XPS study of interactions between linear carbon chains and colloidal Au nanoparticles

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Corrosion of Au particles in air-exposed NaI-treated Au colloidal suspensions

This study examines the influence of the treatment of citrate-capped Au colloidal particles with NaI under exposure to air. Whereas in the NaI-treated centrifugate of the Au colloidal suspension the iodide-induced formation of triiodide runs spontaneously, its accumulation is found to be strongly decelerated in the Au colloidal suspension under the same conditions. In accordance with the experimental findings from electron absorption spectroscopy and transmission electron microscopy, a mechanism is proposed which describes the oxidation of the Au particles by oxygen under intermediate participation of triiodide.     

Synthesis of colloidal silver nanoparticles for printed electronics

Colloidal silver particles were successfully prepared by wet chemical synthesis. The pure single phase of silver was confirmed by X-ray diffraction. Transmission electron microscope categorized that the diameters of particles were 100 and 20 nm, depending on the molecular weight of the PVP stabilizer. A schematic drawing model was used to predict the packing efficiency of 1:1 wt% of two mixtures. The mixture of silver solution was deposited as a thin solid film by a desktop inkjet printer. Scanning electron microscope showed that two different sizes of silver particles give higher densely packed structure than the film of single particle size. When a 0–20 V voltage was applied, the current density reached was 0.10 J/cm², suggesting that the silver film has potential to be applied as a cathode layer in organic light emitting diode (OLED) devices.     

Shell cross-linked Au nanoparticles

The organic layer of thiol-protected Au nanoparticles (ca.3 nm in diameter) was cross-linked using ring-opening metathesis polymerization or Michael addition of polyfunctional amines. The shell cross-linked nanoparticles showed increased stability toward thermal treatment and oxidative etching. The Au core of cross-linked nanoparticles was removed in an attempt to prepare hollow capsules. However, Au etching resulted in insoluble materials.     

Micropatterns constructed from Au nanoparticles

Covalently linked Au-NPs micropatterns have been successfully fabricated from the self-assembly film composed of 4-mercaptophenol-capped Au nanoparticles (Au-NPs) and -N2+ containing polymers of nitro-diazoresin (NDR) by selective exposure to UV light and development in sodium dodecyl sulfate (SDS) aqueous solution. The resultant well-defined micropatterns were characterized with AFM and XPS.     

Application of colloidal palladium nanoparticles for labeling in electron microscopy

The application of palladium nanoparticles as electron-dense markers for labeling in both transmission and scanning electron microscopy requires their conjugation to a specific protein. The conjugation protocol described here includes the dihydrolipoic acid (DHLA) capping of Pd nanoparticles (8 nm equivalent diameter) and their subsequent covalent attachment to functional protein molecules such as streptavidin, protein A, or avidin. The single-step reaction was mediated using the cross-linking agent ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The final Pd conjugates were fully functional, as demonstrated by labeling of ultrathin resin sections of either bovine serum albumin or secretory granules of the salivary gland isolated from the partially fed female Ixodes ricinus tick. The results of bovine serum labeling were quantified, statistically evaluated, and compared with results obtained using commercially available gold particle conjugates (10 nm diameter). The highest values of labeling density were achieved using both streptavidin-Pd (106 ± 7 particles/μm2) and protein A-Au conjugates (130 ± 18 particles/μm2) compared to a commercial streptavidin-Au (66 ± 16 particles/μm2) and protein A-Pd conjugates (70 ± 11 particles/μm2). The concentrations of both DHLA and EDC, pH during conjugation, and finally thorough washing away of unbound proteins crucially influenced conjugation.     

Nanoporous Ge coated by Au nanoparticles for electrochemical application

We present an innovative device based on a nanoporous Ge electrode decorated by gold nanoparticles (AuNPs). A study aimed at obtaining the best AuNP deposition conditions, which allow the decoration of Ge walls with AuNPs, avoiding particles aggregation is reported.The performance of the electrode has been evaluated by the electrocatalytic reduction of iodoethane in acetonitrile solution, a model reaction in organic electrocatalysis.     

Au nanoparticles as a novel coating for solid-phase microextraction

A novel solid-phase microextraction fiber based on a stainless steel wire coated with Au nanoparticles was prepared and has been applied, coupled with gas chromatography, to the extraction of aromatic hydrophobic organic chemical pollutants in rainwater and soil extract. The solid-phase microextraction fiber exhibited excellent extraction efficiency and selectivity. Effects of extraction time, extraction temperature, ionic strength, stirring rate and desorption conditions were investigated and optimized. Single fiber repeatability and fiber-to-fiber reproducibility were less than 7.90% and 26.40%, respectively. The calibration curves were linear in a wide range for all analytes. Correlation coefficients ranged from 0.9941 to 0.9993. The as-established SPME-GC method was used successfully to two real natural samples. Recovery of analytes spiked at 10 μg L(-1) and 100 μg L(-1) ranged from 78.4% to 119.9% and the relative standard deviations were less than 11.3%.     

Electrochemical behavior of Au colloidal electrode through layer-by-layer self-assembly

Electrodes formed by Au colloidal nanoparticles have been obtained by layer-by-layer self-assembly using 1,6-hexanedithiol as cross-linkers. Cyclic voltammograms show that the peak-to-peak separation decreases as the number of Au colloidal layers increases. After seven layers of Au colloidal particles have been deposited, the multilayer electrodes have the electrochemical properties of metallic Au and show ideal microelectrode behavior. An equivalent circuit for the electrochemical impedance spectroscopy was established to model the working electrode. It is evident that by increasing the layer number of Au colloidals, the interfacial electron transfer is promoted, implying the electron-transfer process changes from a kinetically limited process to a diffusionally limited process.     

Self-assembled colloidal crystals from ZrO2 nanoparticles

Ordered three-dimensional (3-D) assemblies of nanocrystalline zirconia were synthesized from aqueous suspensions of ZrO(2) nanoparticles without the need for hydrocarbon surfactants or solvents to control colloidal crystal growth. Nanoparticles were suspended in mild acid and subsequently titrated from low to neutral pH. The solubility was reduced as the surfaces were neutralized, promoting assembly of the nanoparticles into ordered monoliths. TEM measurements indicated the formation of three-dimensional, hexagonal faceted, micrometer-sized colloidal crystals composed of 4 nm diameter ZrO(2) nanoparticles. Lacking organic surfactants, the colloidal crystals were exceptionally robust and were sintered at high temperatures (300-500 degrees C) for further stability. Small-angle X-ray scattering (SAXS) measurements demonstrate that the samples become progressively more amorphous above 350 degrees C, although some ordered domains of nanoparticles persist. Additionally, the heat treatment dramatically increases the surface area of the colloidal crystals as water and residual organics are desorbed, revealing highly controlled interstitial spaces and pores.     

Macroporous Au materials prepared from colloidal crystals as templates

In this paper, we reported the preparation of macroporous Au materials using organic colloidal crystals as templates and their catalytic activity for electroless copper deposition. The poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) copolymer colloids were deposited in an orderly manner onto the silicon surface, together with the infiltration of the Au nanoparticles into the interspaces of the colloids. The formed hybrid colloidal crystal subsequently was sintered at approximately 550 degrees C to remove the organic components fully to obtain a macroporous Au framework with three-dimensional ordered porous structure. The pore diameter was around 310 nm and almost monodisperse. It was demonstrated that the macroporous Au materials exhibit catalytic activity and can induce electroless copper deposition.     

Synthesis of small-sized rhenium sulfide colloidal nanoparticles

Rhenium sulfide colloidal nanoparticles with average size 5.5 nm were synthesized. Characterizations by ultraviolet-visible spectrophotometry, transmission electron microscopy, energy dispersive X-ray spectrum, and X-ray powder diffraction verified the formation of ReS(2) rhenium sulfide colloidal nanoparticles. The colloidal nanoparticles had good stability and they could be stored stably for 1 week in water. Surface modification by organic molecules improved the stability of the rhenium sulfide nanoparticles. The small-sized rhenium sulfide nanoparticles may be useful for their promising applications in tracing diagnosis and therapy of tumor diseases.     

Electrophoretic properties of DNA-modified colloidal gold nanoparticles

Oligonucleotide-modified gold nanoparticles are used in various kinds of colorimetric DNA targeting biosensors and nanoparticle assembly techniques. Herein we focus on how the size of 13 nm gold colloids changes upon DNA modification. We have performed a series of electrophoresis experiments of particles modified both thiol specifically and nonspecifically with single- and double-stranded oligonucleotides of different lengths (12- and 25-mers). Both unmodified and DNA-modified particles migrated at constant velocity in different concentrations of Metaphor agarose gels. Linear Ferguson plots were obtained for all samples, and on the basis of the Ogston model approach, we present how the particle size increases in different amounts depending on the oligonucleotide length, secondary structure, and type of modification (specific or nonspecific). Thiol specifically modified particles obtain a thicker DNA layer since the oligonucleotides are only anchored to the particle in one end and thus stand up from the surface more compared to nonspecifically modified ones, where the oligonucleotides tend to lay more or less flat on the surface with multiple adsorption points. However the thickness of the DNA layer for the thiol specifically modified particles is smaller than the length of a corresponding stretched oligonucleotide, suggesting a flexibility of the thiol-bound strands allowing them to tilt relative to the particle surface.     

Surface chemistry of luminescent colloidal silicon nanoparticles

Luminescent colloidal silicon particles are obtained by burning silane and slowly etching the product with hydrogen fluoride. Depending on their size, the particles emit red-orange or blue-green light with decay times between 28 micros and <0.1 micros, respectively. The quantum yield of the red luminescence is found to be 35%, i.e., much higher than the 7% previously reported, and the yield of the blue-green luminescence is 18%. The luminescence of the colloidal particles is quenched upon the attack of their surface by free radicals, oxygen-centered radicals being more efficient than carbon-centered ones. It is concluded from the dependence of the luminescence wavelength on the etching time and the dependence of the luminescence lifetime on the wavelength that the mechanism of the photoluminescence undergoes a change with decreasing particle size. The red luminescent particles exhibit amphiphilic properties, such as unusual wetting phenomena. This effect is understood in terms of the existence of few polar groups on the otherwise nonpolar surface of the particles, possibly Si-OH groups, which also act as centers of the red luminescence.     

DNA-embedded Au/Ag core-shell nanoparticles

Here, we synthesized highly stable DNA-embedded Au/Ag core-shell nanoparticles (NPs) by a straightforward silver-staining of DNA-modified Au nanoparticles (AuNPs); unlike conventional DNA-surface modified NPs that present particle stability issues, DNA-embedded core-shell NPs offer an extraordinary stability with nanoscale controllability of silver shell thickness; these DNA-embedded core-shell NPs show excellent biorecognition properties and Ag shell-thickness-based optical properties, distinctively different from those of a mixture of AuNPs and AgNPs or Ag/Au alloy nanoparticles.     

Theoretical analysis of methods for the colloidal synthesis of monodisperse nanoparticles

Methods for the colloidal synthesis of monodisperse nanoparticles, in which the interrelated processes of nucleation and growth of nanoparticles occurring with variable supersaturation of the solution play a determining role, have been theoretically analyzed. It is supposed that supersaturation is created as a result of a chemical reaction; two reactant feed modes (instantaneous and regularly time-distributed) are considered. Successive steps of growth have been distinguished and described for each mode. Conditions at which the focusing mechanism of the particle-size distribution function is operative are specified.     

Polymer coatings for sensitive analysis of colloidal silica nanoparticles in water

A new analytical approach has been developed for the sensitive detection of trace nanomaterials in water using silica as model inorganic nanoparticles. Our novel approach is based on coating of the nanoparticles with a polymer to make them larger in size for better ultraviolet (UV) light absorption. These polymer-coated nanoparticles can be separated from the monomer and polymer by capillary electrophoresis (CE) due to differences in their ionic charge, size, and surface functionality. Controlled polymerization of 2-hydroxypropyl methacrylate (HPMA) on silica nanoparticles increased their UV detection sensitivity by 5–7-fold. A second coating with polydopamine produced an extra 2-fold increase of the UV detection sensitivity. With both polyhydroxypropyl methacrylate and polydopamine coatings, a significant total enhancement of 10–14-fold in detection sensitivity was attained. Alternatively, addition of bisphenol A or polyvinyl alcohol to the HPMA polymerization mixture resulted in 9–10-fold increase of SiO₂ detection sensitivity due to additional absorption of the UV detector light.     

Non aggregated colloidal silver nanoparticles for surface enhanced resonance Raman spectroscopy

Silver nanoparticles with a tuneable λ max were produced as colloids by heterogeneous nucleation. The synthesis process is both fast and repeatable, producing stable PVA capped nanoparticles. The colloid's effectiveness in the SERRS system was investigated using Rhodamine 6G, R6G, Crystal Violet, CV, and Malachite Green, MG, as probe molecules. A clear sensing trend was observed, where the Raman signal emitted was significantly enhanced by the addition of silver nanoparticles. A build up of signal intensity is observed until an optimum ratio is achieved, followed by a decline in signal intensity as the concentration of nanoparticles is further increased. The sensing trend appeared to be dependant on the structure of these model molecules with similarly structured compounds exhibiting similar trends. Thus a maximum enhancement with the Ag: analyte molar ratio of ～ 5.56: 1, was seen for CV and MG whereas R6G had a maximum enhancement at the Ag: analyte molar ratio of ～ 2.25: 1.