulsion for selective synthesis of 1D or 3D gold

The effect of CO2 on the properties of water/poly(oxyethylene)iso-octylphenyl ether (TX-100)/isooctane emulsions was investigated by direct observation, small angle X-ray scattering (SAXS), and UV-vis spectroscopy at 303.2 K in the pressure range 0–5 MPa. It was demonstrated that the droplet size of the emulsion was sensitive to the pressure of CO2, and the droplet size can be tuned in a wide range from the micron to the nanometre scale. When the CO2 pressure was 3.90 MPa, the droplet size reached a minimum value of 92 nm. To demonstrate the utilization of the CO2-responsive water/TX-100/isooctane emulsion, gold particles were synthesized using HAuCl4 as a gold precursor and TX-100 as a reducing reagent. It was shown that gold particles with different morphologies, such as nanowires, nanorods, and polyhedral nanocrystals could be synthesized by controlling the pressure of CO2.

3D dendritic gold nanostructures: seeded growth of a multi-generation fractal architecture

In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

Direct electrochemistry of horseradish peroxidase immobilized on a monolayer modified nanowire array electrode

Vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three-dimensional (3D) matrix for immobilization of redox proteins. Third-generation H 2O 2 biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5 h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE 5 h (5 h deposition time) exhibited remarkable sensitivity (45.86 μA mM −1 cm −2) towards H 2O 2 with a detection limit of 0.42 μM ( S/ N = 3), linearity up to 15 mM and a response time of 4 s. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.

Squeezing light into subwavelength metallic tapers: single mode matching method

A simple single mode matching (SMM) method is proposed to analyze the optical throughput for subwavelength metal tapers. Both a 2D gold-clad taper gap and a 3D gold taper rod are analyzed with the SMM method. Including metal losses, these structures are calculated to have optimal squeezing taper angles of 14° with 71% efficiency and 32° with 44% efficiency, which is in good quantitative agreement with previous finite-difference time-domain simulations. The SMM method uses only analytic calculations and 2-by-2 matrix multiplication. Therefore, compared to past approaches, the SMM method is an efficient method to optimize the subwavelength metallic taper structures, while including losses, and it can be extended to more complex tapers and gratings in an obvious way. It also has the potential for fully analytic calculations.

CO Adsorption on One-, Two-, and Three-Dimensional Au Clusters Supported on MgO/Ag(001) Ultrathin Films

The adsorption properties of CO molecules adsorbed on free and MgO supported Au clusters have been investigated by means of a first principles density functional theory (DFT) approach. We have focused our attention on the vibrational properties of CO adsorbed on gas-phase Au3−7, Au12, and Au22 cluster anions, and on Au3−5, Au12, and Au22 clusters deposited on MgO/Ag(001) films or on the bare MgO(001) surface. We also considered a full gold monolayer deposited on MgO/Ag(001). CO does not bind to the high-coordinated Au atoms of one- or two-dimensional (1D or 2D) gold clusters or islands but only to the low-coordinated atoms at the periphery of these structures. A red-shift of about 50−60 cm−1 is found in ω(CO) for gold clusters deposited on MgO/Ag(001) thin films compared to the same clusters deposited on bare MgO(001) or to the neutral gas-phase counterparts. This shift, due to the occurrence of a charge transfer from the metal support to the deposited gold cluster, is found only for small 1D or 2D cluste...

Amperometric biosensor for hydrogen peroxide and nitrite based on hemoglobin immobilized on one-dimensional gold nanoparticle

Hemoglobin (Hb) was immobilized on one-dimensional (1D) gold (Au) nanoparticles to construct a novel amperometric biosensor for hydrogen peroxide (H 2O 2) and nitrite (NO 2 −). 1D Au nanoparticles were prepared by electrodepositon in the pores of an alumina template and were characterized by XRD and TEM. The immobilized Hb retained its biological activity well and displayed a good response to the reduction of both H 2O 2 and NO 2 −. Its apparent Michaelis–Menten constants for H 2O 2 and NO 2 − were 10.8 and 35.3 μM, respectively, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H 2O 2 ranging from 0.6 to 12.4 μM and NO 2 − ranging from 0.4 to 14.8 μM. The detection limits were 2.4 × 10 −8 and 6.5 × 10 −8 M at 3σ, respectively. 1D Au nanoparticles provided a good matrix for protein immobilization and biosensor preparation.

Atomic Oxygen Adsorption on Au(111) Surfaces with Defects

We study the equilibrium structures for the adsorption of atomic oxygen on Au(111) surfaces containing defects such as vacancies and steps, using first-principles density functional theory calculations. We considered the gold−oxygen interaction as a function of surface vacancy concentration, the interaction with 1,2 and 4 gold adatoms (the latter number arranged in groups that represent 2D or 3D gold islands), the interaction at steps, and finally, the effect of strain. We find that there is an attractive interaction between oxygen atoms and vacancies on the surface, which lowers the cost to create a surface vacancy by 0.20 eV, but the interaction between oxygen and gold adatoms is repulsive. We conclude that the strength of the oxygen−gold interaction is correlated with the coordination number of the gold atom to which the oxygen is bound.

Characteristics of surface-enhanced Raman scattering and surface-enhanced fluorescence using a single and a double layer gold nanostructure

This paper reports the characteristics of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) using a unique SERS-active substrate comprised of a single layer and a double layer of two-dimensional (2D) gold nanostructure. Colloidal gold nanoparticles were immobilized on a glass substrate and a multi-purpose experimental setup was adopted to obtain surface plasmon resonance (SPR), SERS and SEF on a single platform. Inhomogeneous intensity distribution was observed in correlated images of SPR and SERS. Several laser lines were used as excitation sources for further SERS measurements. Higher SERS intensities were observed with longer wavelength excitations at the same spatial position. Fluorescence measurements were carried out using 514 nm line and SEF images were obtained using the same sample. Fluorescence emissions were found to be enhanced in the presence of 2D gold nanostructure. A series of SERS spectra were recorded by conducting ensemble SERS measurements at a periodic interval of 2 microm, crossing bare substrates, the single layer and the double layer of gold nanostructure. The double layer provides higher enhancement in SERS than that of the single layer. Polarization-selective SERS measurements obtained at the single layer and double layer showed a clear difference in their dispersions. SERS intensities of the analytes adsorbed at the single layer were fitted well with cos(4)theta dependence; however, for the double layer, the relationship was quite uncertain.

Self-organization of an organic–inorganic hybrid nanomushroom by a simple synthetic route at the organic/water interface

A new strategy for the synthesis of a mushroom-like aggregate, based on repeated sequences of a 3D gold nanoparticle-conducting polymer-gold nanoparticle arrangement, by a single-step process at the organic/water interface has been described.

Metallic Cation Induced One-Dimensional Assembly of Poly(acrylic acid)−1-Dodecanethiol-Stabilized Gold Nanoparticles

In this work, we report a simple approach for controllable synthesis of one-dimensional (1D) gold nanoparticle (AuNP) assemblies in solution. In the presence of divalent metallic ions, poly(acrylic acid)-1-dodecanethiol-stabilized AuNPs (PAA-DDT@AuNPs) are found to form 1D assemblies in aqueous solution by an ion-templated chelation process; this causes an easily measurable change in the absorption spectrum of the particles. The assemblies are very stable and remain suspended in solution for more than one month without significant aggregation. The morphologies of these 1D assemblies are dependent on the concentration of metallic cations in the solution. While lower concentrations led to the formation of particle dimers, higher concentrations generated long nanoparticle chain networks. In addition, the effect of EDTA, the solution pH, and the size of the PAA-DDT@AuNPs is also studied for further exploration of the mechanism of the formation of the 1D assemblies.

Tailor-made gold brush nanoelectrode ensembles modified with l-cysteine for the detection of daunorubicine

A new functionalized l-cysteine surface modified 3D gold brush nanoelectrode assembly BNEE ( l-cys/BNEEs) was prepared. The BNEEs consisted of gold nanowires 100 nm in diameter and up to 400 nm in length fabricated by template synthesis in track etched polycarbonate membranes. The nanowires were exposed by controlled chemical etching of the membrane and were then modified by coating l-cys on the surface of the exposed gold nanowires. The morphology of the BNEEs was imaged by scanning electron microscopy and the real active area of BNEEs was determined by electrochemical impedance spectroscopy. The redox of daunorubicine (DNR) at the l-cys/BNEEs exhibited absorption-controlled characteristics and higher current activity than that at l-cys surface modified 2D disk NEEs ( l-cys/DNEEs). The square wave voltammetry technique was employed to detect DNR. The detection limit was 1.0 × 10 −8 M (s/n = 3). The linear detection concentration range of DNR was from 2.5 × 10 −8 to 4.0 × 10 −7 M.

Wires, Plates, Flowers, Needles, and Core−Shells: Diverse Nanostructures of Gold Using Polyaniline Templates

A simple and versatile method for the synthesis of a wide range of polyaniline (PANI)-based 1D and 2D gold nanostructures of uniform size distribution with high colloidal stability is demonstrated. All the nanostructures were synthesized from oligoaniline-coated gold nanoparticle precursors. The nanostructures include nanowires of various sizes, nanoplates, and flower-like nanoparticles. These nanowires showed a pH-dependent shape transformation. Needle-like aggregates of Au/PANI were formed as the pH of the nanowire solution changed to 2.5. At higher pH (10.2), nanowires converted into spherical nanoparticles. Core-shell particles of Au/PANI composites have been achieved by the reversal of the pH of the nanowire from 10.2 to 2.9. The morphology of the nanostructures was studied by TEM and SEM. FTIR, UV-vis, XRD, and LDI MS were utilized for the characterization of the chemical composition of the nanostructures. A mechanism for the nanowire growth is proposed.

Polymer-Templated Self-Assembly of a 2-Dimensional Gold Nanoparticle Network

We here report on the formation of well-ordered 2D gold nanostructures at the air/water interface. Spreading a mixture of alkanethiol-capped gold nanoparticles (AuNPs) and an amphiphilic poly(p-phenylene) on a water surface and compressing the mixture to a surface pressure of 40 mN/m lead to the formation of a network of well-ordered gold nanostructures. The structures are transferred horizontally (Langmuir-Schäfer) onto a solid substrate and investigated with TEM, AFM, and X-ray reflectivity, showing a pattern that is repeating over several micrometers. AFM and X-ray reflectivity data at different surface pressures reveal that the polymer is lifting the AuNPs 1.5-2 nm in the vertical direction, away from the polymer layer, when the pressure is increased from 20 to 40 mN/m.