Au Nanoplates Research Articles

A facile electrochemical sensor based on reduced graphene oxide and Au nanoplates modified glassy carbon electrode for simultaneous detection of ascorbic acid, dopamine and uric acid

A facile Au nanoplates and reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was fabricated via a simple electrochemical method, denoted as Au/RGO/GCE. The Au/RGO/GCE electrode was used for the simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The modified electrodes fabricated by different methods presented different morphologies and performances for determination of AA, DA, and UA. Three well-defined voltammetric peaks along with remarkable increasing electrooxidation currents were obtained on the Au/RGO/GCE with needle-like Au nanoplates in differential pulse voltammetry (DPV) measurements. It was found that there are linear relationships between the peak currents and the concentrations in the range of 2.4×10−4 to 1.5×10−3M (AA), 6.8×10−6 to 4.1×10−5M (DA), and 8.8×10−6 to 5.3×10−5M (UA), and the limits of simultaneous determination (based on S/N = 3) are 5.1×10−5M, 1.4×10−6M, and 1.8×10−6M for AA, DA and UA, respectively. Additionally, the Au/RGO/GCE electrode presented well anti-interference ability, stability and reproducibility.

A novel high efficiency composite catalyst: single crystal triangular Au nanoplates supported by functional reduced graphene oxide.

To improve the utilization efficiency of Au catalyst, triangular Au nanoplates on functional reduced graphene oxide were prepared by a facile method. The products with ultra-low trace amounts of Au afforded high catalytic efficiency for the reduction of 4-nitro phenol. The morphology of the products was controlled by tuning the addition of HAuCl4.

Enhancing nanoparticle electrodynamics with gold nanoplate mirrors.

Mirrors and optical cavities can modify and enhance matter-radiation interactions. Here we report that chemically synthesized Au nanoplates can serve as micrometer-size mirrors that enhance electrodynamic interactions. Because of their plasmonic properties, the Au nanoplates enhance the brightness of scattered light from Ag nanoparticles near the nanoplate surface in dark-field microscopy. More importantly, enhanced optical trapping and optical binding of Ag nanoparticles are demonstrated in interferometric optical traps created from a single laser beam and its reflection from individual Au nanoplates. The enhancement of the interparticle force constant is ≈20-fold more than expected from the increased intensity due to standing wave interference. We show that the additional stability for optical binding arises from the restricted axial thermal motion of the nanoparticles that couples to and reduces the fluctuations in the lateral plane. This new mechanism greatly advances the photonic synthesis of ultrastable nanoparticle arrays and investigation of their properties.

Site-specific growth of a Pt shell on Au nanoplates: tailoring their surface plasmonic behavior.

In this report, we tune the surface plasmonic behavior of Au nanoplates depending on the morphology of the Pt shell in which Pt is considered as a less optically inactive element. We describe the synthesis of flat Au nanoplates coated with Pt via rim-preferential or uniform growth methods. Depending on the site-selective growth of Pt on core Au nanoplates, the aspect ratio of the resulting Au@Pt nanoplates was tunable and their corresponding surface plasmon resonance (SPR) bands were controlled accordingly. Although Pt is regarded as an optically weak component in visible and near infrared spectral windows, a Pt coating affects the SPR behavior of core Au nanoplates due to effective surface plasmon (SP) coupling between the Au core and the deposited Pt shell. We systematically investigated the optical properties of uniformly grown (Au@Pt(uni)) and rim-preferentially grown (Au@Pt(rim)) Au@Pt nanoplates by observing their SPR band shifts compared to SPR of Au nanoplates. Due to the structural rigidity conferred by the Pt coating, the Au@Pt nanoplates can be easily transferred to the investigated solvents.

High-yield synthesis of triangular gold nanoplates with improved shape uniformity, tunable edge length and thickness.

We report the synthesis of uniform triangular gold nanoplates by a modified seeded growth method. The concentration of cetyltrimethylammonium bromide (CTAB) in the growth solution and the time interval between multiple steps of growth were important factors which determined the formation of uniform triangular Au nanoplates. In addition, by further isotropic overgrowth, the thickness of triangular Au nanoplates can be finely tuned within a wide range of 10-80 nm, which at present remains a challenge using conventional seeded growth.

Facile preparation of SERS-active nanostructured Au spheres by simple reduction of [formula omitted] ions with EDOT

Uniform submicron-scale Au spheres with an average dimension of 574nm were facilely prepared from the redox reaction between HAuCl4 and 3,4-ethylenedioxythiophene (EDOT) in aqueous solution under ambient conditions. HAuCl4 precursor readily polymerized to poly(3,4-ethylenedioxythiophene) (PEDOT) and metallic Au spheres simultaneously formed within a short period of time. The Au spheres are consisted of two slightly different types of spherical particles based on their surface textures. Major raspberry-like Au spheres are formed through the assembly of very tiny Au nanoparticles, while minor rosette-like Au spheres are formed through the dense packing of Au nanoplates. Both Au spheres are pure metallic face-centered cubic Au based on X-ray photoelectron spectroscopy and powder X-ray diffraction. The resultant Au spheres are adequate for application to surface-enhanced Raman scattering (SERS) due to their rough surfaces and nanogaps on the surfaces. Both methylene blue and crystal violet molecules were detectable at concentrations as low as 10−7M.

Au nanoplates as robust, recyclable SERS substrates for ultrasensitive chemical sensing

With the structural advantages of being sharp and straight, Au nanoplates may work as a promising surface-enhanced Raman scattering (SERS) platform for detection of Raman-sensitive analytes. However, the utilization of Au nanoplates as realistic SERS substrates is still not widely investigated, especially in the practical detection of environmentally persistent pollutants. This work delivers the first successful demonstration of using Au nanoplate platform in practical SERS sensing toward a typical polycyclic aromatic hydrocarbons pollutant of pyrene. The samples were prepared using an environmentally benign seed-mediated growth approach without the post-purification treatment. It was found that Au nanoplates exhibited significantly enhanced SERS activities (enhancement factor=7.30×107) and achieved an extremely low detection limit (5×10−10M) toward pyrene molecules. Furthermore, the SERS activity of Au nanoplates can be fully recovered after repeatedly used and recycled in pyrene detection. These results manifest that the present Au nanoplates can serve as robust, recyclable SERS substrates that allow rapid detection of trace levels of analytes with a high degree of sensitivity and stability. The findings from this work may facilitate the use of Au nanoplate SERS substrates in more realistic applications such as biomolecule sensing and environmental monitoring.

2-Thiopheneacetic Acid Directed Synthesis of Au Nanorosette as an SERS-Active Substrate

Rosette-like nanoscale Au materials were simply prepared through one-pot reduction of the AuCl₄⁻ precursor by 2-thiopheneacetic acid (2-TAA) without extra surface capping ligands at room temperature. 2-TAA underwent polymerization into polythiophene derivatives while the AuCl₄⁻ precursor was simultaneously reduced into various Au nanostructures. In situ generated polythiophene derivatives played a significant role of surface passivation in guiding the shape of Au nanostructures. The morphology of Au nanostructures was strongly dependent on the molar ratio of 2-TAA to AuCl₄⁻. At lower [2-TAA]/[AuCl₄⁻] ratios, uniform rosette-like Au microparticles consisting of 30-nm-thick Au nanoplates were observed. The Au nanoplates had either triangular prismatic or hexagonal geometry with many defects. Uniform Au nanorosettes could be easily deposited on the Si substrate by drop-casting and were subsequently used as highly active SERS substrates for the detection of methylene blue and crystal violet by Raman spectroscopy. Upon increasing the ratio of [2-TAA]/[AuCl₄⁻], Au nanoparticles or nanorods heavily surrounded with polythiophene polymers were obtained.

Single-Molecule Catalysis Mapping Quantifies Site-Specific Activity and Uncovers Radial Activity Gradient on Single 2D Nanocrystals

Shape-controlled metal nanocrystals are a new generation of nanoscale catalysts. Depending on their shapes, these nanocrystals exhibit various surface facets, and the assignments of their surface facets have routinely been used to rationalize or predict their catalytic activity in a variety of chemical transformations. Recently we discovered that for 1-dimensional (1D) nanocrystals (Au nanorods), the catalytic activity is not constant along the same side facets of single nanorods but rather differs significantly and further shows a gradient along its length, which we attributed to an underlying gradient of surface defect density resulting from their linear decay in growth rate during synthesis (Nat. Nanotechnol.2012, 7, 237-241). Here we report that this behavior also extends to 2D nanocrystals, even for a different catalytic reaction. By using super-resolution fluorescence microscopy to map out the locations of catalytic events within individual triangular and hexagonal Au nanoplates in correlation with scanning electron microscopy, we find that the catalytic activity within the flat {111} surface facet of a Au nanoplate exhibits a 2D radial gradient from the center toward the edges. We propose that this activity gradient results from a growth-dependent surface defect distribution. We also quantify the site-specific activity at different regions within a nanoplate: The corner regions have the highest activity, followed by the edge regions and then the flat surface facets. These discoveries highlight the spatial complexity of catalytic activity at the nanoscale as well as the interplay amid nanocrystal growth, morphology, and surface defects in determining nanocatalyst properties.

Optical and Dynamical Properties of Chemically Synthesized Gold Nanoplates

Single crystal, micrometer-sized nanoplates were formed by reducing Au(III) in the presence of surfactants using a modified polyol protocol. The shapes of the plates range from triangular to hexagonal. The nanoplates have {111} surfaces with an average edge length of 5 ± 2 μm and an average width of 107 ± 30 nm. Scanning electron microscopy (SEM) images reveal that the plates grow through a re-entrant groove created by twinning. The optical properties of the plates were studied by scattered light and transient absorption experiments. The scattered light measurements show that propagating surface plasmon polariton (SPP) modes of the Au nanoplates can be excited when a laser beam is focused at the edge of the nanoplate. We also demonstrate that the direction of propagation of the SPP modes can be controlled through the polarization of the laser beam. The transient absorption traces for single suspended nanoplates show oscillations, which are assigned to thickness vibrations of the plates. The quality factors for the oscillations are smaller than those recently measured for suspended gold nanowires, indicating possible contributions to the vibrational damping from surface bound molecules or from the crystal structure.

Facile synthesis of single crystalline gold nanoplates and SERS investigations of 4-aminothiophenol

Single crystalline gold nanoplates with micrometer-scale sizes that are tens of nanometers in thickness were synthesized by reducing HAuCl4 with the disodium salt of ethylenediaminetetraacetic acid (Na2EDTA) in the presence of hexadecyltrimethylammonium bromide (CTAB) in aqueous solution. The results indicated that CTAB plays an important role in the formation of single crystalline gold nanoplates. The application of the as-prepared nanoplates in surface-enhanced Raman spectroscopy (SERS) was investigated by using 4-aminothiophenol (PATP) as probe molecules. As a result of the sharp corners and edges in their shape, the resultant Au nanoplates exhibit excellent Raman enhancement ability. It was found that PATP can be oxidatively transformed into 4,4′-dimercaptoazobenzene on the surface of Au nanoplates during the SERS measurement.

Synthesis of Gold Nanoplates with Bioreducing Agent Using Syringe Pumps: A Kinetic Control

Anisotropic Au nanoplates are particularly important owing to their unusual properties. Herein, we describe a plant-mediated bioreduction method to increase the yield of Au nanoplates and shorten the reaction time through a kinetically manipulated procedure. More specifically, the reduction rate was controlled by modulating experimental factors such as the addition mode and rate of the feed solutions, the temperature, and the pH based on a syringe-pumps apparatus. The dimensions of the obtained Au nanoplates were measured using TEM and AFM. The single-crystalline structure was demonstrated by HRTEM, SAED, and XRD. The results of XPS, FTIR, and TG analyses indicated strong affinity of the biomolecules binding to the Au nanoplate facets. In particular, the nanoplate films exhibited strong surface plasmon absorbance in the near-infrared range of 700–3000 nm, vital for optical applications. Furthermore, we propose a mechanism for this formation following the time-resolved studies.

Plasmonic enhancements of photoluminescence in hybrid Si nanostructures with Au fabricated by fully top-down lithography.

The authors study plasmonic enhancements of photoluminescence (PL) in Si nanodisk (ND) arrays hybridized with nanostructures such as nanoplates of Au, where these hybrid nanostructures are fabricated by fully top-down lithography: neutral-beam etching using bio-nano-templates and high-resolution electron-beam lithography. The separation distance between the Si ND and Au nanostructure surfaces is precisely controlled by inserting a thin SiO2 layer with a thickness of 3 nm. We observe that PL intensities in the Si NDs are enhanced by factors up to 5 depending on the wavelength by integrating with the Au nanoplates. These enhancements also depend on the size and shape of the Au nanoplates.

<I>γ</I>-Radiation Synthesis of Nano/Micrometer-Scale Single-Crystalline Large Gold Plates

An original solution phase approach was developed for the synthesis of single-crystal Au nanoprims with anisotropic structure of triangular, hexagonal and truncated triangular, nanometre or micrometer scale, and nanometer thickness. It has been confirmed that the Fe3O4 magnetite nanoparticles and (3-aminopropyl) triethoxysilane (APTES) coated on the magnetite nanoparticles play important roles in the formation of Au nanoplates. Significantly, such Au nanoplates exhibit remarkable optical properties, both the dipole plasmon resonance and the quadrupole plasmon resonance were observed. And the selected area electron diffraction (SAED) pattern shows the nanoplates obtained were single crystals with (111) plans as two basal surfaces. The growth of gold nanoplates in the solution with time had been monitored by microscopic and spectroscopic techniques to allow the detection of several key intermediates in the growth process. To our knowledge, this is the first report on the production of large planar gold nanostructures with gamma irradiation in combination of another nanocomposite materials (APTES-Fe3O4).

Structural evolution of Ag–Au nanoplates by pH controlled galvanic displacement

In this study, we performed a systematic study of the replacement reaction between silver nanoplates and an aqueous HAuCl4 solution. The aqueous HAuCl4 solution was adjusted to various pH values before the reaction. Under the different pH conditions, the hydrolyzed Au complexes existing in the solution have different concentrations. As a result, the total standard potential of the solution decreased with increasing pH. Thus, the pH was used to investigate the morphological, structural, compositional, and spectral changes of the reaction on the nanoscale. The alloy and dealloying processes were monitored and different structures were obtained. This work has enabled us to prepare metal nanostructures with controllable shapes at room temperature and their optical properties could be readily tuned by adjusting the pH.

Shape-controlled synthesis of Pt nanoframes

Plate-like Pt nanoframes were synthesized using Au nanoplates as a template, followed by formation of a Ag layer coating on the Au template, and selective chemical etching of Au and Ag leaving the Pt structure intact. Circular, triangular, and hexagonal Au nanoplates successfully served as templates for fabrication of various Pt nanoframe shapes, which resembled the original Au nanoplate shape. A thin Ag layer was found to play a critical role as an electron-transfer mediator in the galvanic replacement reaction between the thin Ag layer on Au nanoplates and Pt precursors. During the replacement reaction, the Pt layer grew faster at the {112} edges than at the {111} terraces of Au nanoplates. The thicker periphery of the nanoplates survived the chemical etching step, while the thinner center was etched, leading to formation of Pt nanoframes in high yield and good homogeneity.

Direct deposition of gold nanoplates and porous platinum on substrates through solvent-free chemical reduction of metal precursors with ethylene glycol vapor

Deposition of nanostructured metals on substrates is important for the fundamental study and practical application, such as in optics and catalysis. In this paper, we report the deposition of gold (Au) nanoplates and porous platinum (Pt) structures on substrates through solvent-free chemical reductions of chloroauric acid (HAuCl(4)) and chloroplatinic acid (H(2)PtCl(6)) with ethylene glycol (EG) vapor at temperatures below 200 °C. The process includes two steps. The first step is the formation of a thin layer of a metal precursor on substrates by coating solution of a metal precursor. The thin metal precursor layer is subsequently dried by annealing. The second step is the chemical reduction of the metal precursor with EG vapor at 160 or 180 °C in the absence of solvent. Both the Au and Pt nanostructures deposited by this method have good adhesion to substrates, but they have different morphologies. The Au nanostructures appear as separate two-dimensional islands on the substrates, and up to 70% of them can be triangular nanoplates with the (111) crystal plane as the basal plane. In contrast, the reduction of H(2)PtCl(6) gives rise to a 3-dimensional porous Pt structure on substrates. The different morphologies of nanostructured Au and Pt are tentatively related to the different surface energies of Au and Pt.

Template-free synthesis of large anisotropic gold nanostructures on reduced graphene oxide

The morphologies/dimensions of Au nanostructures can be tailored by merely controlling the reduction degree of graphene oxide surface. Au nanoparticles, long Au nanowires, and semicircular-shaped Au nanoplates are in situ synthesized on slightly, moderately, and highly reduced graphene oxide films respectively, without the need of any templating agent.

Au nanoplate/polypyrrole nanofiber composite film: preparation, characterization and application as SERS substrate

Without any other additives or additional energy, Au nanoplates have been successfully prepared and integrated simultaneously with the dedoped polypyrrole nanofiber film via the in situ reduction of AuCl4– on the film surface. The morphology and structure of the as‐prepared composite film are characterized, and its application for surface‐enhanced Raman scattering is also investigated. It has been found that the morphology of as‐prepared Au nanoplates is dependent on the reaction duration, while the density is dependent on the concentration of AuCl4– ions in the reaction process. It is suggested that polypyrrole plays dual reducing and structure‐directing roles during the formation of Au nanoplates. Surface‐enhanced Raman scattering study shows that the Au nanoplates give an intensive and enhanced Raman scattering when 4‐aminothiophenol is used as a probing molecule. The employed approach may shed some light on simultaneously fabricating and immobilizing other noble metal micro/nanostructures with unique morphology. Copyright © 2011 John Wiley & Sons, Ltd.

A novel strategy to synthesize Au nanoplates and their application for enzymeless H 2O 2 detection

The present communication reports a novel and simple strategy to synthesize Au nanoplates (AuPs) by heating an aqueous solution of HAuCl 4 in the presence of poly [(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11). Direct placing of the resultant dispersion on a glassy carbon electrode (GCE) surface gives a very stable AuPs-containing film exhibiting remarkable catalytic performance toward both the oxidation and reduction of H 2O 2. This enzymeless H 2O 2 sensor shows a fast amperometric response time of less than 3 s and the corresponding linear range and detection limit are estimated to be from 0.1 mM to 50 mM ( r = 0.999) and 4 μM at a signal-to-noise ratio of 3, respectively.