Gold Film Electrode Research Articles

Electrochemical Impedance Immunosensor Based on Three-Dimensionally Ordered Macroporous Gold Film

A novel label-free immunosensor for the detection of C-reactive protein (CRP) was developed based on a three-dimensional ordered macroporous (3DOM) gold film modified electrode by using the electrochemical impedance spectroscopy (EIS) technique. The electrode was electrochemically fabricated with an inverted opal template, making the surface area of the 3DOM gold film up to 14.4 times higher than that of a classical bare flat one, characterized by the cyclic voltammetric (CV) technique. The 3DOM gold film which was composed of interconnected gold nanoparticles not only has a good biocompatible microenvironment but also promotes the increase of conductivity and stability. The CRP immunosensor was developed by covalently conjugating CRP antibodies with 3-mercaptopropionic acid (MPA) on the 3DOM gold film electrode. The CRP concentration was measured through the increase of impedance values in the corresponding specific binding of CRP antigen and CRP antibody. The increased electron-transfer resistance (R(et)) values were proportional to the logarithmic value of CRP concentrations in the range of 0.1 to 20 ng mL(-1). The detection of CRP levels in three sera obtained from hospital showed acceptable accuracy.

Deposition of Prussian blue on nanoporous gold film electrode and its electrocatalytic reduction of H2O2

Prussian blue-modified nanoporous gold film (PB-NPGF) electrode was fabricated in this study. The fabrication was realized through electrodeposition of Prussian blue nanoparticles on the skeleton of a nanoporous gold film electrode without destroying the porous structure of NPGF electrode. The resulting PB-NPGF composite electrode showed very high electrocatalytic activity, repeatability, and stability to the reduction of H2O2. For instance, its activity was about twenty times that of the PB-modified polished gold electrode. More importantly, the sensitivity of the PB-NPGF composite electrode reaches as high as 10.6 μA μM−1 cm−2. This PB-NPGF composite electrode is very promising in the fields of catalysis, analysis, and so on.

ChemInform Abstract: Direct Oxidation of Methanol on Self‐Supported Nanoporous Gold Film Electrodes with High Catalytic Activity and Stability.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A label-free DNA sensor based on impedance spectroscopy

This paper describes a label-free detection system for DNA strands based on gold electrodes and impedance measurements. A single-stranded 18 mer oligonucleotide (ssDNA) was immobilised via a thiol linker on gold film electrodes and served as probe DNA. Residual binding places were filled with mercaptobutanol. The sensor surface clearly distinguished between complementary and non-complementary target ssDNA. Additionally, detection of single base pair mismatches was possible. The electrode was impedimetrically characterised in the presence of the redox system ferri/ferrocyanide before and after DNA hybridisation. Impedance analysis showed that the charge transfer resistance, R ct, was increasing after DNA duplex formation, whereas the capacitive properties remain rather unaltered. The relative change of R ct was used as sensor parameter. Concentrations in the nanomolar range have been detected by the system. The sensor was reusable because a denaturation protocol allowed effective double strand dissociation without changing the surface properties of the electrode substantially. The time for DNA detection have been reduced to about 15 min including regeneration. The sensor signal was amplified by about 20% after binding of a negatively charged molecule to the formed DNA duplex. The sensor was also capable of sensing longer target ssDNA strands as shown with 25 mer and 37 mer oligonucleotides.

Analysis of photo-induced hydration of a photochromic poly( N-isopropylacrylamide) – Spiropyran copolymer thin layer by quartz crystal microbalance

We investigated hydration and swelling behavior of a solid state photoresponsive copolymer in water by using a quartz crystal microbalance technique with dissipation measurement (QCM-D technique). On the gold film electrode of a quartz resonator, we deposited a thin layer of a pNSp–NIPAAm, which is a poly( N-isopropylacrylamide) (pNIPAAm) polymer partially modified with a photochromic chromophore, 6-nitrospiropyran (NSp). Using QCM-D measurements, we found that at a temperature of 19 °C both water adsorption and changes in the viscoelasticity of the solid pNSp–NIPAAm layer were induced when pNSp–NIPAAm was irradiated by 365 nm ultraviolet light, which triggers the photoisomerization of the NSp chromophore and makes the structure of the chromophore hydrophilic. At temperatures between 25 and 35 °C, this photo-induced hydration was not observed. These observations suggest that the photoisomerization of the NSp chromophores triggered the photo-induced hydration only when pNIPAAm component is sufficiently hydrophilic, at a temperature of 19 °C.

Determination of mercury in table salt samples by on-line medium exchange anodic stripping voltammetry

A new method for the determination of traces of total mercury by using a gold film electrode in salt samples was developed. Table salts are known to contain mercury at ultra-trace level as well as a high quantity of chloride ions that cause severe disturbance during the stripping step when gold is used as the electrode material in voltammetric measurements. The interference of high chloride content in the determination of mercury was eliminated by reducing its concentration down to 3 × 10 −3 mol L −1 level which is optimum for the determination by using on-line medium exchange procedure immediately after the deposition step. The deposition potential applied to the electrode was maintained at 0.2 V (vs. Ag/AgCl double junction electrode) while the cell content was sucked by a pump and replaced with fresh electrolyte simultaneously. The analyte loss resulted from the air contact of the electrode was prevented by this means. The mercury ions present in the salt samples were collected at +0.2 V for 60 s, the electrolyte was replaced by 0.1 mol L −1 HClO 4 and the potential was scanned, attaining a detection limit of 0.17 μg L −1, with R.S.D. of 1.2% (S/N = 3). The recovery of the method was 94.6%. The performance and accuracy of the method was compared with that of atomic fluorescence spectrometry (AFS). Consequently, this developed method can offer a wide range of application in saline samples.

Direct Oxidation of Methanol on Self-Supported Nanoporous Gold Film Electrodes with High Catalytic Activity and Stability

A novel self-supported nanoporous gold film electrode with ultrahigh surface area shows excellent electrocatalytic activity and stability toward the direct oxidation of methanol in alkaline solution. The activity of NPGF electrode was about 400 times that of the smooth gold electrode and did not decrease after 100 cycles of activity test.

Fabrication of Stable, Highly Flat Gold Film Electrodes with an Effective Thickness on the Order of 10 nm

Stable gold film electrodes were fabricated by a combination of sputtered gold and an epoxy adhesion layer on a glass substrate using the template-stripped technique. An XRR scan analysis indicated the thickness and roughness of the gold layer to be on the order of 10 nm and subnanometer, respectively. In spite of their small thickness, the electrode had sufficient conductivity and stuck to the subject during the electrochemical measurements as did the usual gold working electrodes.

Fabrication of Nanoporous Gold Film Electrodes with Ultrahigh Surface Area and Electrochemical Activity

Nanoporous gold film (NPGF) electrode was fabricated by applying multicyclic potential scans on a polished gold electrode in an electrolyte composed of ZnCl2 and benzyl alcohol. In the cathodic potential scan, Zn was first electrodeposited on the gold electrode surface, and Au−Zn alloy was then directly formed on the surface under an elevated temperature. In the subsequent anodic potential scan, dealloying of Zn took place, resulting in a nanostructured gold film. Furthermore, Zn was then electrodeposited onto the porous gold surface and a Au−Zn alloy was formed at the same time. Through controlling the parameters of cyclic voltammetry and cyclic times, we finally obtained a three-dimensional NPGF with nanopores. The resulting NPGF possessed ultrahigh roughness factor and surface area. Results showed that the electrochemical activity of the NPGF electrode was much higher than that of the polished gold electrode. We believe that the resulting NPGF electrode is promising in the fields of catalysis, sensors,...

A stripping chronopotentiometric (SCP) method with a gold film electrode for determining inorganic arsenic species in seawater

An electrochemical method based on stripping chronopotentiometry (SCP) with a gold film electrode has been developed for determining arsenic in seawater. The detection limits were 0.053 ppb (0.71 nM) and 0.022 ppb (0.29 nM) for total inorganic As (As(T)) and As(III) after deposition times of 60 and 150 s, respectively. Compared to other stripping chronopotentiometric methods that use a gold macroelectrode to perform measurements of arsenic in seawater, the procedure described here exhibits better sensitivity and a fourfold shorter deposition time. Among the SCP methods, our procedure had proven its ability to analyse arsenic(III) in seawater. It therefore allows the concentrations of the various arsenic inorganic species in seawater--i.e. As(T), As(III) and As(V)--to be analysed. The proposed method is reliable, inexpensive and compact. It was successfully applied to the study of arsenic speciation along the salinity gradient of the Penzé estuary (NW France).

Ultrasound-assisted treatment of coconut water samples for potentiometric stripping determination of zinc

This work describes the application of potentiometric stripping analysis (PSA) at mercury film electrodes for zinc determination in coconut water. A sample ultrasound-assisted treatment was developed and optimised for the total zinc determination by PSA. One milliliter of sample was treated with 2 mL of 1:1 (v/v) concentrated HCl and H2O2 (30% m/v) mixture in closed (4 mL) vessels under sonication (in ultrasonic bath), followed by a thermal step (in a boiling bath, for 15 min). This methodology was optimised for total zinc determination and was validated by graphite furnace atomic absorption spectrometry (GFAAS) analysis utilizing the sample without any treatment. The limit of detection obtained by the proposed PSA method was 1.35 µg L-1 (applying 45 s of preconcentration). Attempts to evaluate the amount of copper in the same sample show that the content of this metal is lower than the detection limits of both techniques, GFAAS and PSA (0.030 µg L-1 after 600 s of preconcentration) at gold film electrodes.

The impact of glia-derived extracellular matrices on the barrier function of cerebral endothelial cells: An in vitro study

The blood–brain barrier (BBB) is composed of the cerebral microvascular endothelium, which, together with astrocytes, pericytes, and the extracellular matrix (ECM), contributes to a “neurovascular unit”. It was our objective to clarify the impact of endogenous extracellular matrices on the barrier function of BBB microvascular endothelial cells cultured in vitro. The study was performed in two consecutive steps: (i) The ECM-donating cells (astrocytes, pericytes, endothelial cells) were grown to confluence and then removed from the growth substrate by a protocol that leaves the ECM behind. (ii) Suspensions of cerebral endothelial cells were seeded on the endogenous matrices and barrier formation was followed with time. In order to quantify the tightness of the cell junctions, all experiments were performed on planar gold-film electrodes that can be used to read the electrical resistance of the cell layers as a direct measure for endothelial barrier function (electric cell–substrate impedance sensing, ECIS). We observed that endogenously isolated ECM from both, astrocytes and pericytes, improved the tightness of cerebral endothelial cells significantly compared to ECM that was derived from the endothelial cells themselves as a control. Moreover, when cerebral endothelial cells were grown on extracellular matrices produced by non-brain endothelial cells (aorta), the electrical resistances were markedly reduced. Our observations indicate that glia-derived ECM – as an essential part of the BBB – is required to ensure proper barrier formation of cerebral endothelial cells.

On-Site Determination of Arsenic in Soil Extract by Anodic Stripping Voltammetry with Gold Film Electrode after Solid Phase Pretreatment

A method for the on-site estimation of arsenic (As) contamination in soil by solid-phase extraction with a resin based on molecular recognition technology (SPE-MRT) and anodic stripping voltammetry (ASV) using a gold film microelectrode was developed. Optimized pretreatments were carried out as follows: 1 g of soil sample was taken and put into polypropylene test tube containing 33 mL 1 M hydrochloric acid solution, which was heated at 70 degree Celsius for 5 min using graphite block hot plate. As in the sample was extracted by shaking for 1 min using an automatic mini-shaker system. The extract was finally filtered through a 0.45 μm disk PTFE membrane filter. The extracted arsenic was electrodeposited on the gold film carbon microelectrode at −400 mV vs. Ag/AgCl for 1 min and the deposits were stripped at a rate of 5 mV/s to 580 mV vs. Ag/AgCl by using AnaLig® TE-3, Cu in soil extract was removed with 1 M hydrochloric acid for the determination of As. The method can eliminate Cu interference. The detection limit was 0.5 μg/L in soil extract. The results of voltammograms for As in the extracts from real soil samples were the same level as these obtained by a cross-check method using inductively coupled plasma mass spectroscopy (ICP-MS).

Substrate‐induced eosinophil adhesion requires intracellular Ca 2+ mobilization and PI‐3 kinase activation.

Human eosinophils spontaneously adhere to various substrates in the absence of exogenously added signaling molecules. Adhesion initially involves formation of a tethered attachment, followed by a rapid increase in intracellular Ca2+. In the present study we developed a method for characterizing adhesion in real time by measuring changes in impedance as eosinophils adhere to the surface of gold-film electrodes placed on the surface of a tissue culture dish. Impedance measurements were made in serum-free, HCO3 buffered HybriCare or DMEM media maintained in a humidified 5% CO2 incubator at 37 °C. Impedance increased by more than 1 k within minutes after eosinophils (5 x 105 cells/well) made contact with the electrode and reached a peak within approximately 15 minutes. Blocking the increase in intracellular Ca2+ that precedes adhesion with BAPTA-AM (10 μM) completely inhibited the increase in impedance along with changes in cell shape typically observed in adherent cells. Moreover, pretreatment with anti-CD18 antibody to block substrate interactions with β2 integrins or jasplakinolide (2 μM), to induce actin polymerization, also abolished the increase in impedance and adherent morphology of the cells. Pretreatment of eosinophils with the PI-3 kinase inhibitors Wortmannin (5 μM) or LY294002 (5 μM) significantly reduced the increase in impedance, but only a relatively small decrease in impedance was detected when cells were treated with the pan-specific PKC inhibitor GF-109203X (2 μM). These results demonstrate a novel method for measuring eosinophil adhesion and show that Ca2+ mobilization and PI-3 kinase activation are essential for substrate-induced adhesion to occur.

Electroanalysis of Crude Oil and Petroleum-Based Fuel for Trace Metals: Evaluation of Different Microwave-Assisted Sample Decompositions and Stripping Techniques

Electroanalytical stripping techniques have been well-used for trace-metal determinations, because of their remarkable sensitivity and selectivity. However, when these techniques are applied for organic materials, such as crude oil and petroleum-based fuels, the samples must be decomposed. This paper evaluates the use of different microwave ovens for the decomposition of crude oil and diesel fuel to determine the content of copper, lead, mercury, and zinc in the digestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2, operated at atmospheric pressure, and a closed-vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Square-wave stripping voltammetry (SWSV) and stripping chronopotentiometry (SCP) at gold film electrodes were applied for copper, lead, and mercury. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for copper, lead, and zinc. SWSV was more affected by residual organic matter, especially for lead determination. SCP presented higher sensitivity for copper and mercury at gold electrodes. PSA at mercury electrodes was preferred for lead and zinc determination. Better detection limits were attained for FM-digested solutions, after 0.8−1.0 g of sample can be digested, in contrast to the low quantities (0.10−0.25 g) used when pressurized vessels were explored. Nevertheless, the loss of mercury was verified when samples were decomposed in the FM oven.

Voltammetric detection of single base-pair mismatches and quantification of label-free target ssDNA using a competitive binding assay

The application of electrochemical techniques for DNA detection is motivated by their potential to detect hybridisation events in a more rapid, simplistic and cost-effective manner compared to conventional optical assays. Here, we present an electrochemical DNA sensor for the specific and quantitative detection of single-stranded DNA (ssDNA). Probe oligonucleotides were immobilised onto thin gold film electrodes by a 5′-thiol-linker. Hybridisation was detected by means of the electroactive redox-marker methylene blue (MB) covalently attached to the 5′-end of the target ssDNA and voltammetric techniques. MB-labeled target ssDNA was recognised down to 30 pmol. By application of a competitive binding assay, non-labeled ssDNA was detected down to 3 pmol. In addition, the DNA-modified electrodes were capable of sensing single base-pair mismatches at different positions within the sequence of the hybridised double-stranded DNA (dsDNA).

A Microfluidic Channel Flow Cell for Electrochemical ESR

The design, fabrication, and characterization of microfluidic channel flow devices for in situ simultaneous hydrodynamic electrochemical ESR is reported. The microelectrochemical reactors consist of gold film electrodes situated within rectangular ducts of height 350 microm and widths in the range 500-2000 microm. The small dimensions of the channels result in minimal dielectric loss when centralized within a cylindrical TE011 resonant cavity, leading to a high level of sensitivity. This is demonstrated by using the one-electron oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in acetonitrile as a model system, wherein the ESR spectra obtained for the corresponding stable radical cation are of a high signal-to-noise ratio. Signal intensity is measured as a function of flow rate for this system, and the behavior is validated by means of 3-dimensional numerical modeling of the hydrodynamic flow profile.

Electrocatalytic activity of silver modified gold film for glucose oxidation and its potential application to fuel cells

The electrocatalytic activity of the submonolayer silver modified gold film electrodes for the glucose oxidation in alkaline solution and the influences of the electrode size, the glucose concentration and the supporting electrolyte concentration on the reaction were investigated using cyclic voltammetry. The performance of a fuel cell utilizing the glucose oxidation was also evaluated. Gold film electrodes of large size were prepared by evaporating gold onto micas. The submonolayer modification of gold electrodes by silver underpotential deposition resulted in about 0.1 V negative shift in peak potential and a little larger current in the glucose oxidation, and the peak current obtained was proportional to the electrode size and the glucose concentration. The oxidation peak was also affected by the supporting electrolyte, showing a positive shift in potential and a drop in current if a certain concentration of sodium hydroxide was not reached. The catalytic activity of the silver modified gold film electrodes was stable, and a certain power of electricity was obtained with a glucose–air fuel cell.

Dual Roles of Tight Junction-associated Protein, Zonula Occludens-1, in Sphingosine 1-Phosphate-mediated Endothelial Chemotaxis and Barrier Integrity

In this report, sphingosine-1-phosphate (S1P), a serum-borne bioactive lipid, is shown to activate tight-junction-associated protein Zonula Occludens-1 (ZO-1), which in turn plays a critical role in regulating endothelial chemotaxis and barrier integrity. After S1P stimulation, ZO-1 was redistributed to the lamellipodia and cell-cell junctions via the S1P1/G(i)/Akt/Rac pathway. Similarly, both endothelial barrier integrity and cell motility were significantly enhanced in S1P-treated cells through the G(i)/Akt/Rac pathway. Importantly, S1P-enhanced barrier integrity and cell migration were abrogated in ZO-1 knockdown cells, indicating ZO-1 is functionally indispensable for these processes. To investigate the underlying mechanisms, we demonstrated that cortactin plays a critical role in S1P-induced ZO-1 redistribution to the lamellipodia. In addition, S1P significantly induced the formation of endothelial tight junctions. ZO-1 and alpha-catenin polypeptides were colocalized in S1P-induced junctional structures; whereas, cortactin was not observed in these regions. Together, these results suggest that S1P induces the formation of two distinct ZO-1 complexes to regulate two different endothelial functions: ZO-1/cortactin complexes to regulate chemotactic response and ZO-1/alpha-catenin complexes to regulate endothelial barrier integrity. The concerted operation of these two ZO-1 complexes may coordinate two important S1P-mediated functions, i.e. migration and barrier integrity, in vascular endothelial cells.

Stability of the Gold/Silica Thin Film Interface: Electrochemical and Surface Plasmon Resonance Studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.