In Situ Growth of Gold Nanofilms with Branched Structures in the Presence of Organosulfur for High-Performance Flexible Electronics

Herein, a novel method is presented for the in situ growth of gold nanofilms with branched structures in the presence of organosulfur. The key feature in this approach is the Rayleigh instability of ultrathin gold nanowires (AuNWs) without oleylamine (OAm), which allows the ultrathin AuNWs to decompose into gold nanoparticles (AuNPs) and the AuNPs to in situ grow into branched structures for high-performance stability and electrical conductivity. The sheet resistance of the gold nanofilms initially sharply decreased, whereas it subsequently slightly increased with the concentration of CS(NH2)2 until it exceeded the optimal range. After undergoing a 10 min heat treatment at 150 °C, the sheet resistance of the nanofilms was further reduced to 18 Ω/sq, which could be maintained for more than five months. The internal structure becomes fully grown and denser, forming a branched structure after heat treatment. Only certain organosulfurs can improve the electrical properties of the gold nanofilms, and the mechanism of organosulfur in the in situ growth of gold nanofilms with branched structures has also been presented. Overall, this novel method provides a straightforward and convenient approach to obtaining gold nanomaterials with branched structures, holding great potential promise for applications in flexible electronics, catalysis, and energy fields.

Transfection of Unmodified MicroRNA Using Monolayer-Coated Au Nanoparticles as Gene-Delivery Vehicles

This article describes a monolayer-coated gold nanoparticle-based transfection system for the delivery of microRNA (miRNA) into human osteosarcoma (HOS) cells. Two distinct ammonium-terminated adsorbates were used in this study, which provided a platform for ionic bonding of the miRNA onto gold nanoparticles (AuNPs). The custom-designed monolayer-coated gold nanoparticles were characterized by dynamic light scattering, gel mobility shift assay, transmission electron microscopy, ultraviolet-visible spectrometry, zeta potential, and X-ray photoelectron spectroscopy. The miRNA-loaded gold nanoparticles were transfected, and the level of intracellular miRNA delivered and taken up by cells was measured by Taqman qPCR. The overall analysis indicated a successful delivery of miRNA into the HOS cells at an ∼11,000-fold increase compared to nontreated cells.

Nanostructure Tuning of Gold Nanoparticles Films via Click Sintering

Colloidal metal nanoparticles dispersions are commonly used to create functional printed electronic devices and they typically require time-, energy- and equipment-consuming post-treatments to improve their electrical and mechanical properties. Traditional methods, e.g. thermal, UV/IR, and microwave treatments, limit the substrate options and may require expensive equipment, not available in all the laboratories. Moreover, these processes also cause the collapse of the film (nano)pores and interstices, limiting or impeding its nanostructuration. Finding a simple approach to obtain complex nanostructured materials with minimal post-treatments remains a challenge. In this study, a new sintering method for gold nanoparticle inks that called as "click sintering" has been reported. The method uses a catalytic reaction to enhance and tune the nanostructuration of the film while sintering the metallic nanoparticles, without requiring any cumbersome post-treatment. This results in a conductive and electroactive nanoporous thin film, whose properties can be tuned by the conditions of the reaction, i.e., concentration of the reagent and time. Therefore, this study presents a novel and innovative one-step approach to simultaneously sinter gold nanoparticles films and create functional nanostructures, directly and easily, introducing a new concept of real-time treatment with possible applications in the fields of flexible electronics, biosensing, energy, and catalysis.

Phenylalanine gold nanoclusters as sensing platform for π-π interfering molecules: a case study of iodide

The photo-physical properties of metal nano clusters are sensitive to their surrounding medium. Fluorescence enhancement, quenching, and changes in the emitted photon properties are usual events in the sensing applications using these nano materials. Combining this sensitivity with unique properties of self-assembled structures opens new opportunities for sensing applications. Here, we synthesized gold nanoclusters by utilizing phenylalanine amino acid as both capping and reducing molecule. Phenylalanine is able to self-assemble to rod-shaped nano structure in which the π-π interaction between the aromatic rings is a major stabilizing force. Any substance as iodide anion or molecule that is able to weaken this interaction influence the fluorescence of metal nano-clusters. Since the building blocks of the self-assembled structure are made through the reaction of gold ions and phenylalanine, the oxidized products and their effect of sensing features are explored.

Spin-Orbit Coupling Effects in Au 4f Core-Level Electronic Structures in Supported Low-Dimensional Gold Nanoparticles

Despite their many advantages, issues remain unresolved over the variability in catalytic activities in supported gold nanoparticle (AuNP)-based catalysts, which requires precise characterization to unravel the presence of any fine features. Herein, upon analyzing the Au 4f core-level spin-orbit components in many as-synthesized AuNP-based catalysts, we observed that like deviations in the Au 4f7/2 binding energy positions, both the Au 4f7/2-to-Au 4f5/2 peak intensity and linewidth ratios varied largely from the standard statistical bulk reference values. These deviations were observed in all the as-synthesized supported AuNPs irrespective of different synthesis conditions, variations in size, shape or morphology of the gold nanoparticles, and different support materials. On the other hand, the spin-orbit-splitting values remained almost unchanged and did not show any appreciable deviations from the atomic or bulk standard gold values. These deviations could originate due to alterations in the electronic band structures in the supported AuNPs and might be present in other NP-based catalyst systems as well, which could be the subject of future research interest.

Bimetallic Pd-Au/SiO2 Catalysts for Reduction of Furfural in Water

Catalytic systems based on bimetallic Pd-Au particles deposited on SiO2 were prepared by ultrasonically assisted water impregnation and used in the hydrogenation of furfural obtained by the acidic hydrolysis of waste biomass (brewery’s spent grain) in aqueous phase. Pd-Au/SiO2 catalysts containing 50 g of Pd and 2–100 g of Au per 1 kg of catalyst were characterized by high activity in the studied process and, depending on the Pd/Au ratio, selectivity to 2-methyloxolan-2-ol. The modification of 5%Pd/SiO2 by Au leads to the formation of dispersed Au-Pd solid solution phases, which was confirmed by XRD, XPS, ToF-SIMS, SEM-EDS, and H2-TPR techniques. The effect of dilution of surface palladium by gold atoms is probably crucial for modification of the reaction mechanism and formation of 2-methyloxolan-2-ol as the main product.

Differences in the Catalytic Behavior of Au-Metalized TiO2 Systems During Phenol Photo-Degradation and CO Oxidation

For this present work, a series of Au-metallized TiO2 catalysts were synthesized and characterized in order to compare their performance in two different catalytic environments: the phenol degradation that occurs during the liquid phase and in the CO oxidation phase, which proceeds the gas phase. The obtained materials were analyzed by different techniques such as XRF, SBET, XRD, TEM, XPS, and UV-Vis DRS. Although the metallization was not totally efficient in all cases, the amount of noble metal loaded depended strongly on the deposition time. Furthermore, the differences in the amount of loaded gold were important factors influencing the physicochemical properties of the catalysts, and consequently, their performances in the studied reactors. The addition of gold represented a considerable increase in the phenol conversion when compared with that of the TiO2, despite the small amount of noble metal loaded. However, this was not the case in the CO oxidation reaction. Beyond the differences in the phase where the reaction occurred, the loss of catalytic activity during the CO oxidation reaction was directly related to the sintering of the gold nanoparticles.

Gold Decoration and Photoresistive Response to Nitrogen Dioxide of WS2 Nanotubes

Composites of WS₂ nanotubes (NT-WS₂ ) and gold nanoparticles (AuNPs) were prepared using aqueous HAuCl₄ solutions and subjected to surface analysis. The obtained materials were jointly characterized by X-ray photoelectron (XPS), Raman scattering (RSS), and ultraviolet photoelectron (UPS) spectroscopies. Optical extinction spectroscopy and electron energy loss spectroscopy in the scanning transmission electron microscopy regime (STEM-EELS) were also employed to study plasmon features of the nanocomposite. It was found that AuNPs deposition is accompanied by a partial oxidative dissolution of WS₂ , whereas Au-S interfacial species could be responsible for the tight contact of metal nanoparticles and the disulfide. A remarkable sensitivity of n-type resistance of NT-WS₂ and Au-NT-WS₂ to the adsorption of NO₂ gas was also demonstrated at room temperature using periodical illumination by a 530 nm light-emitting diode. Au-NT-WS₂ nanocomposites are found to possess a higher photoresponse and enhanced sensitivity in the 0.25-2.0 ppm range of NO₂ concentration, as compared to the pristine NT-WS₂ . This behaviour is discussed within the physisorption-charge transfer model to explore sensing properties of the nanocomposites.

Simple, low-cost, sensitive and label-free aptasensor for the detection of cardiac troponin I based on a gold nanoparticles modified titanium foil

This research demonstrated the electrochemical modification of low-cost titanium (Ti) metal substrate with gold nanoparticles (AuNPs) for the aptamer-based detection of cardiac troponin I (cTnI). AuNPs were deposited onto Ti sheets by the potential-step deposition method with high density and homogeneity as well as good crystallinity. It was then applied as a transducer to immobilize a thiol-functionalized DNA aptamer via the self-assembled monolayer mechanism for the specific binding of cTnI. This was verified through electrochemical and morphological analyses. The aptasensor could detect cTnI in a linear range of 1-1100 pM with a detection limit of ca. 0.18 pM. The aptasensor showed high sensitivity and specificity to cTnI over other interfering compounds with good recoveries in the diluted human serum samples.

Au-Si plasmonic platforms: synthesis, structure and FDTD simulations

Plasmonic platforms based on Au nanostructures have been successfully synthesized by directional solidification of a eutectic from Au and the substrate. In order to determine homogeneous shape and space distribution, the influence of annealing conditions and the initial thickness of the Au film on the nanostructures was analyzed. For the surface morphology studies, SEM and AFM measurements were performed. The structure of platforms was investigated using XRD and XPS methods. Structural investigations confirmed, that nanostructures consist of metallic Au, growing along the [111] direction. The most homogeneous seems to be the platform obtained by solidification of a 2.8 nm Au film, annealed at 550 °C for 15 min. This sample was subsequently chosen for theoretical calculations. Simulations of electromagnetic field propagation through the produced samples were performed using the finite-difference time domain (FDTD) method. The calculated absorbance, as a result of the FDTD simulation shows a quite good agreement with experimental data obtained in the UV-vis range.

Impact of Nonideal Nanoparticles on X-ray Photoelectron Spectroscopic Quantitation: An Investigation Using Simulation and Modeling of Gold Nanoparticles

Quantitative X-ray photoelectron spectroscopic (XPS) analysis combined with spectral modeling of photoelectrons can be valuable while investigating the surface chemistry of nanoparticles (NPs) with different morphologies. Herein, with the use of NIST Simulation of Electron Spectra for Surface Analysis (SESSA), a comparative analysis of experimental and simulated photoelectron peak intensities in gold nanoparticles (AuNPs) of different morphologies is presented. Three sets of supported AuNPs with different morphologies were selected from a series of as synthesized Au-TiO₂ catalyst samples. Using transmission electron microscopy (TEM) analyzed morphological information on the AuNPs as input model parameters in SESSA, XPS spectra were generated from the respective input NP morphologies. A degree of greater mismatch between SESSA simulated and experimental XPS spectra was observed while using the TEM obtained average diameter of the nanoparticles. The degree of mismatch lowered when the true nonspherical shape of the nanoparticles as obtained from TEM images was taken into account for the simulation. This demonstrates the impact of surface morphology on the XPS peak intensities which needs to be incorporated to obtain precise quantified information from the supported nanoparticles. This work demonstrates the applicability of SESSA in combination with experimental XPS and TEM measurements for precise quantification of XPS spectra from complex, nonideal shaped nanoparticles. This study can be extended to include a broad range of nanoparticles with ideal or nonideal geometries, thus providing a simple method to utilize quantitative XPS analysis to a wide range of nanomaterials.