3D Gold Research Articles

Terasonic Excitations in 2D Gold Nanoparticle Arrays in a Water Matrix as Revealed by Atomistic Simulations

In this work we report on terahertz phononic excitations in two-dimensional (2D) gold nanoparticle arrays in a water matrix through a series of large-scale molecular dynamics simulations. For the first time, we observe acoustic Dirac-like crossings in H (H2O) atomic (molecular) networks that emerge due to an intraband phononic scattering. These crossings are the phononic fingerprints of ice-like arrangements of H (H2O) atomic (molecular) networks at nanometer scale. We reveal how phononic excitations in metallic nanoparticles and the water matrix reciprocally impact on one another providing the mechanism for the THz phononics manipulation via structural engineering. Furthermore, we show that by tuning the arrangement of 2D gold nanoparticle assemblies, the Au phononic polarizations experience subterahertz hybridization (Kohn anomaly) due to surface electron–phonon relaxation processes. This opens the way for the sound control and manipulation in soft matter metamaterials at nanoscale.

3D nanoporous gold scaffold supported on graphene paper: Freestanding and flexible electrode with high loading of ultrafine PtCo alloy nanoparticles for electrochemical glucose sensing

Recent advances in on-body wearable medical apparatus and implantable devices drive the development of light-weight and bendable electrochemical sensors, which require the design of high-performance flexible electrode system. In this work, we reported a new type of freestanding and flexible electrode based on graphene paper (GP) supported 3D monolithic nanoporous gold (NPG) scaffold (NPG/GP), which was further modified by a layer of highly dense, well dispersed and ultrafine binary PtCo alloy nanoparticles via a facile and effective ultrasonic electrodeposition method. Our results demonstrated that benefited from the synergistic effect of the electrocatalytically active PtCo alloy nanoparticles, the large-active-area and highly conductive 3D NPG scaffold, and the mechanically strong and stable GP electrode substrate, the resultant PtCo alloy nanoparticles modified NPG/GP (PtCo/NPG/GP) exhibited high mechanical strength and good electrochemical sensing performances toward nonenzymatic detection of glucose, including a wide linear range from 35 μM– to 30 mM, a low detection limit of 5 μM (S/N = 3) and a high sensitivity of 7.84 μA cm−2 mM−1 as well as good selectivity, long-term stability and reproducibility. The practical application of the proposed PtCo/NPG/GP has also been demonstrated in in vitro detection of blood glucose in real clinic samples.

Three-dimensional gold nanoparticles/prussian blue-poly(3,4-ethylenedioxythiophene) nanocomposite as novel redox matrix for label-free electrochemical immunoassay of carcinoembryonic antigen

We present a novel label-free electrochemical immunosensor for detecting carcinoembryonic antigen (CEA) based on three-dimensional (3D) gold nanoparticles/prussian blue-poly(3,4-ethylenedioxythiophene) (AuNPs/PB-PEDOT) nanocomposite, which was firstly synthesized by a simple redox reaction between the PB precursors and EDOT in an aqueous solution, followed by the electrochemical reduction of HAuCl4. The 3D nanocomposite not only possessed large surface area and favorable microenvironment, but also exhibited remarkable conductivity, stability and excellent biocompatibility. In addition, PB showed excellent redox properties. Then AuNPs/PB-PEDOT was used as both electron mediators and 3D matrices in the fabrication of immunosensor. FT-IR spectra were employed to confirm the formation of PB, PEDOT and PB-PEDOT. Significantly, the AuNPs/PB-PEDOT exhibited a 3D and hierarchically porous nanostructure, while the PB-PEDOT showed core-shell structure. The AuNPs/PB-PEDOT modified immunosensor showed good linearity with the concentration of CEA ranging from 0.05 to 40ngmL−1, and the detection limit was 0.01ngmL−1. Moreover, the prepared electrode displayed good selectivity, high stability and good repeatability, and showed great potential for application in real sample analysis.

Near perfect light trapping in a 2D gold nanotrench grating at oblique angles of incidence and its application for sensing

A two-dimensional nanotrench cavity grating on a thick gold film was fabricated by using e-beam lithography. Optical reflection spectra from the fabricated device were measured at oblique angles of incidence for TE and TM polarizations. Near perfect light absorption was observed at different wavelengths for TE and TM polarizations at oblique angles of incidence. The peak absorption wavelength of TM polarization red-shifts significantly as angle of incidence increases. The peak absorption wavelength of TE polarization blue-shifts slightly as incident angle increases. Using finite-difference time-domain (FDTD) simulations, two orders of magnitude magnetic field enhancement was revealed inside nanotrenches, indicating strong light trapping inside the nanostructure. The fabricated device was investigated as a refractive index chemical sensor. It was found that sensitivity increases for TM polarization and decreases for TE polarization when angle of incidence increases from zero.

Formation and Self-assembly of Gold Nanoplates through an Interfacial Reaction for Surface-Enhanced Raman Scattering.

3D hierarchical architectures assembled from individual particles have attracted great interest because they displayed novel properties from the individual building blocks as well as their complex structures. Here we present a new strategy to form 3D hierarchical gold (Au) nanostructures via an interfacial reduction reaction. An aniline (ANI) derivative, N-(3-amidino)-aniline (NAAN), and HAuCl4 were separately dissolved in toluene and water to form an organic/water interface. Au nanoplates formed at the interface and subsequently moved to the aqueous phase. As a capping agent for the nanoplate formation, the oxidized NAAN, i.e., poly(N-(3-amidino)-aniline) (PNAAN), also facilitated the self-assembly of Au nanoplates into 3D hierarchical Au nanoflowers (AuNFs) through π-π stacking. The individual AuNF exhibited good surface-enhanced Raman scattering (SERS) response both in enhancement factor and reproducibility because it integrates the SERS enhancement effects of individual Au nanoplates and their hierarchical structures. This is the first report depicting the one-pot formation and self-assembly of Au nanoplates into 3D organized hierarchical nanostructures through the molecular interaction of conducting polymer.

Unraveling the electrical conduction of C-40 quasi-fullerene molecular junction

In this paper, we present the state of art theoretical calculations of charge transport through quasi-fullerene molecule C40 coupled rigidly between two 3D gold electrodes by applying different electro-chemical potentials. The methodology we adopted has been based on density functional theory approach combined with Keldysh’s non-equilibrium Green’s function (NEGF) framework suggested for mesoscopic systems. The results exhibited by this molecular junction confirmed it to be highly metallic and showed prominent conduction of the order of twice of the quantum conductance, i.e., 2*G[Formula: see text] at zero bias. Our results are consistent with theoretical predictions in ab initiocalculations with some variants of quasi-fullerenes.

Directional surface enhanced Raman scattering on gold nano-gratings

Directional plasmon excitation and surface enhanced Raman scattering (SERS) emission were demonstrated for 1D and 2D gold nanostructure arrays deposited on a flat gold layer. The extinction spectrum of both arrays exhibits intense resonance bands that are redshifted when the incident angle is increased. Systematic extinction analysis of different grating periods revealed that this band can be assigned to a propagated surface plasmon of the flat gold surface that fulfills the Bragg condition of the arrays (Bragg mode). Directional SERS measurements demonstrated that the SERS intensity can be improved by one order of magnitude when the Bragg mode positions are matched with either the excitation or the Raman wavelengths. Hybridized numerical calculations with the finite element method and Fourier modal method also proved the presence of the Bragg mode plasmon and illustrated that the enhanced electric field of the Bragg mode is particularly localized on the nanostructures regardless of their size.

Study of gold nanostructures of various dimensions: Au NWs, Au nanosheets, Au nanocylinders

Using atomistic simulations, we study the impact of stretching on the structural evolution of 1D monatomic gold nanochains (MACs) undergoing elongation using SIESTA (Spanish Initiative for Electronic Simulation with Thousands of Atoms), the computational code based on DFT. Further we extend our work to the study of 2D gold nanosheets and 3D gold nanocylinders. Since the study of stretching of gold nanosheets and nanocylinders using DFT is computationally demanding, we will be using many body Gupta Potential.It will be seen that during the stretching of nanosheets different defects will arise while stretching of gold nanocylinders leads to gold monoatomic chain formation.

Magnetically tunable colloidal micromirrors.

Herein we demonstrate a method for decorating highly reflective 2D gold microplates with magnetic nanoparticles to produce an optical colloid that can be actuated using an applied magnetic field. These magnetic micromirrors can be rapidly rotated and exhibit a strong contrast in reflectance between the "on" and "off" states.

Bridging model and real catalysts: general discussion.

Charles Campbell opened the discussion of the paper by Hans-JoachimFreund: If you have a 3D gold particle and it spreads out to be a 2D particle whenyou adsorb CO2, it must gain energy stability. Did you estimate the energy changeof the overall process to do that?

Visualizing Under-Coordinated Surface Atoms on 3D Nanoporous Gold Catalysts.

The intricate 3D geometric shape and surface atomic structure of nanoporous gold catalysts are investigated using aberration-corrected scanning transmission electron microscopy in combination with discrete tomography. The real-space 3D atomic configurations illustrate geometrically necessary surface defects on the curved surface of the NPG, offering atomic insights into the catalysis of the nanoporous catalyst.

Portable kit for identification and detection of drugs in human urine using surface-enhanced Raman spectroscopy.

A portable kit was demonstrated for rapid and reliable surface-enhanced Raman scattering (SERS) detection of drugs in human urine. This kit contains two sealed reagent tubes, a packet of standardized SERS substrates, and a mini Raman device. A 3 min pretreatment for separating amphetamines from human urine was developed with an extraction rate of >80% examined by ultraperformance liquid chromatography (UPLC). Simultaneously, highly reproducible two-dimensional (2D) gold nanorod (GNR) arrays were assembled by the use of methoxymercaptopoly(ethylene glycol) (mPEG-SH) capping. Thirty batches of GNR arrays produced the 1001 cm(-1) intensity of methamphetamine (MA) molecules with a relative standard deviation (RSD) of 7.9%, and a 21 × 21 μm(2) area mapping on a 2D GNR array produced a statistical RSD of <10%, implying an excellent reproducibility and uniformity. The detection limit of amphetamines in human urine was at least 0.1 ppm. Moreover, the portable kit was successfully used for detecting MA, 3,4-methylenedioxymethamphetamine (MDMA), and methcathinone (MC) in 30 volunteers' urine samples with various clinical natures, and the dual-analyte detection of MA and MDMA implied a good capability of multiplex analysis. UPLC examination and the SERS recovery test clearly indicated that our pretreatment procedure was sufficient to lower the high background signals caused by complex components in urine and demonstrated the practicability and the resistance to false positives, which is a vital problem for law enforcement applications. The excellent performance of our portable kit promises a great prospective toward a rapid, reliable, and on-spot analyzer, especially for public safety and healthcare.

Label-free piezoelectric immunosensor decorated with gold nanoparticles: Kinetic analysis and biosensing application

A label-free electrochemical quartz crystal microbalance (EQCM) based immunosensor using self-assembled monolayer of hexandithiol (HDT), cysteamine and 3D gold nanoparticles (AuNPs) was fabricated and utilized for aflatoxin B1 (AFB1, food mycotoxin) detection. The morphology, bonding and optimized experimental conditions of fabricated electrode and immunoelectrode were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR) and electrochemical quartz crystal microbalance cyclic voltammetry (EQCM-CV) techniques. This novel Cys/AuNPs/HDT/Au platform was utilized for covalent immobilization of aAFB1. The two linear ranges are observed under optimized experimental conditions i.e. 0.008–0.3ngmL−1 and 1–10ngmL−1 that can be used to estimate AFB1 with high sensitivity of 126μAng−1mLcm−2 and low detection limit of 8pgmL−1 using EQCM-CV. The label free AFB1 detection in noncompetitive mode with high sensitivity and wide linear range is assigned to the presence of antibodies and networking of 3D AuNPs on self assembled HDT monolayer. Attempts have also been made to utilize the immnunosensor for detection of AFB1 in spiked corn flakes samples for validating the observed results.

Super-radiant plasmon mode is more efficient for SERS than the sub-radiant mode in highly packed 2D gold nanocube arrays.

The field coupling in highly packed plasmonic nanoparticle arrays is not localized due to the energy transport via the sub-radiant plasmon modes, which is formed in addition to the regular super-radiant plasmon mode. Unlike the sub-radiant mode, the plasmon field of the super-radiant mode cannot extend over long distances since it decays radiatively with a shorter lifetime. The coupling of the plasmon fields of gold nanocubes (AuNCs) when organized into highly packed 2D arrays was examined experimentally. Multiple plasmon resonance optical peaks are observed for the AuNC arrays and are compared to those calculated using the discrete dipole approximation. The calculated electromagnetic plasmon fields of the arrays displayed high field intensity for the nanocubes located in the center of the arrays for the lower energy super-radiant mode, while the higher energy sub-radiant plasmon mode displayed high field intensity at the edges of the arrays. The Raman signal enhancement by the super-radiant plasmon mode was found to be one hundred fold greater than that by sub-radiant plasmon mode because the super-radiant mode has higher scattering and stronger plasmon field intensity relative to the sub-radiant mode.

Phosphonate-functionalized three-dimensional gold nanocomposite as a sensitive interface for facile electrochemical stripping detection of trace copper(II) ions

In biological systems, specific status of the essential transition metal ions in body fluids is of clinical significance for sustaining normal, healthy individual. In this work, we demonstrate an efficient and controllable phosphonate-functionalized interface, self-assembled on the surface of three-dimensional nanoporous gold electrode, that responds to trace copper(II) ions in aqueous solution with appropriate sensitivity and stability, when combined with facile differential pulse anodic stripping voltammetry (DPASV), thus offering the opportunity to probe physiological and pathological condition of cellular metals with spatial fidelity. The structural morphology and electrochemical properties of the as-prepared phosphonate-functionalized three-dimensional (3D) gold electrodes were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), dynamic contact angle analysis and cyclic voltammetry. The results indicated that, by use of cost-effective materials of short-chain MPPA (3-mercaptopropylphosphonic acid), the derived less densely packed self-assembled monolayers (SAMs), with evenly-spread terminal –PO3H2 functionality at intermediate surface coverage unlike its long-chain counterparts, exhibited great performance for trace analysis of heavy metal ions of copper(II) in aqueous environment. Incorporated with 3D gold substrate, possessing highly interconnected hierarchical porous structure beneficial for mass transport, a linear dynamic range from 0.05 to 350μM to the detection of copper ions, was obtained under the optimized conditions with a relatively low detection limits. The proposed sensing interface using phosphonic moieties as functional group holds promise to generally estimate metal accumulation, trafficking, and function or toxicity in living systems.

Octahedral and Cubic Gold Nanoframes with Platinum Framework.

Herein, we report a general synthetic pathway to various shapes of three-dimensional (3D) gold nanoframes (NFs) embedded with a Pt skeleton for structural rigidity. The synthetic route comprises three steps: site-specific (edge and vertex) deposition of Pt, etching of inner Au, and regrowth of Au on the Pt framework. Site-specific reduction of Pt on Au nanoparticles (NPs) led to the high-quality of 3D Au NFs with good structural rigidity, which allowed the detailed characterization of the corresponding 3D metal NFs. The synthetic method described here will open new avenues toward many new kinds of 3D metal NFs.

Two-dimensional gold nanostructures with high activity for selective oxidation of carbon-hydrogen bonds.

Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold–gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon–hydrogen bonds with molecular oxygen.

Rapid Fabrication of Gold Nanoflowers Tuned by pH: Insights Into the Growth Mechanism.

We reported a one-pot, no added seeding and green method to synthesize gold nanoflowers, in which HAuC4 and H2O2 were added one by one into the alkaline protocatechuic aldehyde solution at room temperature. Au(III) was partially reduced by protocatechuic aldehyde to produce primary Au nanocrystals, and then Au nanocrystals agglomerated into loose flower-like nanoparticles as seeds, which catalyzed H2O2 reduction of the residual Au(III), thus accelerating the formation of compact 3D gold nanoflowers. The key synthesis strategy was to use protocatechuic aldehyde as a structure-induced agent to influence the growth of gold nanoflowers. The pH value of growth solution could tune the size and/or morphology of gold nanoflowers through its influence on the adhesion force of protocatechuic aldehyde on gold surfaces and the species type of Au(III) complexes. When the pH value of growth solution was above 7.26 (the pKa of protocatechuic aldehyde), the flower-like of gold nanostructural architectures with different sizes could be fabricated. The obtained gold nanoflowers had a large dimension of 198 and 157 nm at the pH of 7.6 and 8, respectively. Size control of gold nanoflowers can be accomplished in the growth solutions of pH 9.4-12.0 with a similar diameter around 60 nm. The as-synthesized gold nanoflowers exhibited good stability and have the prospects for surface-enhanced Raman scattering enhancement.

Rh and Au deposited on ultrathin TiO~1.2 film formed on Rh(111) facets and the effects of CO exposure

Abstract This STM study deals with the structure and reactivity of Rh and Au deposited on a “pinwheel” TiO~ 1.2 ultrathin film (w-TiO-UTO) formed on Rh nanoparticles supported on TiO2(110). The deposition of a monolayer (ML) Au at 500 K disturbed the order of the w-TiO-UTO layer and led to the formation of 3D adparticles. The deposition of Rh (~ 1 ML) at 500 K and annealing up to 900 K led exclusively to the formation of 2D adparticles. It was found that 3D Au nanoparticles are gradually sintering in the range of 500–800 K. Upon a further raise of the temperature, a 3D→2D transformation takes place. The main difference is that on the top facet of the 2D Rh particles a w-TiO-UTO film forms, while the top facets of the 2D Au particles exhibit a clean gold metal structure. CO exposure of max. 10 min at 10 Pa causes no remarkable change of the encapsulated Rh particles, however, the 2D gold nanoparticles change significantly. The disintegration of Au particles and the spillover of Au atoms to the UTO surface accelerate at a CO pressure above 10− 1 Pa. This morphological process is reversible as an effect of annealing in UHV.

Gold Nanoparticle Arrays Spectroscopy: Observation of Electrostatic and Radiative Dipole Interactions

In this paper, localized surface plasmon resonance (LSPR) of periodic two-dimensional (2D) gold nanoparticles arrays is investigated using far field polarization spectroscopy. Square and rectangular arrays of 60 nm gold nanoparticles with different interparticle spacings are fabricated with electron beam lithography (EBL). The experimental extinction cross section spectra are revealed the existence of two plasmon modes depending to the polarization direction of the incident radiation on the sample. The extinction spectra are calculated using coupled dipole approximation (CDA). Good qualitative and quantitative agreement is obtained between calculations and experimental results. Moreover, it is found that the interparticle spacing on the array was the key parameter to study the plasmon interaction between the nanoparticles and to determine the amplitude, spectral position and width of LSPR band.