Single Au Nanoparticles Research Articles

Experimental and Theoretical Analysis of Photofragmentation of Au Nanoparticles by Picosecond Laser Radiation

This paper presents a novel model aimed at describing the basic phenomena that cause the fragmentation of a single Au nanoparticle (AuNP) by interaction with the second and the third harmonics of a...

Ultrasensitive chemiluminescence quantification of single-nucleotide polymorphisms by using monobase-modified Au and CuS nanoparticles

An ultrasensitive chemiluminescence method based on the Au nanoparticles amplification for the quantitative detection of single-nucleotide polymorphisms (SNPs) in genomic DNA was accomplished by the DNA polymerase I (Klenow fragment)-induced coupling of the nucleotide-modified nanoparticle probe to the mutant sites of duplex DNA under the Watson–Crick base-pairing rule. The concentration of the one-base mutant DNA was determined by chemiluminescence (CL) detection of the cupric ions dissolved from the CuS nanoparticles (NPs) modified on the Au NPs. The incorporation of Au NPs in this method significantly enhanced the sensitivity because a single Au NP can be loaded with 77 CuS NPs through the link-age of an amidization reaction between mercaptoacetic acid on the surface of Au NPs and aminoethanethiol on the surface of CuS NPs. A preconcentration process of cupric ions performed by anodic stripping voltammetric (ASV) technology further increased the sensitivity of the design for about 10-fold. As a result of these two combined effects, this method could detect as low as 19 aM SNPs and the linear range for SNPs was from 8.0 × 10 −17 to 1.0 × 10 −14 M.

Nanoscale Architecture Dictates Detection Profile of Surface-Confined DNA by MALDI-TOF MS

The design and fabrication of various nanoscale architectures for the effective MALDI-TOF MS analysis of surface-confined DNA are reported. The nanoscale architectures are derived from layer-by-layer assemblies of negatively charged nanoparticles and positively charged polymers. An important finding is that porous structures comprising bottom SiO(2) nanoparticle layers and top Au nanoparticle layers enable the observation of both covalently bound (with Au-S bond) and hybridized oligonucleotides. The achievement of this unprecedented detection capability is attributed to the unique combination of a nanoporous dielectric film and discrete noble metal nanoparticles. The conclusion is supported by control experiments performed on a variety of single and multilayered Au nanoparticle structures, where only the hybridized oligonucleotides in a two- or three-strand system could be detected.

Controlled Assembly of Gold Nanoparticles and Graphene Oxide Sheets on Dip Pen Nanolithography-Generated Templates

The ability to organize nanomaterials, e.g., Au nanoparticles (NPs) and graphene oxide (GO) sheets, into ordered structures with high accuracy and resolution on a substrate is crucially important for fundamental studies and applications. In this letter, we developed a simple and efficient method to generate positively charged 11-amino-1-undecanethiol (AUT) templates on Au substrates, which were successfully used for controlled assembly of negatively charged Au NPs or GO sheets from aqueous solution. The templates were obtained by passivation of the exposed Au area with AUT after 16-mercaptohexadecanoic acid (MHA) patterns were generated by dip-pen nanolithography (DPN) on Au. The electrostatic interaction ensures that the Au NPs and GO sheets only adsorb on the designed AUT areas. Importantly, by using this method, the number of Au NPs adsorbed on patterned areas can be controlled, and a single Au NP array was successfully achieved.

The temperature-dependent physical and electrical characteristics of a polymer/RAFT-polymerstabilized nanoparticle system for organic nonvolatile memory

We have fabricated and investigated organic memory diodes, comprising a single polymerlayer and Au nanoparticles stabilized by the same polymer material utilizing areversible addition–fragmentation transfer technique to suppress phase separation.The organic memory diodes exhibit well reproducible and prominent currentbistability and good charge retention characteristics free from phase separation issues.Nondestructive spectroscopic ellipsometry is used to characterize the physical properties ofthe polymer/nanoparticle composites, such as the polymer’s effective dielectricfunction/layer thickness and the Au nanoparticle’s effective volume fraction, which areimportant parameters for gaining insightful information on charge transport in thissystem. Temperature-dependent analysis of the read/write current behaviorssuggests that charge transport in such a polymer/Au nanoparticle composite isdominated by carrier hopping via shallow-level traps at the high field regime.

Random walk of single gold nanoparticles in zebrafish embryos leading to stochastic toxic effects on embryonic developments

We have synthesized and characterized stable (non-aggregating, non-photobleaching and non-blinking), nearly monodisperse and highly-pure Au nanoparticles, and used them to probe nanoparticle transport and diffusion in cleavage-stage zebrafish embryos and to study their effects on embryonic development in real-time. We found that single Au nanoparticles (11.6 +/- 0.9 nm in diameter) passively diffused into the chorionic space of the embryos via their chorionic pore canals and continued their random-walk through chorionic space and into the inner mass of embryos. Diffusion coefficients of single nanoparticles vary dramatically (2.8 x 10(-11) to 1.3 x 10(-8) cm(2) s(-1)) as nanoparticles diffuse through the various parts of embryos, suggesting highly diverse transport barriers and viscosity gradients in the embryos. The amount of Au nanoparticles accumulated in embryos increases with nanoparticle concentration increases. Interestingly, however, their effects on embryonic development are not proportionally related to their concentration. The majority of embryos (74% on average) chronically incubated with 0.025-1.2 nM Au nanoparticles for 120 h developed to normal zebrafish, with some (24%) being dead and few (2%) deformed. We have developed a new approach to image and characterize individual Au nanoparticles embedded in tissues using histology sample preparation methods and localized surface plasmon resonance spectra of single nanoparticles. We found Au nanoparticles in various parts of normally developed and deformed zebrafish, suggesting that the random-walk of nanoparticles in embryos during their development might have led to stochastic effects on embryonic development. These results show that Au nanoparticles are much more biocompatible with (less toxic to) the embryos than the Ag nanoparticles that we reported previously, suggesting that they are better suited as biocompatible probes for imaging embryos in vivo. The results provide powerful evidences that the biocompatibility and toxicity of nanoparticles is highly dependent on their chemical properties, and that the embryos can serve as effective in vivo assays to screen their biocompatibility.

Resonant Rayleigh light scattering response of individual Au nanoparticles to antigen–antibody interaction

A proof-of-concept study was reported on analysis of antigen-antibody recognition based on resonant Rayleigh scattering response of single Au nanoparticles in an imaging chamber. As benefited by a traditional dark-field microscope and a spectrograph, individual Au nanoparticles (30 nm) were observed with high signal-to-noise ratio and they were effectively utilized to monitor changes in refractive index induced by specific binding of the adsorbates. Using PSA antigen as a model, a LSPR lambda(max) shift of about 2.85 nm was recorded for a molecular binding corresponding to 0.1 pg ml(-1) of the protein biomarker. This result successfully demonstrates a non-labeling detection system for proteins as well as thousands of different chemical or biological species, and it possesses a great potential as a sensitive, on-chip and multiplexing detection.

Probing the catalytic activity and heterogeneity of Au-nanoparticles at the single-molecule level

Nanoparticles can catalyze many important chemical transformations in organic synthesis, pollutant removal, and energy production. Characterizing their catalytic properties is essential for understanding the fundamental principles governing their activities, but is challenging in ensemble measurements due to their intrinsic heterogeneity from their structural dispersions, heterogeneous surface sites, and surface restructuring dynamics. To remove ensemble averaging, we recently developed a single-particle approach to study the redox catalysis of individual Au-nanoparticles in solution. By detecting the fluorescence of the catalytic product at the single-molecule level, we followed the catalytic turnovers of single Au-nanoparticles in real time at single-turnover resolution. Here we extend our single-nanoparticle studies to examine in detail the activity and heterogeneity of 6 nm spherical Au-nanoparticles. By analyzing the statistical properties of single-particle reaction waiting times across a range of substrate concentrations, we directly determine the distributions of kinetic parameters of individual Au-nanoparticles, including the rate constants and the equilibrium constants of substrate adsorption, and quantify their heterogeneity. Large activity heterogeneity is observed among the Au-nanoparticles in both the catalytic conversion reaction and the product dissociation reaction, which are typically hidden in ensemble-averaged measurements. Analyzing the temporal fluctuation of catalytic activity of individual Au-nanoparticles further reveals that these nanoparticles have two types of surface sites with different catalytic properties-one type-a with lower activity but higher substrate binding affinity, and the other type-b with higher activity but lower substrate binding affinity. Each Au-nanoparticle exhibits type-a behavior at low substrate concentrations and switches to type-b behavior at a higher substrate concentration, and the switching concentration varies largely from one nanoparticle to another. The heterogeneous and dynamic behavior of Au-nanoparticle catalysts highlight the intricate interplay between catalysis, structural dispersion, variable surface sites, and surface restructuring dynamics in nanocatalysis.

Aggregation Kinetics of Colloidal Particles Measured by Gas-Phase Differential Mobility Analysis

We demonstrate the utility of electrospray gas-phase ion-mobility analysis as a new method to investigate nanoparticle flocculation, or aggregation. Au nanoparticle (Au-NP) solutions were sampled via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the particle mobility distribution. Multimodal size distributions obtained with ES-DMA indicated the presence of single Au-NPs (monomer) as well as larger Au-NP clusters such as dimers, trimers, and tetramers under specific solution conditions. The fraction of each aggregate species as a function of time was quantitatively characterized, from which the degree of aggregation, aggregation rate, and stability ratio at different ionic strengths were determined. The latter enabled the extraction of a surface potential (or surface charge density) of 64 +/- 2 mV for 10 nm Au-NPs, which is in good agreement with values obtained from other methods, thus validating our approach. Our results show that ES-DMA is a valuable tool for quantitatively probing the early stages of colloidal aggregation or as a preparatory tool for the size election of aggregates.

Growth and electrical characterization of thin conductive Au nanoparticle chains on oxidized Si substrates between electrodes for sensor applications

AbstractCitrate‐stabilized colloid Au nanoparticles with an average diameter of 40 nm have been assembled in nanoparticle chains between microelectrodes on oxidized V‐groove‐etched Si surfaces by the technique of dielectrophoresis. Chain formation was investigated as a function of electrodes configuration and the amplitude and frequency of the applied electric field. Conductive thin (∼100‐200 nm thick) single and multiple Au nanoparticle chains, with a length in the range of 1 to 10 µm, were preferentially formed on V‐groove lines between the electrodes. Electrical characterization by temperature‐dependent current‐voltage measurements showed that the Au nanoparticle chains exhibit ohmic conductivity with a resistance in the range of few Ω to few kΩ, depending on the distance between electrodes and the configuration of the Au nanoparticles in the structure. On the contrary, 5 nm diameter tiopronin‐stabilized Au NPs chains exhibited nearest‐ neighbour hopping conductivity and non‐linear thermally‐activated I‐V characteristics. We also tested nanogap formation in the chains by an applied pulse of electric current, in view of applying the nanoparticle chains in the tracing of chemical or biological molecules. The conductive thin Au nanoparticle chains, with or without nanogaps, are interesting building blocks for different sensor devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of a gold nanoparticle dimer plasmonic resonator through two-phase-mediatedfunctionalization

We report that Au nanoparticles, ligand-exchanged with a thiolligand at the liquid–liquid interface, were dimerized using anN,N′-diisopropylcarbodiimide-mediated amide bond formation. This dimerization of 60 nm sizedAu nanoparticles achieved 24% overall yield and was visually confirmed by transmissionelectron microscopy as well as by scanning electron microscopy images. The resultantelectromagnetic field enhancement of a single Au nanoparticle dimer was proven by darkfield spectroscopy which, in turn, made the Au nanoparticle dimer suitable for molecularsensing applications, such as in surface enhanced Raman spectroscopy. Our dimerizationmethod demonstrated that the synthesis of Au nanoparticle dimers with a high yieldand enhanced optical properties of the dimers were possible. Our methodologyalso has good prospects as regards the formation of nanoscale building blocks.

Ultrasensitive Flow Injection Chemiluminescence Detection of DNA Hybridization Using Signal DNA Probe Modified with Au and CuS Nanoparticles

A novel and sensitive flow injection chemiluminescence assay for sequence-specific DNA detection based on signal amplification with nanoparticles (NPs) is reported in the present work. The "sandwich-type" DNA biosensor was fabricated with the thiol-functionalized capture DNA first immobilized on an Au electrode and hybridized with one end of target DNA, the other end of which was recognized with a signal DNA probe labeled with CuS NPs and Au NPs on the 3'- and 5'-terminus, respectively. The hybridization events were monitored by the CL intensity of luminol-H2O2-Cu(2+) after the cupric ions were dissolved from the hybrids. We demonstrated that the incorporation of Au NPs in this sensor design significantly enhanced the sensitivity and the selectivity because a single Au NP can be loaded with hundreds of signal DNA probe strands, which were modified with CuS NPs. The ratios of Au NPs, signal DNA probes, and CuS NPs modified on the gold electrode were approximately 1/101/103. A preconcentration process of cupric ions performed by anodic stripping voltammetry technology further increased the sensor performance. As a result of these two combined effects, this DNA sensor could detect as low as femtomolar target DNA and exhibited excellent selectivity against two-base mismatched DNA. Under the optimum conditions, the CL intensity was increased with the increase of the concentration of target DNA in the range of 2.0 x 10(-14)-2.0 x 10(-12) M. A detection limit of 4.8 x 10(-15) M target DNA was achieved.

Single-particle placement via self-limiting electrostatic gating

This letter reports single-particle placement in which exactly one nanoparticle is electrostatically guided and placed onto a target location. Using an ∼20 nm Au nanoparticle colloid as a model system, we demonstrate that self-limiting interactions between a charged nanoparticle and a charged substrate surface are extremely effective in positioning a single Au nanoparticle on each target location. Detailed theoretical calculations revealed that the self-limiting capability in the nanoparticle positioning is due to an increase in the free energy barrier after the first nanoparticle lands on a target position, effectively blocking the approach of other nanoparticles.

Detection in near‐field domain of biomolecules adsorbed on a single metallic nanoparticle

In this paper, we study the performances of nanosensors based on Localized Surface Plasmon Resonance in the context of biological sensing. We demonstrate the sensitivity and the selectivity of our designed nanosensors by studying the influence of the concentration of Streptavidin on the shift of Localized Surface Plasmon Resonance wavelength. In addition, to study the detection of biomolecules on a single Au nanoparticle, we used a Scanning Near-field Optical Microscope. These results represent new steps for applications in biological research and medical diagnostics.

A novel approach to detect and characterize the scattering patterns of single Au nanoparticles using confocal microscopy

We demonstrate a novel optical method for characterizing single Au nanoparticles by acquiring their scattering patterns. This technique combines confocal microscopy and higher-order laser modes for detecting the light scattered by sub-wavelength-sized nanoobjects. The optical patterns are generated by the coherent superposition of the field scattered by individual metallic particles and the excitation field reflected at the cover slide-air interface and provide information about the particles' position, orientation, size and shape. Detectable changes in the full width at half maximum (FWHM) of the signal intensity permit to distinguish between 20- and 60-nm diameter Au spheres. The confocal images are also very sensitive to the particle's geometry and polarizability, that is, Au nanospheres, Au nanorods and triangular Au nanoplates give different characteristic patterns if the excitation wavelength is varied.

ハイブリッド型微細加工技術を用いた金ナノ粒子の単電子トンネル効果の観測

We would like to share our recent results from a research on the single electron tunneling effect in a double-barrier tunneling junction (DBTJ) structure. Single Au nanoparticles were trapped in a nanogap electrodes, whose gap size was precisely controlled using a combination of electron beam lithography and molecular ruler technique. Here, we introduce how the novel combination technique was utilized to obtain the nanogap electrode. We also introduce the size effect of Au particles on the single electron tunneling behavior as a Coulomb island. Finally, we introduce the relation between the geometrical and electrical properties of the DBTJ.

Plasmon resonance-based optical trapping of single and multiple Au nanoparticles

The plasmon resonance-based optical trapping (PREBOT) method is used to achieve stable trapping of metallic nanoparticles of different shapes and composition, including Au bipyramids and Au/Ag core/shell nanorods. In all cases the longitudinal plasmon mode of these anisotropic particles is used to enhance the gradient force of an optical trap, thereby increasing the strength of the trap potential. Specifically, the trapping laser is slightly detuned to the long-wavelength side of the longitudinal plasmon resonance where the sign of the real component of the polarizability leads to an attractive gradient force. A second (femtosecond pulsed) laser is used to excite two-photon fluorescence for detection of the trapped nanoparticles. Two-photon fluorescence time trajectories are recorded for up to 20 minutes for single and multiple particles in the trap. In the latter case, a stepwise increase reflects sequential loading of single Au bipyramids. The nonlinearity of the amplitude and noise with step number are interpreted as arising from interactions or enhanced local fields amongst the trapped particles and fluctuations in the arrangements thereof.

Self-assembly of single thin Au nanoparticle chains on Si along V-groove-etched linesbetween micrometre-distant electrodes by dielectrophoresis

In this study we investigated the self-assembly of 40 nm size Au colloidal nanoparticles withcitrate stabilization on oxidized flat or V-groove-etched Si substrates betweenmicrometre-distant electrodes using an ac electric field and the technique ofdielectrophoresis. We demonstrated that pre-patterning of the Si surface by formingmicrometre-wide V-groove lines perpendicular to the gold electrodes facilitatessingle nanoparticle chain formation along the V-groove-etched lines. Single thin(∼100–200 nm thick) Aunanoparticle chains 1–10 µm in length were thus formed on oxidized Si between integrated electrodes. The effect of theapplied voltage and frequency of the electric field on nanoparticle chaining was investigatedin detail. The selective growth along the V-grooves was interpreted by considering theelectric field distribution between the electrodes. The samples were characterized byscanning electron microscopy and current–voltage measurements. The Au nanoparticlechains obtained were conductive and are interesting for applications in biomolecule sensing.

I - V characteristics of single electron tunneling from symmetric and asymmetric double-barrier tunneling junctions

I - V characteristics of single electron tunneling from a symmetric and an asymmetric double-barrier tunneling junction (DBTJ) were examined. A single Au nanoparticle was trapped in nanogap whose size was precisely controlled using a combination of electron beam lithography and molecular ruler technique. Though the symmetric junction showed a monotonic rise with a bias beyond the Coulomb gap voltage, the asymmetric junction showed Coulomb staircases. The capacitance of the junction estimated from the fitting curves using the Coulomb conventional theory was consistent with the capacitance calculated from the observed structure. The authors quantitatively found the correlation between the electrical and structural properties of DBTJ.

Surface enhanced infrared absorption on Au nanoparticle films deposited on SiO 2/Si for optical biosensing: Detection of the antibody–antigen reaction

The specific antibody–antigen reaction was detected by taking advantage of the effect of surface enhanced infrared absorption (SEIRA). For the SEIRA active film, single Au nanoparticles (AuNP) deposited on the SiO 2/Si wafer surface were used. After immobilizing specific antibodies onto the AuNP, these samples were then exposed to specific antigens (unspecific antigens, respectively); then the samples were investigated with infrared spectroscopy. In addition, the same kind of sample preparation was done using a 40 nm thick non-enhancing Au film, in order to compare the SEIRA transmission spectra to the infrared reflection absorption spectra (IRRAS) and therefore to determine the factor of the SEIRA enhancement. In both geometries, SEIRA transmission and IRRAS, the antibody–antigen coupling could clearly be detected; a comparison of the spectra showed, that the enhancement factor due to the Au nanoparticles is roughly 25.