Nanoporous Gold Electrode Research Articles

Spiral nanoporous gold electrode: A simple strategy for enhancing the attenuated-total-reflection infrared spectroelectrochemical sensitivity

• A new designed ATR-IR-SEC cell was used for spectroelectrochemical analysis. • A conventional three-electrode cell was used. • A spiral nanoporous gold electrode was used to enhance the sensitivity. • Ferricyanide and two antioxidants were determined using this new cell. In this study, a conventional three-electrode cell was used for the attenuated-total-reflection infrared spectroelectrochemical (ATR-IR-SEC) detection but an innovative spiral nanoporous gold electrode (SNPGE), which was prepared by a one-pot single-step method, was employed as the working electrode to enhance the spectroelectrochemical sensitivity. Potassium ferricyanide (K 3 Fe(CN) 6 ) was used as a model compound for evaluating the performance of the ATR-IR-SEC cell and two antioxidants, gallic acid and n -propyl gallate, were determined using this device to know the potential applicability.

Non-enzymatic hydrogen peroxide sensor based on a nanoporous gold electrode modified with platinum nanoparticles

AbstractA novel non-enzymatic electrochemical sensor based on a nanoporous gold electrode modified with platinum nanoparticles was constructed for the determination of hydrogen peroxide (H2O2). Platinum nanoparticles exhibit good electrocatalytic activity towards hydrogen peroxide. The nanoporous gold (NPG) increases the effective surface area and has the capacity to promote electron-transfer reactions. With electrodeposition of Pt nanoparticles (NPs) on the surface of the nanoporous gold, the modified Au electrode afforded a fast, sensitive and selective electrochemical method for the determination of H2O2. The linear range for the detection of H2O2 was from 1.0 × 10−7 M to 2.0 × 10−5 M while the calculated limit of detection was 7.2 × 10−8 M on the basis of the 3σ/slope (σ represents the standard deviation of the blank samples). These findings could lead to the widespread use of electrochemical sensors to detect H2O2.

Aptamer-based electrochemical biosensor for detection of adenosine triphosphate using a nanoporous gold platform

In spite of the promising applications of aptamers in the bioassays, the development of aptamer-based electrochemical biosensors with the improved limit of detection has remained a great challenge. A strategy for the amplification of signal, based on application of nanostructures as platforms for the construction of an electrochemical adenosine triphosphate (ATP) aptasensor, is introduced in the present manuscript. A sandwich assay is designed by immobilizing a fragment of aptamer on a nanoporous gold electrode (NPGE) and its association to second fragment in the presence of ATP. Consequently, 3, 4-diaminobenzoic acid (DABA), as a molecular reporter, is covalently attached to the amine-label of the second fragment, and the direct oxidation signal of DABA is followed as the analytical signal. The sensor can detect the concentrations of ATP as low as submicromolar scales. Furthermore, 3.2% decrease in signal is observed by keeping the aptasensor at 4°C for a week in buffer solution, implying a desirable stability. Moreover, analog nucleotides, including GTP, UTP and CTP, do not show serious interferences and this sensor easily detects its target in deproteinized human blood plasma.

Synthesis of Nanoporous Gold Electrode and Its Application in Electrochemical Sensor

Abstract In ammonia solution, binary gold-silver alloy films were directly deposited onto indium tin oxide (ITO) substrate surface by using electrochemical method with chloroauric acid and silver nitrate as precursors. Then high-surface-area nanoporous gold (NPG) film modified electrodes were fabricated by chemical dealloying of the less noble component silver from the surface. The modified electrodes were characterized. The electrode prepared can be successfully functionalized with self-assembled monolayers of L-cysteine, which can be applied to the sensitive and selective determination of Cu(II). Under the optimal conditions and 5 min of absorption time for Cu(II) ions, the cathodic current is linearly proportional to Cu(II) concentration ranged from 0.05 to 4 μM with a detection limit of 0.03 μM. The relative standard deviation is 4.3% for 1 μM Cu(II) solution. The established method was successfully applied for the determination of Cu(II) in water samples of environment.

Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry

Nanoporous gold prepared by dealloying Au:Ag alloys has recently become an attractive material in the field of analytical chemistry. This conductive material has an open, 3D porous framework consisting of nanosized pores and ligaments with surface areas that are 10s to 100s of times larger than planar gold of an equivalent geometric area. The high surface area coupled with an open pore network makes nanoporous gold an ideal support for the development of chemical sensors. Important attributes include conductivity, high surface area, ease of preparation and modification, tunable pore size, and a bicontinuous open pore network. In this paper, the fabrication, characterization, and applications of nanoporous gold in chemical sensing are reviewed specifically as they relate to the development of immunosensors, enzyme-based biosensors, DNA sensors, Raman sensors, and small molecule sensors.

Ultrasensitive electrochemiluminescence immunosensor based on nanoporous gold electrode and Ru-AuNPs/graphene as signal labels

In the paper, a simple and sensitive sandwich-type electrochemiluminescence (ECL) immunosensor was proposed for the detection of cancer antigen 125 (CA 125) on a nanoporous gold (NPG) modified glassy carbon electrode (GCE). The NPG was easily prepared by a selective dissolution of silver from silver/gold alloy in nitric acid. The fabrication of Ru(bpy)32+-gold nanoparticles (Ru-AuNPs) aggregates was owing to the electrostatic interactions between citrate-capped AuNPs and Ru in aqueous medium. The Ru-AuNPs composite assembled with poly(diallyldimethylammonium chloride) functionalized graphene nanosheets (GR) (Ru-AuNPs/GR) was used as ECL labels, which has large surface area, good biocompatibility and electronic conductivity. The ECL intensity observed by the application of as-prepared Ru-AuNPs/GR composites was enhanced 6-fold compared to those of Ru-AuNPs. The primary antibody of CA 125 (Ab1) was first immobilized on the NPG modified electrode, then the antigen and the secondary antibody (Ab2) were conjugated to form a sandwich-type immunocomplex through the specific interaction. The proposed ECL immunosensor provided a wide linear response range over 0.01–100UmL−1 with a detection limit of 0.005UmL−1. The ECL immunosensor showed high sensitivity, good reproducibility, satisfied regeneration and selectivity, and may exhibit an attractive approach for other analyte determination.

Effects of adsorption and confinement on nanoporous electrochemistry

Characteristic molecular dynamics of reactant molecules confined in the space of the nanometer scale augments the frequency of collisions with the electrified surface so that a given faradaic reaction can be enhanced at nanoporous electrodes, the so-called nano-confinement effect. Since this effect is grounded on diffusion inside nanopores, it is predicted that adsorption onto the surface will seriously affect the enhancement by nano-confinement. We experimentally explored the correlation between adsorption and the confinement effect by examining the oxidation of butanol isomers at platinum and gold nanoporous electrodes. The results showed that electrooxidation of 2-butanol, which is a non-adsorption reaction, was enhanced more than that of 1-butanol, which is an adsorption reaction, at nanoporous platinum in acidic media. In contrast, the nanoporous gold electrode, on which 1-butanol is less adsorptive than it is on platinum, enhanced the electrooxidation of 1-butanol greatly. Furthermore, the electrocatalytic activity of nanoporous gold for oxygen reduction reaction was improved so much as to be comparable with that of flat Pt. These findings show that the nano-confinement effect can be appreciable for electrocatalytic oxygen reduction as well as alcohol oxidation unless the adsorption is extensive, and suggests a new strategy in terms of material design for innovative non-noble metal electrocatalysts.

Anodization strategy to fabricate nanoporous gold for high-sensitivity detection of p-nitrophenol

The anodization of a gold electrode in oxalic acid aqueous solution of different concentration has been investigated at different applied potentials, which enables the formation of nanoporous gold (NPG). Electrochemical measurements show that the electrochemically active surface areas of the as-anodized Au samples show an obvious potential, electrolyte concentration and time dependence. The as-prepared NPG samples were used as the working electrode to investigate the redox behavior of p-nitrophenol (p-NP) by cyclic voltammetry (CV). The CV profiles of NPG display a pair of redox peaks, and the peak current densities increase linearly with increasing p-NP concentration. Besides, o-nitrophenol (o-NP) has little influence on the electrochemical detection of p-NP. Through the anodization strategy, NPG electrodes with a high sensitivity and good selectivity can be developed to detect trace p-NP in water.

Synthesis of Nanoporous Gold Electrode and Its Application in Electrochemical Sensor

In ammonia solution,binary gold-silver alloy films were directly deposited onto indium tin oxide(ITO) substrate surfaces using electrochemical method from chloroauric acid and silver nitrate.Then high-surface-area nanoporous gold(NPG) film modified electrodes were fabricated by chemical dealloying of the less noble component silver from the surface.The modified electrodes were characterized.The electrode can be successfully functionalized with self-assembled monolayers of L-cysteine,which can be applied to the sensitive and selective determination of Cu2+.Under the optimal conditions and 5 min of absorption time for Cu2+ ions,the cathodic current was linear proportional with Cu2+ concentration from 0.05 to 4 μmol/L with a detection limit of 0.03 μmol/L.The relative standard deviation was 4.3% for 1 μmol/L Cu2+ solution.The established method was successfully applied for the determination of Cu2+ in water sample of environment.

Mediated electron transfer of cellobiose dehydrogenase and glucose oxidase at osmium polymer-modified nanoporous gold electrodes

Nanoporous and planar gold electrodes were utilised as supports for the redox enzymes Aspergillus niger glucose oxidase (GOx) and Corynascus thermophilus cellobiose dehydrogenase (CtCDH). Electrodes modified with hydrogels containing enzyme, Os-redox polymers and the cross-linking agent poly(ethylene glycol)diglycidyl ether were used as biosensors for the determination of glucose and lactose. Limits of detection of 6.0 (±0.4), 16.0 (±0.1) and 2.0 (±0.1) μM were obtained for CtCDH-modified lactose and glucose biosensors and GOx-modified glucose biosensors, respectively, at nanoporous gold electrodes. Biofuel cells composed of GOx- and CtCDH-modified gold electrodes were utilised as anodes, together with Myrothecium verrucaria bilirubin oxidase (MvBOD) or Melanocarpus albomyces laccase as cathodes, in biofuel cells. A maximum power density of 41 μW/cm(2) was obtained for a CtCDH/MvBOD biofuel cell in 5 mM lactose and O2-saturated buffer (pH 7.4, 0.1 M phosphate, 150 mM NaCl).

Direct electron transfer of Trametes hirsuta laccase adsorbed at unmodified nanoporous gold electrodes

The enzyme Trametes hirsuta laccase undergoes direct electron transfer at unmodified nanoporous gold electrodes, displaying a current density of 28μA/cm2. The response indicates that ThLc was immobilised at the surface of the nanopores in a manner which promoted direct electron transfer, in contrast to the absence of a response at unmodified polycrystalline gold electrodes. The bioelectrocatalytic activity of ThLc modified nanoporous gold electrodes was strongly dependent on the presence of halide ions. Fluoride completely inhibited the enzymatic response, whereas in the presence of 150mM Cl−, the current was reduced to 50% of the response in the absence of Cl−. The current increased by 40% when the temperature was increased from 20°C to 37°C. The response is limited by enzymatic and/or enzyme electrode kinetics and is 30% of that observed for ThLc co-immobilised with an osmium redox polymer.

Electrochemical characterization of globotriose-containing self-assembled monolayers on nanoporous gold and their binding of soybean agglutinin

Self-assembled monolayers (SAMs) of α-d-Gal-(1→4)-β-d-Gal-(1→4)-β-d-Glc-mercaptooctane (globotriose, Gb3-C8-SH) were prepared both as single-component SAMs and as mixed SAMs with either octanethiol (OCT) or 8-mercapto-3,6-dioxaoctanol (HO-PEG2-SH), on flat gold and on nanoporous gold (NPG) electrodes. The binding of soybean agglutinin (SBA) to the globotriose (Gb3) unit in the SAMs was then studied using electrochemical impedance spectroscopy (EIS), which is a label free method found to be quite sensitive to SAM composition and to the differences in SAM structure on NPG versus on flat Au. The affinity of SBA to the mixed SAM of HO-PEG2-SH and Gb3-C8-SH on NPG is found to be greater on NPG than on flat gold, and indicates a potential advantage for NPG as a substrate. The SAMs of HO-PEG2-SH were found to resist protein adsorption on either NPG or flat gold. The non-specific adsorption of SBA to OCT SAMs on flat Au was observed in EIS by the increase in charge transfer resistance; whereas, the increase seen on the NPG surface was smaller, and suggests that EIS measurements on NPG are less affected by non-specific protein adsorption. Atomic force microscopy (AFM) images of the SBA binding to mixed SAM of HO-PEG2-SH and Gb3-C8-SH on NPG showed a greater number of proteins on top of the OCT containing SAMs.

Nanoporous gold electrode as a platform for the construction of an electrochemical DNA hybridization biosensor

The application of a nanoporous gold electrode (NPGE) in the fabrication of an electrochemical sensing system for the detection of single base mismatches (SBMs) using ferrocene-modified DNA probe has been investigated in the present manuscript. Ferrocene carboxylic acid is covalently attached to the amino-modified probe using EDC/NHS chemistry. By covalent attachment of the redox reporter molecules on the top of DNA, the direct oxidation of the ferrocene on the electrode surface is avoided. On the other hand, the electrochemical signals are amplified by anodizing the electrode surface and converting it to nanoporous form. By improving the sensitivity of the biosensor, the different SBMs including the thermodynamically stable G–A and G–T mismatches, can be easily distinguished. In this research, NPGE was prepared by anodization and chemical reduction of Au surface and used for signal amplification. Nanoporous electrode enhances the sensitivity of DNA biosensor and makes it capable to detect complementary target DNA in sub-nanomole scales.

Inkjet Printing of Nanoporous Gold Electrode Arrays on Cellulose Membranes for High-Sensitive Paper-Like Electrochemical Oxygen Sensors Using Ionic Liquid Electrolytes

A simple approach to the mass production of nanoporous gold electrode arrays on cellulose membranes for electrochemical sensing of oxygen using ionic liquid (IL) electrolytes was established. The approach, combining the inkjet printing of gold nanoparticle (GNP) patterns with the self-catalytic growth of these patterns into conducting layers, can fabricate hundreds of self-designed gold arrays on cellulose membranes within several hours using an inexpensive inkjet printer. The resulting paper-based gold electrode arrays (PGEAs) had several unique properties as thin-film sensor platforms, including good conductivity, excellent flexibility, high integration, and low cost. The porous nature of PGEAs also allowed the addition of electrolytes from the back cellulose membrane side and controllably produced large three-phase electrolyte/electrode/gas interfaces at the front electrode side. A novel paper-based solid-state electrochemical oxygen (O(2)) sensor was therefore developed using an IL electrolyte, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). The sensor looked like a piece of paper but possessed high sensitivity for O(2) in a linear range from 0.054 to 0.177 v/v %, along with a low detection limit of 0.0075% and a short response time of less than 10 s, foreseeing its promising applications in developing cost-effective and environment-friendly paper-based electrochemical gas sensors.

Highly sensitive and selective electrochemical detection of L-cysteine using nanoporous gold

Nanoporous gold (NPG) with uniform pore sizes and ligaments was prepared by using a simple dealloying method. NPG electrodes exhibit excellent electrocatalytic activity towards the oxidation of CySH and the mechanism for the electrochemical reaction of CySH on NPG has been discussed. Interestingly, if the operating potential is fixed at 0.65 V, a strong current is observed and interferences by tryptophan and tyrosine are avoided. The calibration plot is linear in the concentration range from 1 μM to 400 μM (R2 = 0.994), and the quantification limit is as low as 50 nM. The NPG-modified electrode has good reproducibility, high sensitivity and selectivity, can be used to sense CySH in aqueous solution.

Ultrasensitive electrochemiluminescence detection of DNA based on nanoporous gold electrode and PdCu@carbon nanocrystal composites as labels

A sensitive electrochemiluminescence (ECL) DNA biosensor based on nanoporous gold (NPG) electrode and PdCu@carbon nanocrystals (CNCs) composites is developed. The CNCs were obtained simply by electrooxidation with abundant carboxyl groups at their surfaces. The NPG can be easily prepared by a selective dissolution of silver from silver-gold alloy in nitric acid, which has free-standing noble metal membranes with controllable three-dimensional (3D) porosity. The PdCu bimetallic nanocomposites with hierarchically hollow structures were fabricated through a simple replacement reaction using dealloyed nanoporous copper (NPC) as both a template and reducing agent. Structure characterization was obtained by means of transmission electron microscope (TEM) and scanning electron microscope (SEM) images. The PdCu@CNCs composites exhibit 6 times higher ECL intensity than the pure CNC-labeled reporter DNA. Taking advantage of dual-amplification effects of the developed probe, a limit of detection as low as 18 aM can be achieved and the assay exhibits excellent selectivity for single-mismatched DNA detection even in human serum. The proposed ECL based method should have wide applications in diagnosis of genetic diseases due to its simplicity, low cost, and high sensitivity at extremely low concentrations.

Direct electron transfer of bilirubin oxidase (Myrothecium verrucaria) at an unmodified nanoporous gold biocathode

Well defined mediatorless bioelectrocatalytic reduction of oxygen with high current densities of 0.8mAcm−2 was obtained on nanoporous gold electrodes modified with Myrothecium verrucaria bilirubin oxidase. A stable faradaic response was observed when the enzyme modified electrode was coated with a specifically designed electrodeposition polymer layer. The response of the enzyme electrode was only slightly inhibited by the addition of F−.

Electrochemical detection of hydrazine using a highly sensitive nanoporous gold electrode

A facile alloy–dealloy technique performed in aqueous media was employed to prepare a nanoporous gold (NPG) electrode that demonstrated extremely high sensitivity toward hydrazine oxidation. An Ag ∼60Au ∼40 alloy was electrodeposited at a constant potential on sequentially Cr- and Au-deposited indium tin oxide (Au/Cr/ITO) from a bath that contained sulfuric acid, thiourea, HAuCl 4·3H 2O, and AgNO 3. The dealloying step was performed in concentrated HNO 3, where Ag in the alloy was selectively oxidized to leave the NPG structure. The NPG electrode was employed to study the hydrazine oxidation in basic phosphate buffer solution (PBS), and the results were compared with those obtained using the gold nanoparticle (AuNP)-modified ITO (AuNP/ITO) electrode. The NPG electrode demonstrated an unusual surface-confined behavior, which probably resulted from the thin-layer characteristics of the nano-pores. Hydrazine was detected by hydrodynamic chronoamperometry (HCA) at +0.2 V (vs. Ag/AgCl). The steady-state oxidative current exhibited a linear dependence on the hydrazine concentration in the concentration range of 5.00 nM–2.05 mM, and the detection limit was 4.37 nM ( σ = 3). This detection limit is the lower than the detection limits reported in the current literature concerning the electrochemical detection of hydrazine. The NPG electrode indeed demonstrates greater stability after hydrazine detection than the AuNP/ITO electrode.

A Sensitive Nanoporous Gold-Based Electrochemical DNA Biosensor for Escherichia coli Detection

A sensitive electrochemical DNA biosensor based on a mixed monolayer structure self-assembled at nanoporous gold (NPG) electrode surface was prepared for Escherichia coli (E. coli) detection. The NPG was fabricated on gold electrode, onto which thiolated oligonucleotides (SH-DNA) and mercaptohexanol (MCH) were covalently linked forming a mixed self-assembled monolayer (SAM). The hybridization between the SH-DNA/MCH modified biosensor and E. coli DNA was monitored with differential pulse voltammetry measurement using methylene blue (MB) as the hybridization indicator. The biosensor can detect 1 × 10−12 M DNA target and 50 cfu/μL E. coli without any nucleic acid amplification steps. The detection limit was lowered to 50 cfu/mL after 5.0 h of incubation.

Characterization of Nanoporous Gold Electrodes for Bioelectrochemical Applications

The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a gold-silver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A(real). Values of A(real) up to 28 times that of the geometric electrode surface area, A(geo), were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A(geo). The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A(macro), such as cyt c was reduced by up to 40% compared to A(real), demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm(-2) were obtained in unstirred solutions.