Gold-coated Silver Research Articles

Enhancing the anti-tarnish and mechanical properties of gold-coated silver sheets for decorative applications using TiO2 film protection

This study explores an innovative method to enhance the anti-tarnish and mechanical properties of gold-coated silver sheets, targeting decorative applications through the TiO2 film coatings. The research focuses on gold films with a thickness of approximately 100 nm, and TiO2 films ranging from 10 to 31 nm. It was observed that the color of the multilayer coatings exhibited significant sensitivity to variations in thickness, indicating that a TiO2 coating with a thickness around 20 nm could be optimally applied to the gold film, maintaining an acceptable ΔE value. X-ray photoelectron spectroscopy analysis demonstrated the TiO2 film’s potential to inhibit the formation of Ag2S on the surface, thereby enhancing tarnish resistance. Furthermore, the application of a 20 nm TiO2 layer reduced the friction coefficient from 0.28 to 0.24 for gold-coated silver. Durability tests involving 1,000 abrasion cycles revealed that the gold film without TiO2 protection experienced delamination, with only about 57 % of the coated area remaining intact. In contrast, the samples protected with a TiO2 layer retained approximately 90 % of the coating, underscoring the effectiveness of TiO2 in preserving the structural integrity and appearance of the gold-coated silver sheets.

Porous silica-based platform bearing Au/Ag nanosheets for targeted combination therapy and fluorescence imaging

A versatile delivery platform combining gold-coated silver triangular nanosheets (Ag@Au NSs) and silver sulfide (Ag2S) quantum dots (QDs) embedded porous silica (Ag2S/pSiO2) carriers was developed for combination therapy and fluorescence imaging. The Ag@Au NSs exhibited excellent biocompatibility and photothermal efficiency. After combining the Ag2S/pSiO2 carriers with Ag@Au NSs (Ag2S/pSiO2/Ag@Au), a high drug loading rate of 25.48 % for doxorubicin hydrochloride (DOX) was attained. After loading DOX, Ag2S/pSiO2/Ag@Au was coated with hyaluronic acid (HA) (DOX-Ag2S/pSiO2/Ag@Au/HA), which could target CD44 receptors that are overexpressed in cancer cells. The Ag@Au NSs maintained the impressive surface plasmon resonance (LSPR) of Ag NSs, enabling them to function as SERS substrate. During DOX release, the released DOX was detected through Raman technique. The Ag2S/pSiO2/Ag@Au/HA system demonstrated excellent performance in thermo-chemotherapy and allowed visualization of drug release behavior and vector imaging using Raman and fluorescence imaging technologies. These results demonstrated the potential of the Ag2S/pSiO2/Ag@Au/HA system as an effective carrier for therapeutic application.

Triangular Silver Nanoplates as a Bioanalytical Tool: Potential COVID-19 Detection.

Nanotechnology offers new possibilities in molecular diagnostics, with nanoparticles gaining attention as biosensor upgrades. This study evaluates gold-coated silver nanoplates coated with PEG for enhanced protection, aiming to detect Spike protein with higher sensitivity, and emphasizes the importance of considering complex environments and appropriate controls for specific binding and accurate analysis. The sensitivity of antibody-coated PEGAuTSNPs as tools for immunoassays is demonstrated through fibronectin (Fn)- anti-fibronectin binding within an isolated extracellular matrix as a complex and native environment of Fn. Moreover, the optimal functionalization volume of Spike protein was determined (4 µg/mL of PEGAuTSNP). Anti-Spike was added to confirm binding, while the TJP1 protein was used as a negative control. The same experiment was used in the presence of horse serum to simulate a complex environment. According to Localized Surface Plasmon Resonance analysis and Dynamic Light Scattering size measurements, anti-Spike exhibited a stronger affinity for the nanoplates, causing TJP1 to be replaced by the antibody on the nanoplates' surface. Future research will involve exploring alternative complex environments, filtering larger molecules, and the optimization of immunoassay performance.

Transparent and Stretchable Au─Ag Nanowire Recording Microelectrode Arrays.

Transparent microelectrodes have received much attention from the biomedical community due to their unique advantages in concurrent crosstalk-free electrical and optical interrogation of cell/tissue activity. Despite recent progress in constructing transparent microelectrodes, a major challenge is to simultaneously achieve desirable mechanical stretchability, optical transparency, electrochemical performance, and chemical stability for high-fidelity, conformal, and stable interfacing with soft tissue/organ systems. To address this challenge, we have designed microelectrode arrays (MEAs) with gold-coated silver nanowires (Au─Ag NWs) by combining technical advances in materials, fabrication, and mechanics. The Au coating improves both the chemical stability and electrochemical impedance of the Au─Ag NW microelectrodes with only slight changes in optical properties. The MEAs exhibit a high optical transparency >80% at 550 nm, a low normalized 1 kHz electrochemical impedance of 1.2-7.5 Ω cm2, stable chemical and electromechanical performance after exposure to oxygen plasma for 5 min, and cyclic stretching for 600 cycles at 20% strain, superior to other transparent microelectrode alternatives. The MEAs easily conform to curvilinear heart surfaces for colocalized electrophysiological and optical mapping of cardiac function. This work demonstrates that stretchable transparent metal nanowire MEAs are promising candidates for diverse biomedical science and engineering applications, particularly under mechanically dynamic conditions.

Electrocatalytic Reduction of Aldonic Acids to Aldoses on Gold Electrodes

Spent sulfite liquor, a side-stream from the pulp and paper industry, is an abundantly available carbon source for bio-based platform chemicals. The biotechnological valorization of side streams in biorefineries is hampered by the inability of many microorganisms to metabolize and deal with aldonic acids. Based on the principles of Green Chemistry, the electrochemical reduction of aldonic acids into the corresponding biomass sugars appears as a prospective process for the conversion of these acids into fermentable carbohydrates. In our paper, the investigation of electrochemical reduction of gluconic and xylonic acids into glucose and xylose, respectively, is presented. The proposed mechanism on a gold-coated silver electrode was determined via ReaxFF molecular dynamics simulations and quantum chemistry calculations. Model solutions with an aldonic acid concentration of 2.5 wt % were used for the experiments. Compared to a two-electrode compartment cell, the amounts of glucose and xylose produced in the undivided cell were more than 4 and 5.5 times higher, respectively. The electrode surface was analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Despite the relatively low conversion rate, our results show that electrochemical reduction of aldonic acids into their corresponding aldoses in model solutions is possible, which represents an important step toward side-stream valorization.

Length-Controllable Gold-Coated Silver Nanowire Probes for High AFM-TERS Scattering Activity.

Tip-enhanced Raman scattering (TERS) microscopy is an advanced technique for investigation at the nanoscale that provides topographic and chemical information simultaneously. The TERS probe plays a crucial role in the microscopic performance. In the recent past, the development of silver nanowire (AgNW) based TERS probes solved the main tip fabrication issues, such as low mechanical strength and reproducibility. However, this fabrication method still suffers from low control of the protruded length of the AgNW. In this work, a simple water-air interface electrocutting method is proposed to achieve wide controllability of the length. This water cutting method was combined with a succedent Au coating on the AgNW surface, and the probe achieved an up to 100× higher enhancement factor (EF) and a 2× smaller spatial resolution compared to pristine AgNW. Thanks to this excellent EF, the water-cut Au-coated AgNW probes were found to possess high TERS activity even in the nongap mode, enabling broad applications.

Morphology-regulated core–shell Ag@Au NPs for rapid SERS detection of 1-amino-hydantoin (AHD) in crayfish

ABSTRACT Gold-coated silver core–shell nanoparticles (Ag@Au NPs) have been widely used for SERS analysis due to plasmon resonance performances. However, it is a great challenge to fabricate Ag@Au core–shell structures with specified morphology. In this paper, the size and shape of Ag NPs (core) were precisely controlled by a seed-mediated approach, and then the gold shell was completely coated on under the strong reduction of ascorbic acid, resulting in Ag@Au NPs with highly regulated morphology. The obtained Ag@Au NPs achieved a similar or even better SERS enhancement factor (EF) (up to 5.7 × 107) compared to Ag NPs, but significantly higher stability. For the rapid SERS detection of nitrofurantoin metabolite AHD, a limit of detection (LOD) as low as 1 × 10−10 M and a wide linear range from 1 × 10−4 to 1 × 10−8 M were obtained. Furthermore, recoveries for crayfish samples were from 90.5% to 108%, indicating a good performance of the presented method in real sample detection.

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules.

A zeroth-order, non-diffracting Bessel beam, generated by picosecond laser pulses (1064 nm, 10 Hz, 30 ps) through an axicon, was utilized to perform pulse energy-dependent (12 mJ, 16 mJ, 20 mJ, 24 mJ) laser ablation of silver (Ag) substrates in air. The fabrication resulted in finger-like Ag nanostructures (NSs) in the sub-200 nm domain and obtained structures were characterized using the FESEM and AFM techniques. Subsequently, we employed those Ag NSs in surface-enhanced Raman spectroscopy (SERS) studies achieving promising sensing results towards trace-level detection of six different hazardous materials (explosive molecules of picric acid (PA) and ammonium nitrate (AN), a pesticide thiram (TH) and the dye molecules of Methylene Blue (MB), Malachite Green (MG), and Nile Blue (NB)) along with a biomolecule (hen egg white lysozyme (HEWL)). The remarkably superior plasmonic behaviour exhibited by the AgNS corresponding to 16 mJ pulse ablation energy was further explored. To accomplish a real-time application-oriented understanding, time-dependent studies were performed utilizing the AgNS prepared with 16 mJ and TH molecule by collecting the SERS data periodically for up to 120 days. The coated AgNSs were prepared with optimized gold (Au) deposition, accomplishing a much lower trace detection in the case of thiram (~50 pM compared to ~50 nM achieved prior to the coating) as well as superior EF up to ~108 (~106 before Au coating). Additionally, these substrates have demonstrated superior stability compared to those obtained before Au coating.

Picosecond Bessel Beam Fabricated Pure and Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules

Picosecond Bessel Beam Fabricated Pure and Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules

Ultrasonic Bonding Interface Degradation Characteristics of Gold-Coated Silver Wire for Semiconductor Packaging

Gold-coated silver wire was developed to alleviate the high cost of Au wire used in semiconductor packaging. Ball-bonding and stitch-bonding techniques were used to fabricate the dummy packaging material, comprising 97.3 % Ag, 97.3% Au-Coated Ag, and 99.99 %Au wires. The wire ball shear test (BST), the wire ball pull test (BPT), and the microstructural attributes of the ultrasonic bonding interfaces were compared with the initial properties, both before and after the highly accelerated stress test (HAST), conducted at 130 ℃ and 85% relative humidity (RH). The initial bonding strength for all the wire variants was ?23~24 gf. Following the HAST, the bonding strength of the Ag wire, the Au-coated Ag wire, and the Au wire decreased by approximately 75 %, 47 %, and 17 %, respectively. The microstructure analysis revealed that cracks developed and propagated at the ends of the interface and that the Au-rich Au-Al intermetallic compound (IMC) inhibited the propagation of the crack at the ACA/Au wire interface. Additionally, it was discovered that the presence of the Ag-Au-Al IMC at the interface of the ACA wire reduced Kirkendall voids, which act as a barrier to Au-Al interdiffusion.

Multiplex Electrochemiluminescence Polarization Assay Based on the Surface Plasmon Coupling Effect of Au NPs and Ag@Au NPs.

A novel multiplex electrochemiluminescence (ECL) polarization assay was developed to detect breast cancer-related genes BRCA1 and BRCA2 simultaneously based on the polarization characteristics of surface plasmon-coupled electrochemiluminescence (SPC-ECL). In this work, boron nitride quantum dots (BN QDs) were used as ECL emitters, and gold nanoparticles (Au NPs) and gold-coated silver nanoparticles (Ag@Au NPs) were employed as surface plasmon materials. The surface plasmon coupling resonance of different metal NPs not only enhanced the ECL intensity but also converted the isotropic emission into directional emission. This study revealed the relation between the structure of metal nanomaterials and SPC-ECL, and a high polarization-resolved sensing system was designed to detect multitarget DNA from 100 aM to 1 nM simultaneously. Polarization-based multiple ECL analysis has broad prospects in related cancer diagnosis and treatment evaluation.

Construction of Boronate-Affinity Magnetic Immunity SERS Sensor and Detection of Alpha-Fetoprotein (AFP) in Human Serum

Abstract According to its characteristics, borate can recognize and adsorb target glycoproteins and specific binding properties of antigens and antibodies. This article introduces a preparation method for a magnetic immune SERS sensor, and it is used for the specific identification and detection of trace AFP in human serum. The test used AFP as the target protein and 4-mercaptophenylboronic acid (4-MPBA) modified gold-coated silver nanoparticles (Ag@AuNPs) as the signal factor. After the AFP antibody was grafted on the boric acid group, the SERS detection probe (Ag@Au@4-MPBA@Anti-AFP) was obtained. On the surface of boric acid-functionalized (-P) magnetic silica particles, AFP antibody was modified, and the particles were used as magnetic immunocapture probes (Fe3O4@SiO2-P@Anti-AFP). Finally, the sandwich structure complex of “detection probe-target protein-capture probe” was successfully constructed. The prepared magnetic immune SERS sensor exhibits excellent selectivity and high sensitivity for AFP detection; based on the signal-to-noise ratio S/N = 3, the detection limit can reach 1.0 ng/mL; by performing a spike test on AFP in human serum, the sensor can be used to detect AFP in actual samples. The recovery rate was between 85.8% and 105.7%, and the RSD distribution was ≤3.52%. The sensor was easy to prepare, required no complex processing of samples and can achieve rapid detection, so that it is expected to become a new strategy for clinical detection of AFP.

Drug Release System Controlled by Photothermal Effect of Gold Nanoparticles

Controlled drug release in response to light irradiation is an important technique for focusing drug elution to specific sites and reducing the side effects of drugs in normal tissue. In one example, we used double-stranded DNA to modify gold nanorods. When the gold nanorods were heated by irradiation with near-infrared light, single-stranded DNA was released. Thus, we successfully prepared a controlled release system that responds to near-infrared irradiation by combining heat-labile linkers such as double-stranded DNA. However, the drug-loading capacity on the surface of the nanoparticles was limited. To improve the loading efficiency, we encapsulated gold nanorods in poly(lactic-co-glycolic acid) (PLGA) nanoparticles, where PLGA acted as a drug payload. When the gold nanorod-containing PLGA nanoparticles were irradiated with a near-infrared laser, the PLGA nanoparticles were destroyed and significant drug release was observed. In another example, silver nanoplates were used as a near-infrared responsive photothermal nanodevice. Silver nanoparticles show antimicrobial activity that we expected could be controlled by light irradiation. First, we coated the silver nanoplates with gold atoms to mask the antimicrobial activity. When the gold-coated silver nanoplates were irradiated with a near-infrared pulsed laser, the shape of the silver nanoplates changed from plate-like to spherical, and silver ions were released. As a result, the antibacterial activity of the silver nanoplates was recovered. In this review, we outline examples of controlled release systems that respond to light irradiation. We believe that this review will contribute to improving the efficiency and safety of chemotherapy.

Gold-coated silver capsule for elemental analyzer-isotope ratio mass spectrometer: Robust against pretreatment of rock material for organic carbon and δ<sup>13</sup>C analyses

Gold-coated silver capsule for elemental analyzer-isotope ratio mass spectrometer: Robust against pretreatment of rock material for organic carbon and δ<sup>13</sup>C analyses

Low-Cytotoxic Gold-Coated Silver Nanoflowers for Intracellular pH Sensing

Intracellular pH affects many biological processes such as apoptosis, proliferation, endocytosis, and multidrug resistance. In view of this, highly sensitive pH sensing in live cells is essential f...

Highly conductive, stretchable and biocompatible Ag-Au core-sheath nanowire composite for wearable and implantable bioelectronics.

Wearable and implantable devices require conductive, stretchable and biocompatible materials. However, obtaining composites that simultaneously fulfil these requirements is challenging due to a trade-off between conductivity and stretchability. Here, we report on Ag-Au nanocomposites composed of ultralong gold-coated silver nanowires in an elastomeric block-copolymer matrix. Owing to the high aspect ratio and percolation network of the Ag-Au nanowires, the nanocomposites exhibit an optimized conductivity of 41,850 S cm-1 (maximum of 72,600 S cm-1). Phase separation in the Ag-Au nanocomposite during the solvent-drying process generates a microstructure that yields an optimized stretchability of 266% (maximum of 840%). The thick gold sheath deposited on the silver nanowire surface prevents oxidation and silver ion leaching, making the composite biocompatible and highly conductive. Using the nanocomposite, we successfully fabricate wearable and implantable soft bioelectronic devices that can be conformally integrated with human skin and swine heart for continuous electrophysiological recording, and electrical and thermal stimulation.

Employment of gold-coated silver nanowires as transparent conductive electrode for organic light emitting diodes

This study proposes a simple method of Au coating on silver nanowires (Ag NWs) transparent conductive films as the anode of organic light emitting diodes (OLED) to increase the work function of the film and thus enhance hole transport. We carefully engineer the process conditions (pretreatment, solution concentrations, and coating number) of the coating using a diluted HAuCl4 solution on the Ag NWs film to minimize etching damage on Ag NWs accompanying the galvanic replacement reaction. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy show work function increase of Ag NWs upon Au coating. OLED devices based on Au-coated Ag NWs show a lower turn-on voltage and higher luminance, compared with pristine Ag NWs device. Although the Ag NWs device displays poor efficiencies in the low luminance range due to a high leakage, some of the Au-coated Ag NWs devices showed efficiencies higher than those of the ITO device in a high luminance.

Zinc Oxide Nanorod Growth on Au-coated Silverwire

In this study, zinc oxide nanostructures were grown on gold-coated silver wires by hydrothermal method. Multiple analyses on these nanostructures were performed to understand the structure and optical properties of zinc oxide on Au-plated silver wires, Owing to the Au-coated layer, ZnO nanorods could appear rather than ZnO nanoflakes on pure silver wires. Moreover, The deposited gold layer could vary zinc oxide nanostructures to nanorods The multiple analysis shows that lying flat ZnO structures with weak (002) crystalline structures and more defects could appear on the silver wire rather than ZnO nanostructures on pure silver wires.

Effects of pulsed laser irradiation on gold-coated silver nanoplates and their antibacterial activity.

Gold-coated silver nanoplates, when subjected to pulsed laser irradiation, changed their shape from triangular to spherical, accompanied by a shift of their extinction spectra. The simple single crystal structure of the silver nanoplates changed to multiple small crystal domains. The ratio of silver to gold of the particles also changed from 22 : 1 to 4.5 : 1, enabling more silver to be released. As a result, the antibacterial activity of the gold-coated silver nanoplates was significantly increased after pulsed laser irradiation.

Importance of Tilt Angles of Adsorbed Aromatic Molecules on Nanoparticle Rattle SERS Substrates

Solution-phase nanoparticles are extensively used as surface enhanced Raman scattering (SERS) substrates, but signal intensities depend on dynamic nanoparticle optical properties and stabilities as well as molecular identity and orientation. To evaluate how these contributions influence the detection of aromatic thiols, internally etched silica encapsulated gold-coated silver (IE Ag@Au@SiO2) nanoparticles are used. First, localized surface plasmon resonance (LSPR) spectroscopy is implemented to estimate molecular tilt angle. Different tilt angles are then related to functional group induced surface density differences. Next, evaluation of SERS intensities and vibrational modes suggest that molecular tilt angle and surface selection rules govern the behavior observed in SERS intensities. Finally, concentration-dependent SERS signals are modeled using the Langmuir adsorption model. Equilibrium constants and free energies associated with adsorption are consistent with differences from London dispersion force...