Nanometer-sized Gold Research Articles

Metal nanoparticle-based electrochemical stripping potentiometric detection of DNA hybridization.

A new nanoparticle-based electrical detection of DNA hybridization, based on electrochemical stripping detection of the colloidal gold tag, is described. In this protocol, the hybridization of a target oligonucleotide to magnetic bead-linked oligonucleotide probes is followed by binding of the streptavidin-coated metal nanoparticles to the captured DNA, dissolution of the nanometer-sized gold tag, and potentiometric stripping measurements of the dissolved metal tag at single-use thick-film carbon electrodes. An advanced magnetic processing technique is used to isolate the DNA duplex and to provide low-volume mixing. The influence of relevant experimental variables, including the amounts of the gold nanoparticles and the magnetic beads, the duration of the hybridization and gold dissolution steps, and the parameters of the potentiometric stripping operation upon the hybridization signal, is examined and optimized. Transmission electron microscopy micrographs indicate that the hybridization event leads to the bridging of the gold nanoparticles to the magnetic beads. Further signal amplification, and lowering of the detection limits to the nanomolar and picomolar domains, are achieved by precipitating gold or silver, respectively, onto the colloidal gold label. The new electrochemical stripping metallogenomagnetic protocol couples the inherent signal amplification of stripping metal analysis with discrimination against nonhybridized DNA, the use of microliter sample volumes, and disposable transducers and, hence, offers great promise for decentralized genetic testing.

Fabrication of gold nanowires on insulating substrates by field-induced mass transport

A method for the fabrication of nanometer size gold wires on insulating surfaces is presented. An oscillating gold-coated atomic force microscope tip is brought into close proximity of a silicon dioxide surface. The application of a negative sample voltage produces the transport of gold atoms from the tip to the surface. The voltage is applied when there is a tip–surface separation of ∼3 nm. The finite tip–surface separation enhances the tip lifetime. It also allows the application of sequences of multiple voltage pulses. Those sequences allow the fabrication of continuous nanowires. The atomic force microscope gold deposition is performed at room temperature and in ambient conditions which makes the method fully compatible with standard lithographic techniques. Electron transport measurements of the wires show a clear metallic behavior. Electrical resistivities of ∼3×10−7 Ω m and current densities of up to 5×1011 A m−2 are reported.

Encapsulation, Permeability, and Cellular Uptake Characteristics of Hollow Nanometer-Sized Conductive Polymer Capsules

The use of nanometer-sized gold particles as templates for the synthesis of hollow poly(pyrrole), poly(N-methylpyrrole), and poly(3-methylthiophene) is described in this paper. Diffusion coefficients of small molecules through the capsule shell were found to vary by almost 3 orders of magnitude depending on the polymer, polymer oxidation state, and counteranion incorporated during polymer synthesis. A small molecule (anthraquinone) and an enzyme (horseradish peroxidase) were trapped inside hollow capsules by attaching them to the template particle prior to polymerization and particle etching. A thin poly(pyrrole) shell protected the enzyme 2 times longer in neat toluene compared to unencapsulated enzyme. Finally, the potential for using conductive polymer nanoparticles for intracellular delivery or diagnostics was examined by administering partice suspensions to 3T3 murine fibroblasts. Particles ranging in size from 25 to 100 nm were engulfed by fibroblasts without compromising cell viability.

Alloy phase formation in nanometer-sized particles

Alloy phase formation in nanometer-sized particles has been studied by transmission electron microscopy using particles in the Au–Sn system. When tin atoms are vapor-deposited onto nanometer-sized gold particles, rapid dissolution of tin atoms into gold particles takes place, and as a result, particles of an Au-rich solid solution, of a topologically disordered amorphous-like alloy and of the AuSn compound are formed, depending upon the concentration of tin in a composition range from 0 to 59 at.% Sn. A remarkable enhancement of solubility has been observed in the Au-rich solid solution and the AuSn compound. There is a possibility that the topologically disordered amorphous-like phase, which appears in the middle of a two-phase region (i.e. Au 5Sn–AuSn region) of the phase diagram for the bulk alloy, is not a non-equilibrium phase.

Time-resolved high-resolution transmission electron microscopy and high-angle annular dark field scanning transmission electron microscopy of metal-mediated crystallization of amorphous germanium films

Metal mediated crystallization of amorphous germanium (a-Ge) films was studied through ‘in-situ’ heating by time-resolved high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), mainly on a-Ge films with nanometer-sized gold clusters on the surfaces. It was revealed from the dynamic HRTEM observations that the interface between crystalline gold and a-Ge was a bit melted due to alloying even at 70°C and liquid-like gold-rich alloys migrate on the a-Ge films to initiate the crystallization, which was confirmed also through the static observations with HAADF-STEM.

Particle Crystals of Surface Modified Gold Nanoparticles Grown from Water

Abstract Surface modified nanometer-sized gold particles with mercaptosuccinic acid (MSA) are crystallized in the size range of a few micrometer. Two dimensional superlattice was also generated in the same system. The transmission electron microscope images of these superstructures and the reflectance spectrum are reported in comparison with that of bulk sample.

Thermal diffusion and soret feedback of gold-doped polyorganosiloxane nanospheres in toluene

We have investigated diffusion and thermal diffusion properties of light-absorbing colloidal polyorganosiloxane microgels containing tiny nanometer-sized gold clusters dispersed in toluene. Transient holographic gratings allow for very subtle perturbations in the linear regime where Soret feedback is negligible. Gold-doped colloids of different size and crosslink ratios show different Soret coefficients but identical thermal diffusion coefficients D(T). Undoped colloids tend to aggregate, but a consistent interpretation is obtained if an identical D(T) is assumed for the doped, the undoped, and the aggregated particles. Previously reported Soret feedback measurements on similar systems incidentally yielded comparable Soret coefficients. We show, however, that they suffer from strong convective perturbations.

Growth and characterization of Au clusters on alkanethiol self-assembled monolayers

We have prepared nanometer-sized gold clusters on alkanethiol [CH3(CH2)n−1SH, abbreviated as Cn] self-assembled monolayers (SAMs) on Au(111) substrates by thermal evaporation. Typically, the Au clusters are one atomic layer thick and plate-like, with a diameter of ∼2–10 nm. While most of the Au clusters are found at the SAM/Au(111) interface, a fraction of the clusters reside on top of the SAMs as evidenced by the existence of the Coulomb blockade and Coulomb staircase in the scanning tunneling spectroscopy. Using scanning tunneling microscopy under ambient conditions, we also investigated the stability of the gold clusters at the SAM/Au(111) interface. For a given nominal coverage of Au, the gold clusters on C7 are larger and diffuse faster than those on C10 and C18.

Deposition mechanism of gold by thermal evaporation: approach by charged cluster model

The charged cluster model states that chemical vapor deposition (CVD) begins with gas-phase nucleation of charged clusters followed by cluster deposition on a substrate surface to form a thin film. Gold deposition by thermal evaporation was studied in a two-chambered CVD system in order to determine if this mechanism applies to the present case. The presence of nanometer-sized gold clusters was confirmed by transmission electron microscopy (TEM). The charge on the primary clusters was found to be positive. Smaller clusters were found to be amorphous and combined with clusters already deposited on a substrate surface to form larger amorphous clusters on the surface. Larger clusters were also observed by TEM to form after 120 and 300 s. These clusters exhibited a lattice structure and may have grown by attachment of small clusters in the gas phase.

Spontaneous alloying of tin atoms into nanometer-sized gold clusters and phase stability in the resultant alloy clusters

Alloying behavior and phase stability has been studied in situ by transmission electron microscopy using clusters in the Au-Sn system. When tin atoms are vapor-deposited onto nm-sized gold clusters, rapid dissolution of tin atoms into gold clusters takes place and as a result Au-rich solid solution, amorphous-like Au-Sn alloy and AuSn compound clusters are formed depending upon the concentration of tin. The remarkable enhancement of solubility has been observed in Au-rich solid solution and AuSn compound. It becomes more difficult to form two phases in the interior of individual clusters even if the composition of alloy clusters falls in the two-phase region in the phase diagram for the bulk alloy and as a result amorphous-like phase is stabilized in nm-sized Au-Sn alloy clusters.

Genesis of Carlin-type gold deposits in southwestern Guizhou Province, China

A solution containing nanometer-sized pure gold particles was prepared with the hydrolysisreduction method. As observed under the electron microscope, the gold particles were as large as 2–20 nm in size. Different kinds of mineral and rock were put into the solution and the experimental result showed that the nanometer-sized gold particles are obviously adsorbed on sulfide minerals, native copper and carbonaceous rocks. This experimental result is consistent with the actual geological observation. On this basis a better explanation is presented of the genesis of the Carlin-type gold deposits.

Alloying Reaction between Nanometer-Sized Indium and Gold Particles at Reduced Temperatures

Alloying Reaction between Nanometer-Sized Indium and Gold Particles at Reduced Temperatures

Alloying Reaction between Nanometer-Sized Indium and Gold Particles at Reduced Temperatures

Alloying Reaction between Nanometer-Sized Indium and Gold Particles at Reduced Temperatures

Electrochemical Charge Injection into Immobilized Nanosized Gold Particle Ensembles: Potential Modulated Transmission and Reflectance Spectroscopy

Self-assembled multilayer thin films of nanometer-sized gold particles linked with organic dithiols have been prepared on glass, indium tin oxide, and gold substrates. The gold particles within these structures retain their integrity and no sintering occurs as demonstrated by their optical absorbance, ellipsometry, and potential modulated transmission and reflectance spectroscopy. The optical response to electrochemical charge injection into the outermost layer of gold particles is completely different from that of bulk gold electrodes, and it is concluded that the particles have to be regarded as discrete, immobilized quantum-dots.

Coulomb blockade phenomena in ultrathin Langmuir-Blodgett sandwich junctions

Electrical junctions were fabricated in sandwich configuration from Langmuir-Blodgett (LB) films of two types of material, -conjugated, peripherally substituted ring systems or a -bonded polymer. The sandwich junctions consisted of four to ten monolayers between two micro-structured gold electrodes, corresponding to a nominal film thickness between about 8 and 20 nm. At liquid helium temperature, the current (I)/voltage (V) characteristics generally exhibited smooth exponential behaviour or irregular steps. However, for a small fraction of the LB sandwiches comprising a -conjugated or -bonded compound, regular staircases were observed. It was possible to fit such characteristics with curves calculated on the basis of a Coulomb blockade model. These results are accounted for by the presence of nanometre-sized gold particles formed upon evaporation of the top electrode. Single electron tunnelling is assumed to proceed through double tunnel barrier junctions consisting of a gold island asymmetrically located between the top and bottom electrode.

Arenethiolate Monolayer-Protected Gold Clusters

Nanometer-sized gold clusters stabilized by monolayers of arenethiolates prepared using the Brust reaction are somewhat larger (by TEM) and less thermally stable (by TGA) than those prepared under similar conditions and stabilized by alkanethiolates. Like the latter, the mean core size decreases for synthetic conditions based on larger thiol/Au ratios. The differential pulse voltammetry of the arenethiolates was especially interesting by displaying electrochemical ensemble Coulomb staircase features analogous to those recently reported, even in unfractionated cluster preparations, consistent with a smaller dispersity of core sizes than usual for alkanethiolate-protected clusters. The spacings between quantized capacitance charging features on the potential axis decrease with decreasing methylene linker chain length. TEM studies show chain/ring self-organization features. The UV−vis spectral surface plasmon bands of the arenethiolate clusters are virtually independent of the specific aryl ligands for small cluster sizes; for others a collective band feature might be due to the formation of small aggregates of MPCs.

Atomic Process of Point Contact in Gold Studied by Time-Resolved High-Resolution Transmission Electron Microscopy

Contact and subsequent retraction between nanometer-sized gold tips were controlled at an atomic scale using a piezoelectric device at room temperature inside a high-resolution transmission electron microscope. The atomic process of the point contact was observed in situ at a spatial resolution of 0.2 nm and at a time resolution of $\frac{1}{60}\mathrm{s}$. It was shown that an atomistic pillarlike elongated neck is formed by lattice slip and structural relaxation during retraction.

Accelerating the Kinetics of Thiol Self-Assembly on GoldA Spatial Confinement Effect

The adsorption of alkanethiols onto gold surfaces to form self-assembled monolayers (SAMs) occurs more than 10 times faster in a spatially confined environment than on unconfined bare substrates, and the adsorbed layers exhibit higher coverage and two-dimensional crystallinity. The spatially constrained reaction environment is prepared with use of an atomic force microscope tip to displace thiols within a previously formed SAM. During the displacement, the thiol molecules present in the solution above the SAM rapidly assemble onto the exposed nanometer-size gold area that is confined by the scanning tip and surrounding SAM. The accelerated rate is attributed to a change in the pathway for the self-assembly process as the spatial confinement makes it geometrically more probable and energetically more favorable for the initially adsorbed thiols to adopt a standing-up configuration directly in this microenvironment. In contrast, thiols that self-assemble onto gold surfaces in an unconstrained environment ini...

Amperometric Biosensor for Glucose Based on a Nanometer-Sized Microband Gold Electrode Coimmobilized with Glucose Oxidase and Poly(o-phenylenediamide)

A nanometer-sized (88 mm) microband gold electrode for glucose detection is described. These noble metal ultramicrosensors are prepared by electrochemical copolymerization of o-phenylenediamide (PDA) and glucose oxidase at the nanometer-sized electrodes. Electropolymerization conditions of PDA at the microband surface are optimized. The current can rapidly (3s) reach a steady value upon the potential step from 0 to +0.6 V without stirring the solution. The permselectivity characteristics of polymer can eliminate the interference of ascorbic acid. The amperometric response to glucose shows a linear relation in the range of 0.5 mM to about 10 mM with the correlation coefficient of 0.9993. With further increasing of glucose concentration an obvious Michaelis-Menten's response can be observed. The maximum steady current density is ca. 4.4 ± 0.2 mA/cm2 and the apparent Michaelis-Menten constant is 21.1 ± 0.2 mM.

Amperometric Biosensor for Glucose Based on a Nanometer-Sized Microband Gold Electrode Coimmobilized with Glucose Oxidase and Poly(o-phenylenediamide)

Amperometric Biosensor for Glucose Based on a Nanometer-Sized Microband Gold Electrode Coimmobilized with Glucose Oxidase and Poly(o-phenylenediamide)