Etching Of Gold Research Articles

Colorimetric sensing of lead ion using gold nanorod with enhanced sensitivity via catalytic etching

AbstractLead, a prevalent heavy metal, poses significant risks to human health through various exposure pathways. Herein, we propose an extremely sensitive assay toward lead ion (Pb2+) using gold nanorods (GNRs) as probes based on its catalytic activity on etching gold in the presence of 2‐mercaptoethanol and sodium thiosulfate. In the presence of Pb2+, etching predominantly occurs at the two ends of GNRs, leading to the reduction of aspect ratio and the corresponding blueshift of the localized surface plasmon resonance (LSPR). With increasing Pb2+ concentration over the range of 0–50 μM, the color of GNR solution lightens, ultimately becoming colorless. The wavelength shift (Δλ) of LSPR is highly dependent on Pb2+ concentration, with a linear regression equation of Δλ = 10.05ln[Pb2+] + 9.59 and an R2 = 0.995. The assay demonstrates high selectivity for Pb2+ over other potentially interfering ions such as Cu2+ because of its special catalytic activity in the etching of GNRs and the complexing ability of 2‐mercaptoethanol and sodium thiosulfate. Validation of the assay was accomplished by analyzing several forest‐derived food samples, affirming the accuracy in real‐world scenarios. The assay we developed holds promise for many applications in environmental protection and food safety.

Gold Nanorod Growth and Etching Activated by Femtosecond Irradiation and Surface Plasmon Resonance

Gold Nanorod Growth and Etching Activated by Femtosecond Irradiation and Surface Plasmon Resonance

Alternative nano-lithographic tools for shell-isolated nanoparticle enhanced Raman spectroscopy substrates.

Chemically synthesized metal nanoparticles (MNPs) have been widely used as surface-enhanced Raman spectroscopy (SERS) substrates for monitoring catalytic reactions. In some applications, however, the SERS MNPs, besides being plasmonically active, can also be catalytically active and result in Raman signals from undesired side products. The MNPs are typically insulated with a thin (∼3 nm), in principle pin-hole-free shell to prevent this. This approach, which is known as shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), offers many advantages, such as better thermal and chemical stability of the plasmonic nanoparticle. However, having both a high enhancement factor and ensuring that the shell is pin-hole-free is challenging because there is a trade-off between the two when considering the shell thickness. So far in the literature, shell insulation has been successfully applied only to chemically synthesized MNPs. In this work, we alternatively study different combinations of chemical synthesis (bottom-up) and lithographic (top-down) routes to obtain shell-isolated plasmonic nanostructures that offer chemical sensing capabilities. The three approaches we study in this work include (1) chemically synthesized MNPs + chemical shell, (2) lithographic substrate + chemical shell, and (3) lithographic substrate + atomic layer deposition (ALD) shell. We find that ALD allows us to fabricate controllable and reproducible pin-hole-free shells. We showcase the ability to fabricate lithographic SHINER substrates which report an enhancement factor of 7.5 × 103 ± 17% for our gold nanodot substrates coated with a 2.8 nm aluminium oxide shell. Lastly, by introducing a gold etchant solution to our fabricated SHINER substrate, we verified that the shells fabricated with ALD are truly pin-hole-free.

Wet etching of gold on graphene for high-quality resist-free graphene surfaces

Wet etching of gold on graphene is challenging due to the weak adhesion of the resist mask to graphene. We report an operating procedure for alkali ion-free wet etching of gold on graphene using a mixture of hydrochloric and nitric acids (aqua regia) with a high lateral resolution down to 100 nm. We investigate the role of positive and negative resists, electron beam lithography (EBL) dose, hard-bake, oxygen etching, aging, and sensitivity to the etch parameters, such as the freshness of dilute aqua regia, etch time, and the order of etched samples. The negative-tone resist provides the best results. The over-dosed EBL exposure can enhance the resist adhesion, as hard-bake below the glass-transition temperature and well-defined wet etch of the resist-residua-free gold surface. We also present a cleaning procedure to avoid bubble formation after the hard bake. Our results demonstrate that wet etching of gold on graphene using aqua regia is a viable method for achieving high-quality resist-free graphene surfaces. This method has potential applications in graphene nanoelectronics and nanophotonics, where high-quality graphene surfaces are essential for device performance.

Long-Acting Real-Time Microscopic Monitoring Inside the Proton Exchange Membrane Water Electrolyzer

The proton exchange membrane water electrolyzer (PEMWE) requires a high operating voltage for hydrogen production to accelerate the decomposition of hydrogen molecules so that the PEMWE ages or fails. According to the prior findings of this R&D team, temperature and voltage can influence the performance or aging of PEMWE. As the PEMWE ages inside, the nonuniform flow distribution results in large temperature differences, current density drops, and runner plate corrosion. The mechanical stress and thermal stress resulting from pressure distribution nonuniformity will induce the local aging or failure of PEMWE. The authors of this study used gold etchant for etching, and acetone was used for the lift-off part. The wet etching method has the risk of over-etching, and the cost of the etching solution is also higher than that of acetone. Therefore, the authors of this experiment adopted a lift-off process. Using the flexible seven-in-one (voltage, current, temperature, humidity, flow, pressure, oxygen) microsensor developed by our team, after optimized design, fabrication, and reliability testing, it was embedded in PEMWE for 200 h. The results of our accelerated aging test prove that these physical factors affect the aging of PEMWE.

Multicolor Biosensor for Trypsin Detection Based on the Regulation of the Peroxidase Activity of Bovine Serum Albumin-Coated Gold Nanoclusters and Etching of Gold Nanobipyramids.

The detection of trypsin is significantly important for both clinical diagnosis and disease treatment. In this study, an innovative multicolor sensor for trypsin detection has been established based on the regulation of the peroxidase activity of bovine serum albumin-coated gold nanoclusters (BSA-Au NCs) and efficient etching of gold nanobipyramids (Au NBPs). BSA-Au NCs have slight peroxidase enzyme activity and can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate TMB+, while trypsin can hydrolyze BSA ligands on the surface of BSA-Au NCs, thus exposing more catalytic active sites of BSA-Au NCs and resulting in the enhancement of the peroxidase activity of BSA-Au NCs, hence more TMB+ is generated. Under acidic conditions, TMB+ can etch Au NBPs efficiently, consequently affecting the aspect ratio of Au NBPs accompanied by the ultraviolet-visible (UV-vis) spectra blue shifting of the system. Furthermore, this also results in color variations that can be distinguished and recognized by naked eyes without any expensive and sophisticated instruments. This multicolor sensor has an available linear relationship with the logarithm of the trypsin concentration in the range of 0.1-100 μg/mL, and the detection limit is 0.045 μg/mL. The designed sensor has been used to detect the concentration of trypsin in human serum samples from healthy individuals and pancreatitis patients with satisfactory results.

Multicolor immunosensor for detection of zearalenone based on etching Au NBPs mediated by HRP

Zearalenone (ZEN) is a low-weight molecule toxin which can cause great damage to human health. A multicolor immunosensor for determination of ZEN was developed based on etching gold nanobipyramids (Au NBPs) mediated by horseradish peroxidase (HRP). In this new immunosensor, the anti-ZEN monoclonal antibody (McAb) induced the formation of ternary immunocomplex BSA-ZEN@McAb@HRP-IgG. Then, TMB was converted to TMB+ under the catalysis of HRP. Subsequently, TMB+ reacted with H+ to form TMB2+. Finally, the Au NBPs was etched by TMB2+ to produce blue shift of longitudinal absorption peaks of Local Surface Plasmon Resonance (LSPR). Meanwhile, the solution exhibited different multiple colors, which can be recognized by the naked eyes. Under the optimal conditions, the limit of detection of this new immunosensor was 0.011 ng/mL, whose linear range was 0.02 ~ 0.80 ng/mL. Besides, this new immunosensor had good sensitivity for ZEN and potential application prospect.

Metallographic characterization of a gold-steel composite

Abstract A gold-steel composite material for decorative applications was manufactured by forging. This procedure can be referred to as modified damascene technique. Sheets made of steel K110 (C-rich cold work steel) and gold sheets were assembled and forged together at approx. 800 °C. The bar was subsequently twisted to obtain the typical torsion pattern. The end portions of this bar were subjected to a metallographic examination. The steel K110 shows broken carbides which were formed during the forging process. The carbides can be etched using Murakami’s reagent, whereas a 3 % Nital solution can be used to etch the steel matrix. Gold etching was challenging because many etchants suitable to etch gold preferentially attack the steel. In reference to gold extraction by cyanide leaching, a KCN solution was used as etchant. It could be shown that atmospheric oxygen acting as an oxidant is already sufficient to etch gold. However, using a KCN-H2O2 mixture provides a more efficient etching effect. Gold grains in the gold layers can reach a size of up to 1 mm. A diffusion zone with a thickness of approx. 10 μm can be observed at the steelgold interfaces.

A plasmonic ELISA for multi-colorimetric sensing of C-reactive protein by using shell dependent etching of Ag coated Au nanobipyramids

The etching of gold nanorods/nanobipyramid, or silver-coated nanorods/nanobipyramid inducing plasmon changes represents an efficient strategy to improve the performance of enzyme-linked immunosorbent assay (ELISA). However, the effect of shape on the sensitivity was negligible, especially the thickness of coated silver shell. Here, we propose a plasmonic ELISA for multi-colorimetric detection of CRP based on the etching of Ag-coated Au nanobipyramid (Au NBP@Ag). The effect of silver shell thickness on the sensitivity of plasmon peak shifting was investigated by experiments and DDA calculations. The relationship between the Ag shell thickness and the sensitivity of plasmon peak shifting was obtained. Our results reveal that the thickness of coated Ag shell acts as a key factor in the multi-color change of Au NBP@Ag etching. It is found that Au NBP@Ag with medium Ag shell thickness and rod-like shape has the higher sensitivity and is suitable for sensing. At the optimized most sensitive Ag shell, the detection limit of proposed plasmonic ELISA for CRP was determined to be 0.09 ng/mL with a spectrometer in the range from 0.09 ng/mL to 25 ng/mL. Importantly, the visual detection limit was 0.78 ng/mL, which allows the differential diagnosis with the naked eye. Compared with traditional ELISA with the monochromatic intensity variations, the multi-color ELISA proposed in this study has a large linear range and rich color variation for high-sensitivity and naked-eye semi-quantitative detection.

Appearance of an Electrochemical Oxidative Peak of Gold/Bis(trifluoromethylsulfonyl)amide-based Ionic Liquid Interfaces at Elevated Temperatures

Abstract The electrochemical behavior of a Au(111) electrode was investigated in three ionic liquids (ILs) containing trifluoromethylsulfonyl-based anions at temperatures ranging from 20 °C to 100 °C. Gold oxidation, that is, gold etching, occurred at elevated temperatures (≥70 °C) and was found to be dependent on the chemical structure of the ILs. These results allow us to simplify the procedure of gold dissolution in bis(trifluoromethylsulfonyl)amide-based ILs, thereby improving the efficiency of electrochemical etching.

Studies on Thiol Etching of Gold by Using QCM-D Sensor as the Sacrificial Probe.

There is still a lack of deep understanding on the reaction kinetics and mechanism of thiol etching of gold. Herein, by using the sensor of quartz crystal microbalance (QCM) as the sacrificial probe, the etching reaction of gold has been studied by employing cysteamine (CS) as a typical thiol etchant. The etching reaction is verified as diffusion-controlled and shows a half-order reaction kinetics. It is demonstrated that intact thiol and amino on CS are both crucial for its etching ability to gold. Applied potentials can affect the electron transfer and hence can be used to regulate the gold etching. Our results also reveal that only two carbon atoms of the spacer between thiol and amino on CS are very critical to the excellent etching ability. This work exhibits a new route to explore the thiol etching reaction of gold and elucidates the reaction kinetics and mechanism.

The Internal Structure of Placer Gold of the North-East of the Siberian Platform as a Reliable Search Sign of Primary Sources

Typomorphic features of placer gold are carriers of the most important information necessary for the reconstruction of the history of the formation of placer and ore occurrences of gold and can be used as mineralogical criteria in the search for primary sources of placers. The study of these features is relevant for placer areas with unidentified gold sources, which include the territory of the north-east of the Siberian Platform. The internal structure of native gold is one of the most informative typomorphic features is. We studied the internal gold structures of modern placers and conglomerates of the Early Permian age in the north-east of the Siberian Platform. The purpose of the work: to identify the features of the internal structure of placer gold, depending on the chemical composition and the degree of its transformations, as well as the possibility of their use as a prospecting indicator. Structural etching of native gold was performed using the reagent: HCl + HNO3 + FeCl3 × 6H2O + CrO3 + thiurea + water. As a result of the research, it was found that the well-rounded high-grade gold of modern placers has undergone repeated redeposition through intermediate sources. The discovery of slightly rounded gold with an internal structure without signs of exogenous transformation indicates that it entered the modern alluvium from a nearby primary source. This was a prerequisite for setting up ore gold exploration, resulting in identification of apocarbonate hydrothermal-metasomatic formations with disseminated gold-sulfide mineralization were identified. Thus, the features of the internal structures of placer gold in combination with other typomorphic features are additional indications of determining the sources of formation of gold-bearing placers.

Elucidating the Role of Halides and Iron during Radiolysis-Driven Oxidative Etching of Gold Nanocrystals Using Liquid Cell Transmission Electron Microscopy and Pulse Radiolysis.

Graphene liquid cell transmission electron microscopy (TEM) has enabled the observation of a variety of nanoscale transformations. Yet understanding the chemistry of the liquid cell solution and its impact on the observed transformations remains an important step toward translating insights from liquid cell TEM to benchtop chemistry. Gold nanocrystal etching can be used as a model system to probe the reactivity of the solution. FeCl3 has been widely used to promote gold oxidation in bulk and liquid cell TEM studies, but the roles of the halide and iron species have not been fully elucidated. In this work, we observed the etching trajectories of gold nanocrystals in different iron halide solutions. We observed an increase in gold nanocrystal etch rate going from Cl-- to Br-- to I--containing solutions. This is consistent with a mechanism in which the dominant role of halides is as complexation agents for oxidized gold species. Additionally, the mechanism through which FeCl3 induces etching in liquid cell TEM remains unclear. Ground-state bleaching of the Fe(III) absorption band observed through pulse radiolysis indicates that iron may react with Cl2·- radicals to form an oxidized transient species under irradiation. Complete active space self-consistent field (CASSCF) calculations indicate that the FeCl3 complex is oxidized to an Fe species with an OH radical ligand. Together our data indicate that an oxidized Fe species may be the active oxidant, while halides modulate the etch rate by tuning the reduction potential of gold nanocrystals.

Gold nanostar as an ultrasensitive colorimetric probe for picomolar detection of lead ion

The sensitivity for analytes of interest is vital for environment protection and food safety. Here, we propose an extremely sensitive assay toward Pb2+ by using gold nanostars (GNSs) as probes based on the catalytic activity of Pb on etching gold atoms after being reduced in the presence of 2-mercaptoethanol (2-ME) and sodium thiosulfate. GNSs were prepared by using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid as both the reducing and capping agents, enabling high stability and sensitivity for quantitation of Pb2+. Upon increasing Pb2+ concentration over the range of 0–10 μM, GNS solution color changed from greenish-blue to blue to purple to red, and eventually to colorless. The color change can be distinguished by naked eye at the Pb2+ concentration as low as 200 pM. Through monitoring longitudinal localized surface plasmon of GNSs, Pb2+ could be detected with a limit of detection of 1.5 pM, and the working range is 2 pM-1 μM. The ultra-high sensitivity of our assay stems from the high catalysis of Pb on etching gold on tips and branches in the presence of 2-ME and sodium thiosulfate, leading to the shape deformation to spherical gold nanoparticle and the corresponding significant changes in their optical properties. The assay provides high selectivity of Pb2+ over the tested interfering metal ions like Cu2+. With high sensitivity and selectivity, the assay was efficiently validated by analyzing water samples and monitoring the migration of Pb2+ from the tested container to water.

Challenges for impedimetric affinity sensors targeting protein detection

The review provides articles discussing big challenges behind successful design of impedimetric biosensors and the way such challenges were/could be addressed for highly sensitive affinity detection of proteins. In particular, the effect of gold etching by chloride ions or by CN − ions (released from the redox probe [Fe(CN) 6 ] 3-/4- ), the effect of ionic strength of the assay buffer; the effect of initial interfacial properties (capacitance) and the effect of the high analyte:bioreceptor ratio on electrochemical impedance spectroscopy–based biosensing are discussed. The review provides also short discussion related to other factors, which can significantly affect operational performance of electrochemical impedance spectroscopy–based biosensing including novel conductive interfaces, small bioreceptors, strategies for improved selectivity (nonbiofouling interfaces) and sensitivity (use of nanoparticles). • The review paper provides a short introduction to electrochemical impedance spectroscopy (EIS). • Three EIS modes of operation are discussed in the review paper. • Novel trends in EIS sensing are provided, as well.

Iodine adlayer mediated gold electrooxidation in bis(trifluoromethylsulfonyl)amide-based ionic liquids

Conventional complexing ligands for the wet etching of gold are hazardous, making large-scale utilization problematic. In particular, the environmental risks caused by these materials must be minimized. To address this problem, an electrochemical etching method for gold using bis(trifluoromethylsulfonyl)amide ([Tf2N]–)-based ionic liquids (ILs) has been developed. Here, only one layer of conventional complexing ligand, that is, iodine on gold, is required to achieve the continuous dissolution of gold under a positive electrode potential. In addition, the etching behavior involves sacrificial anode electrolysis (SAE) to generate gold nanoparticles (AuNPs). It was found that the electrochemical oxidation of gold is strongly dependent upon the type of halide ion, and the iodine-modified gold electrode produced a large oxidation peak in [Tf2N]–-based ILs. The voltammetric profiles of iodine-modified gold electrodes reveal that the electronic charge consumed during the electrochemical oxidation is affected by the IL cation and the crystallographic orientation of gold, increasing as ammonium < imidazolium < pyrrolidinium and Au(111) < Au(100) < Au(110), respectively. Of the IL anions evaluated in this study, the apparent oxidation peak was only observed for iodine-modified gold electrode in [Tf2N]–-based ILs, suggesting that [Tf2N]– anions promote gold complexation and act as ligands. Further, microscopic and spectroscopic measurements provide evidence of gold dissolution after electrochemical oxidation and the formation of gold complexes, followed by the generation of AuNPs. The results reveal a mechanism for the iodine-catalyzed electrochemical oxidation of gold in [Tf2N]–-based ILs. The electrolysis of gold in the ILs reported here opens avenues for acquiring novel aurate salts with IL anions and AuNPs.

Analysis of 8.71 GHz operated gold nanoparticles based multi-slotted patch antenna etched on epoxy dielectric material having broadsided radiation characteristics

This paper deals with the design and study of multi-slot patch antennas etched on a epoxy dielectric material coated with gold nanoparticles suitable for wireless system based applications. The antenna is uniformly coated with gold nanoparticles which tends have better conductivity compared to copper; the coating is done using sputtering process. In addition, the characteristics parameters of antenna etched on glass epoxy dielectric material are studied and they are return loss (RL), reflection co-efficient, 2D patterns, half power beamwdith (HPBW) and VSWR with conclusions are considered. The proposed antenna multi-slot epoxy substrate patch antenna1 (MSEPA 1) attained bandwidth (BW) of 2210 MHz (-37 dB of RL). A decent gain of 8.29 dB with VSWR less than 1.5 is obtained as the improving feature for the designed MSEPA1 through the experimental process. The dimensions of patch having length, width are kept constant as a factor of wavelength (λ). Desired antenna resonance with wide band characteristics is seen because of etching slots and gold nanoparticles deposition on dielectric material. Simulation is performed using electromagnetic simulation software MG IE3D V.15.3.

Plasmonic Colorimetric Biosensor for Sensitive Exosome Detection via Enzyme-Induced Etching of Gold Nanobipyramid@MnO2 Nanosheet Nanostructures

Exosomes involved in tumor-specific processes display excellent potential in the early diagnosis of cancer. Herein, a highly sensitive plasmonic colorimetric biosensor was proposed for exosome quantification. The sensing strategy mainly includes two steps: exosome-triggered competitive reaction and etching of gold nanobipyramid@MnO2 nanosheet nanostructures (Au NBP@MnO2 NSs). A competitive reaction between exosomes and placeholder chains induced by exosomes can translate the signal of exosomes into the amount of alkaline phosphatase, which simplifies the experimental process and amplifies the signal. The etching of Au NBP@MnO2 NSs by ascorbic acid generated from the hydrolysis of l-ascorbic acid 2-phosphate by alkaline phosphatase changes the refractive index of Au NBPs, accompanied by the blue shift of the longitudinal localized surface plasmon resonance peak. Profiting from the signal amplification of the competitive reaction and superior refractive index sensitivity of colorimetric substrates, this protocol exhibits high sensitivity toward exosomes within 8.5 × 102 to 8.5 × 104 particles μL-1, along with a detection limit of 1.35 × 102 particles μL-1, which is more sensitive than previously reported colorimetric methods. In addition, a sensitive multicolor visual detection of exosomes was realized by adjusting the aspect ratio of Au NBPs. It is worth mentioning that the Au NBP@MnO2 NSs was synthesized through in situ growth of MnO2 nanosheets on Au NBPs, and the attractive optical properties and ease of etching make Au NBP@MnO2 NSs promising candidates for plasmonic detection.

Additive-improved colorimetric nitrite assay with ultrahigh sensitivity based on etching gold nanorods

Gold nanomaterial (GNM)-based colorimetric sensors have gained particular attention in the analytical field because of their instrument-free, low-cost, and easy-to-use features. Herein, a universal strategy for improving the sensitivity of colorimetric assays, which is based on GNM etching, was proposed by using additives to shift the chemical equilibrium of the reactions. As a proof-of-concept demonstration, nitrite was detected with high sensitivity using gold nanorod (AuNR) by monitoring the shift of its longitudinal localized surface plasmonic resonance (Δλ) with the use of NH4Br and HCl. These two additives could change chemical equilibriums and promote the etching of more gold atoms at the AuNR ends. The assay is sensitive and 0.001 μM of nitrite could result in Δλ change by 3 nm. A linear relationship between Δλ and nitrite concentration was established (Δλ =22.8∗Cnitrite +9.7) in the range of 0.016–8.0 μM with a coefficient of 0.999. The reaction time was also accurately controlled by adjusting solution pH with NH3⋅H2O to terminate the test. The sensitivity of this colorimetric assay toward nitrite was significantly higher than that of the conventional Griess assay, while it was the highest among the reported GNM-based approaches. This method was successfully applied in determining the nitrite content in food samples, including waters, spinach, and rose petals, with less rigorous sample processing. The proposed strategy of using additives to alter chemical equilibriums to improve sensitivity could be extended to other GNM etching sensors.

Silver Double Nanorings with Circular Hot Zone.

Silver double nanorings with circular intra-nanogaps between two nanorings of different diameters were synthesized without a linker molecule to confine an incident electromagnetic field in a single entity. We used on-demand, rational, and systematic multi-stepwise reactions consisting of (1) selective etching of gold, (2) rim-on deposition of platinum, (3) eccentric growth of gold, and (4) concentric growth of silver. The resulting silver double nanorings exhibited a high degree of homogeneity in both shape and size, with strongly coupled circular hot zones (or "hot halos", referring to the circular intra-nanogaps capable of focusing the near electromagnetic field) resulting from strong surface plasmon coupling between the inner and outer nanorings. Remarkably, these silver double nanorings exhibited strong, stable, and reproducible single-particle surface-enhanced Raman scattering signals without blinking. The signals appeared independently of polarization directions, which is a unique feature of a circular hot halo. The estimated enhancement factor was between 2 × 108 and 7 × 108. The measured limit of detection was 10-7 M in bulk concentration, and the signal appeared 570 s after sample exposure.