Porous Gold Electrodes Research Articles

Highly Sensitive Membraneless Fructose Biosensor Based on Fructose Dehydrogenase Immobilized onto Aryl Thiol Modified Highly Porous Gold Electrode: Characterization and Application in Food Samples.

In this paper we present a new method to electrodeposit highly porous gold (h-PG) onto a polycrystalline solid gold electrode without any template. The electrodeposition is carried out by first cycling the electrode potential between +0.8 and 0 V in 10 mM HAuCl4 with 2.5 M NH4Cl and then applying a negative potential for the production of hydrogen bubbles at the electrode surface. After that the modified electrode was characterized in sulfuric acid to estimate the real surface area ( Areal) to be close to 24 cm2, which is roughly 300 times higher compared to the bare gold electrodes (0.08 cm2). The electrode was further incubated overnight with three different thiols (4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MPh), and 4-aminothiophenol (4-APh)) in order to produce differently charged self-assembled monolayers (SAMs) on the electrode surface. Finally a fructose dehydrogenase (FDH) solution was drop-cast onto the electrodes. All the modified electrodes were investigated by cyclic voltammetry both under nonturnover and turnover conditions. The FDH/4-MPh/h-PG exhibited two couples of redox peaks for the heme c1 and heme c2 of the cytochrome domain of FDH and as well as a well pronounced catalytic current density (about 1000 μA cm-2 in the presence of 10 mM fructose) due to the presence of -OH groups on the electrode surface, which stabilize and orientate the enzyme layer on the electrode surface. The FDH/4-MPh/h-PG based electrode showed the best analytical performance with an excellent stability (90% retained activity over 90 days), a detection limit of 0.3 μM fructose, a linear range between 0.05 and 5 mM, and a sensitivity of 175 ± 15 μA cm-2 mM-1. These properties were favorably compared with other fructose biosensors reported in the literature. The biosensor was successively tested to quantify the fructose content in food and beverage samples. No significant interference present in the sample matrixes was observed.

Nanostructured Porous Electrodes by the Anodization of Gold for an Application as Scaffolds in Direct-electron-transfer-type Bioelectrocatalysis.

In this study, nanostructured porous gold electrodes were prepared by the anodization of gold in the presence of oxalic acid or glucose as a reductant, and applied as scaffolds for direct electron transfer (DET)-type bioelectrocatalysis. Gold cations generated in the anodization seem to be reduced by the reductant to construct a porous gold structure. The DET-type performance of the electrode was examined using two DET-type model enzymes, bilirubin oxidase (BOD) and peroxidase (POD), for the four-electron reduction of dioxygen and the two-electron reduction of peroxide, respectively. BOD and POD on the anodized porous gold electrodes exhibited well-defined sigmoidal steady-state waves corresponding to DET-type bioelectrocatalysis. Scanning electron microscopy images revealed sponge-like pores on the electrodes. The anodized porous gold electrodes demonstrate promise as scaffolds for DET-type bioelectrocatalysis.

Electrochemical detection of arsenic(III) using porous gold via square wave voltammetry

Electrochemical detection of trace arsenic(III) in aqueous phase was studied with a porous gold (PAu) electrode, which was prepared by paper-based templating method. Square wave voltammetry was performed in As(III) solutions. The limit of detection of 0.1 ppb was obtained with a linear detection range of 0.1–14 ppb, which complies with the regulations for As(III) content in drinking water. The analysis of roughness factor and diffusion coefficient showed that the porous structure of the PAu electrode might have a stronger contribution to improving the sensitivity and selectivity of the target ion, compared to bulk gold electrode.

A Simple and Highly Stable Porous Gold‐based Electrochemical Sensor for Bisphenol A Detection

AbstractA porous gold electrode with a uniform pore size was prepared by a simple single potential step method. It provided around 19 times more surface area than a bare gold electrode. The porous gold electrode, without any modification, exhibited good electrocatalytic activity towards the oxidation of bisphenol A (BPA). The effect of the pH and scan rate, on the porous gold electrode was studied and discussed. Under optimum conditions of the flow system, the calibration plot of BPA was linear over a wide range of concentration, from 2.0 nM to 800 nM (R2=0.999), and the detection limit was 2.0 nM (s/n=3). It was of interest that, the porous gold electrode showed an exceptional result in minimizing the fouling from the oxidation product of BPA and led to a very high operational stability of the electrode for the detection of BPA (560 consecutive times). The porous gold electrode showed good fabrication reproducibility and can be used to detect bisphenol A that leached from baby bottles and drinking water bottles. The obtained results were in good agreement with the GC‐MS method (P>0.05).

Electrochemical degradation of organic dyes with a porous gold electrode

Electrochemical degradation of methylene blue (MB) and rhodamine B (RhB) was studied at porous gold (PAu) electrode in presence of KCl as supporting electrolytes. PAu electrode with three-dimensional porous structure was prepared by paper-based method and used as working electrode. Based on the cyclic voltammetric test, the redox potential of of MB and RhB contained in KCl solution was found and the electrochemical degradation was conducted at fixed applied voltage. The direct oxidation of organic dyes involved using PAu and Pt electrodes, while the indirect electrolysis was mediated by active chlorine electro-generated from KCl solution. The results showed that PAu electrode with porous structure has high electrochemical activity with fast kinetics for the destruction of RhB (0.0448 min-1) and low energy consumption (0.315 kWh/m3), compared to smooth Au foil and reported others. In addition, the durability test for 10 serial degradation showed that PAu electrode has a good reproducibility and high adaptability for practical application.

Sensing of bisphenol A and mercury ions in aqueous solutions using a functionalized porous gold electrode

Endocrine disrupting compounds (EDCs) such as bisphenol A (BPA) and mercury ions can accumulate in living tissue, causing many health problems. Therefore, to prevent contaminated water and products reaching consumers, it is necessary to develop a sensitive and efficient sensing system for these compounds. However, common analytical techniques for EDCs are based on mass spectrometry, which is both costly and requires an expert analyst. Herein, we describe the preparation of a functionalized, porous gold electrode for electrochemical sensing of BPA and mercury ions in aqueous solutions that is formed via a templating method and simple pressing. The prepared porous gold electrode was characterized by SEM-EDS, N2 adsorption-desorptions, and FTIR spectroscopy. The prepared porous gold has a very large surface area (8.1 m2/g) and comparable electrical conductivity (1.33 × 104 S/cm) to pure gold. To prevent electrode poisoning by oxidation byproducts of the target analytes, an indirect sensing method was used: the ferricyanide oxidation reaction. For hexyl and thiol-functionalized porous gold electrodes (C6–PAu and SH-PAu), a linear relationship between the current responses and the concentrations of BPA and mercury ions with high correlation coefficients (≥0.9998) at very low aqueous concentrations (≤0.7 μM) was found using differential pulse voltammetry measurements. Also, the C6–PAu electrode could be regenerated easily by washing with ethanol, and was reused five times consecutively.

Electrochemical sensor applications of Pt supported porous gold electrode prepared using cellulose-filter

A facile and rapid method for the synthesis of porous gold (PAu) electrodes on cellulose-filters is proposed. Morphology and active surface area of the electrode greatly influence the electrochemical properties of sensor. Compared to smooth electrode and glassy carbon, PAu and Pt/PAu electrode showed high roughness due to porous structure, which is helpful in electrochemical sensing of target molecules. The electrochemical sensing performance of Pt/PAu electrode was evaluated to detect hydrogen peroxide, glucose, and perchloric acid. The amperometric results with various concentrations of target molecules showed potential applications of Pt/PAu electrode in sensitive and effective chemical sensors.

A novel graphene nanodots inlaid porous gold electrode for electrochemically controlled drug release

A uniform graphene nanodots inlaid porous gold electrode was prepared via ion beam sputtering deposition (IBSD) and mild corrosion chemistry. HRTEM, SEM, AFM and XPS analyses revealed the successful fabrication of graphene nanodots inlaid porous gold electrode. The as-prepared porous electrode was used as π-orbital-rich drug loading platform to fabricate an electrochemically controlled drug release system with high performance. π-orbital-rich drugs with amino mioety, like doxorubicin (DOX) and tetracycline (TC), were loaded into the graphene nanodots inlaid porous gold electrode via non-covalent π–π stacking interaction. The amino groups in DOX and TC can be easily protonated at acidic medium to become positively-charged NH3+, which allow these drug molecules to be desorbed from the porous electrode surface via electrostatic repulsion when positive potential is applied at the electrode. The drug loading and release experiment indicated that this graphene nanodots inlaid porous gold electrode can be used to conveniently and efficiently control the drug release electrochemically. Not only did our work provide a benign method to electrochemically controlled drug release via electrostatic repulsion process, it also enlighten the promising practical applications of micro electrode as a drug carrier for precisely and efficiently controlled drug release via embedding in the body.

Graphene nanodots encaged 3-D gold substrate as enzyme loading platform for the fabrication of high performance biosensors

Herein, a uniform three-dimensional (3-D) graphene nanodots-encaged porous gold electrode was prepared via ion beam sputtering deposition (IBSD) and mild corrosion chemistry for efficient enzyme electrode fabrication. Enzymes, like glucose oxidase and catalase, were modified with pyrene functionalities and then loaded into the graphene nanodots encaged porous gold electrode via non-covalent π–π stacking interaction between pyrene and graphene. The fabricated enzyme electrodes showed profound reusability and repeatability, high sensitivity, inherent selectivity and enhanced detection range. As for glucose analysis a broad linear range from 0.05 to 100mM was obtained and the linear range for hydrogen peroxide was 0.005 to 4mM. Detection limits of 30μM for glucose and 1μM for hydrogen peroxide were achieved (S/N=3), respectively. These electrodes can be applied to analyze the clinical samples with reliable results. The formation mechanism and 3-D structure of the porous electrode were investigated using high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). Most importantly, various other ideal biosensors can be fabricated using the same porous electrode and the same enzyme modification methodology.

Electrochemical Behavior of Cytochrome C as a Self-Assembled Monolayer on a Porous Gold Electrode

To understand the electron transfer mechanism of cytochrome C in the intermembrane space of mitochondria, two kinds of electrochemical interfaces, single 3-mercaptopropionic acid self-assembled monolayer modified porous gold electrodes and binary 3-mercaptopropionic acid-octadecanethiol self-assembled monolayer modified porous gold electrodes, were constructed. The binary 3-mercaptopropionic acid-octadecanethiol self-assembled monolayer was prepared by the oxidation of the preassembled 3-mercaptopropionic acid self-assembled monolayer coupled with the replacement reaction of octadecanethiol. Atomic force microscopy showed that both interfaces had relatively uniform pores with dimensions of a few nanometers that mimicked the confined environments of cytochrome C in the intermembrane space of mitochondria. The self-assembly of cytochrome C on the two interfaces occurred via electrostatic interactions between the polar amino acid residues of the cytochrome C molecules and the -COOH terminal groups of the self-assembled monolayer. Electrochemical results showed that cytochrome C at the conductive 3-mercaptopropionic acid self-assembled monolayer modified porous gold electrode displayed enhanced electrochemical activity and a faster electron transfer rate when compared to a gold electrode interface. However, the electron transport behavior of cytochrome C was prevented when the insulated octadecanethiol component was in the self-assembled monolayer. This work suggests that the electrochemical behavior of proteins in confined environments differs from the behavior when unconfined.

Synthesis of paper-based porous gold electrode for electrocatalytic oxidation of ethanol

Herein, to apply porous gold electrode for the electrooxidation of ethanol, we proposed a simple and facile method for the synthesis of paper-based porous gold (PAu) with large surface area using gold nanoparticles (AuNPs) and filter paper. The results showed that Pd/PAu exhibited a large electrochemical surface because of pore size of 100nm and high electrochemical reaction compared to smooth Au foil and PAu. The as-prepared Pd/PAu electrode exhibited high activity and stability for ethanol electrooxidation in alkaline solution and was reusable even after 100 cycles.

Graphene nanodots-encaged porous gold electrode fabricated via ion beam sputtering deposition for electrochemical analysis of heavy metal ions

A graphene nanodots-encaged porous gold electrode via ion beam sputtering deposition (IBSD) for electrochemical sensing is presented. The electrodes were fabricated using Au target, and a composite target of Al and graphene, which were simultaneously sputtered onto glass substrates by Ar ion beam, followed with hydrochloric acid corrosion. The as-prepared graphene nanodots-encaged porous gold electrodes were then used for the analysis of heavy metal ions, e.g. Cu2+ and Pb2+ by Osteryoung square wave voltammetry (OSWV). These porous electrodes exhibited enhanced detection range for the heavy metal ions due to the entrapped graphene nanodots in 3-D porous structure. In addition, it was also found that when the thickness of porous electrode reached 40nm the detection sensitivity came into saturation. The linear detection range is 0.009–4μM for Cu2+ and 0.006–2.5μM for Pb2+. Good reusability and repeatability were also observed. The formation mechanism and 3-D structure of the porous electrode were also investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS). This graphene entrapped 3-D porous structure may envision promising applications in sensing devices.

Glucose Oxidase Directly Immobilized onto Highly Porous Gold Electrodes for Sensing and Fuel Cell applications

The successful implementation of redox-enzyme electrodes in biosensors and enzymatic biofuel cells has been the subject of extensive research.For high sensitivity and high energy-conversion efficiency, the effective electron transfer at the protein-electrode interface has a key role. This is difficult to achieve in the case of glucose oxidase, due to the fact that for this enzyme the redox centre is buried inside the structure, far from any feasible electrode binding sites.This study reports, a simple and rapid methodology for the direct immobilisation of glucose oxidase into highly porous gold electrodes. When the resulting electrode was tested as glucose sensor, a Michaelis-Menten kinetic trend was observed, with a detection limit of 25μM. The bioelectrode sensitivity, calculated against the superficial surface area of the bioelectrode, was of 22.7±0.1μAmM−1cm−2.This glucose oxidase electrode was also tested as an anode in a glucose/O2 enzymatic biofuel cell, leading to a peak power density of 6μWcm−2 at a potential of 0.2V.

Electroassisted codeposition of sol-gel derived silica nanocomposite directs the fabrication of coral-like nanostructured porous gold.

Herein, we report on a one-step coelectrodeposition method to form gold-silica nanocomposite materials from which high surface area nanostructured gold electrodes can be produced. The as-prepared Au-SiO2 films possess an interconnected three-dimensional porous framework with different silica-gold ratios depending on the deposition solutions and parameters. Chemical etching of the nanocomposite films using hydrofluoric acid resulted in the formation of nanostructured porous gold films with coral-like structures and pores in the nanometer range. The cross-linkage of the gold coral branches resulted in the generation of a porous framework. X-ray photoelectron spectroscopy confirms the complete removal of silica. Well-controlled surface area enhancement, film thickness, and morphology were achieved by manipulating the deposition parameters, such as potential, time, and gold ion and sol-gel monomer concentrations in the deposition solution. An enhancement in the surface area of the electrode up to 57 times relative to the geometric area has been achieved. The thickness of the as-prepared Au-SiO2 nanocomposite films is relatively high and varied from 8 to 15 μm by varying the applied deposition potential while the thickness of the coral-like nanostructured porous gold films ranged from 0.22 to 2.25 μm. A critical sol-gel monomer concentration (CSGC) was determined at which the deposited silica around the gold coral was able to stabilize the coral-like gold nanostructures, while below the CSGC, the coral-like gold nanostructures were unstable and the surface area of the nanostructured porous gold electrodes decreased.

Ordered Porous Gold Electrodes to Enhance the Sensitivity of Enzyme-Based Glucose Sensors

Glucose sensors are essential tools for diabetes patients to use in monitoring their blood glucose levels. However, to be able to detect glucose in non-invasively collected physiological fluids, such as tears and urine, the sensitivity of these glucose sensors must be significantly higher than sensors that are currently used to detect glucose concentrations in blood. Increasing the specific surface area of enzyme-based glucose sensors through the use of ordered porous gold electrodes has been shown to enhance the sensitivity of these sensors. The enzyme-based ordered porous gold glucose sensor was demonstrated to be suitable in detecting glucose concentrations ranges that are similar to those occurring in tears. Although sensitivity of the glucose sensor is enhanced, the saturation threshold of the sensor is lowered. Further optimizations of the porous gold electrodes are required to eliminate signal saturation of these improved sensors.

Electrochemical Properties of Nanostructured Porous Gold Electrodes in Biofouling Solutions

The effect of electrode porosity on the electrochemical response of redox active molecules (potassium ferricyanide, ruthenium(III) hexammine, and ferrocene methanol) in the presence of bovine serum albumin or fibrinogen was studied at macroporous (pore diameter: 1200 nm), hierarchical (1200/60 nm), and nanoporous (<50 nm) gold. These electrodes were prepared using standard templating or dealloying techniques, and cyclic voltammetry (CV) was utilized to evaluate the effect of protein adsorption on the electron transfer of the diffusing redox probes. Following exposure to albumin (or fibrinogen) under near neutral pH conditions, planar gold electrodes showed an immediate reduction in Faradaic peak current and increase in peak splitting for potassium ferricyanide. The rate at which the CV curves changed was highly dependent on the morphology of the electrode. For example, the time required for the Faradaic current to drop to one-half of its original value was 3, 12, and 38 min for planar gold, macroporous gold, and hierarchical gold, respectively. Remarkably, for nanoporous gold, only a few percent drop in the peak Faradaic current was observed after an hour in solution. A similar suppression in the voltammetry at planar gold was also noted for ruthenium hexammine at pH 3 after exposure to albumin for several hours. At nanoporous gold, no significant loss in response was observed. The order of performance of the electrodes as judged by their ability to efficiently transfer electrons in the presence of biofouling agents tracked porosity with the electrode having the smallest pore size and largest surface area, providing near ideal results. Nanoporous gold electrodes when immersed in serum or heparinized blood containing potassium ferricyanide showed ideal voltammetry while significant fouling was evident in the electrochemical response at planar gold. The small nanopores in this 3D open framework are believed to restrict the transport of large biomolecules, thus minimizing passivation of the inner surfaces while permitting access to small redox probes to efficiently exchange electrons.

One-step porous gold fabricated electrode for electrochemical impedance spectroscopy immunosensor detection

A porous gold electrode fabricated by a simple one-step electro-process was employed for the first time to enhance a label-free immunosensor detection based on electrochemical impedance spectroscopy (EIS). The porous gold surface was simply fabricated using an applied potential of 1.50V in 100s, providing a 19±1 times larger surface area than the flat gold electrode. The larger surface area enhanced the performance of an immunosensor by increasing the amount of the immobilized antibody. The antibody–antigen pair of anti-human serum albumin (anti-HSA) and human serum albumin (HSA) was use as a model for the direct immunosensor detection. Porous and flat gold electrodes were modified with anti-HSA via a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) and thiourea and a polymer layer of polytyramine and their performance was tested by EIS technique. The effect of two blocking solutions bovine serum albumin (BSA) and 1-dodecanethiol were also tested. The porous electrode modified with anti-HSA via the SAM of 11-MUA and blocked with BSA provided the highest sensitivity and the lowest detection limit, of up to 8.7 times and two order of magnitude compared with the flat electrode, respectively. The electrode can be reused for up to 40 times. The system was used to analyze albumin in serum and urine samples and the results agreed well with the photometric bromocresal green method for serum sample and an immunoturbidimetric assay for urine sample (P>0.05). This method could be easily applied to other label-free affinity pairs.

Highly sensitive electrochemical lead ion sensor harnessing peptide probe molecules on porous gold electrodes

Lead ion is one of the most hazardous and ubiquitous heavy metal pollutants and poses an increasing threat to the environment and human health. This necessitates rapid and selective detection and/or removal of lead ions from various soil and water resources. Recently, we identified several Pb2+ binding peptides via phage display technique coupled with chromatographic biopanning (Nian et al., 2010) where a heptapeptide (TNTLSNN) capable of recognizing Pb2+ with high affinity and specificity evolved. In the present study, an electrochemical sensor harnessing this Pb2+ affinity peptide as a probe on a porous gold electrode was developed. The three dimensional porous gold electrode was obtained from electrochemical deposition using the dynamic hydrogen bubble template method. A thin layer of poly(thiophene acetic acid) (PTAA) was coated on the porous gold surface. The Pb2+ recognizing peptide was immobilized via amide linkage on the PTAA. The developed biosensor was demonstrated to be fast, selective and reproducible in Pb2+ detection, exhibiting Pb2+-specific peak current values around −0.15V in a broad concentration range (1−1×107nM) in 10min despite the repeated use after regeneration.

Hierarchical porous gold electrodes: Preparation, characterization, and electrochemical behavior

Hierarchical porous gold films with a well-defined bimodal architecture have been made by electrodepositing gold at a constant current around a close-packed assembly of raspberry-like latex spheres (1200/60nm) followed by template removal. Electrodeposition was stopped when the gold was either ½ layer or 1½ layer thick as evident from oscillations in the potential vs time traces. Scanning electron microscopy (SEM) images show the hierarchical pore structure with an ensemble of small ∼20nm openings located in a large ∼1200nm diameter macropore. Prior to electrochemical characterization, the electrodes were cleaned either chemically and/or via UV radiation and X-ray photoelectron spectroscopy (XPS) was used to evaluate the presence of residual polystyrene. Of the three cleaning methods investigated, sonication in chloroform–acetone followed by UV radiation proved best. The surface area of the hierarchical porous gold electrodes, determined by integrating the area under the gold oxide peak, was 4× larger than a bare gold electrode and 2× larger than a macroporous gold electrode prepared using unimodal, 1200nm diameter latex spheres as the template. The electrochemical performance of the electrodes relative to the macroporous gold and flat gold was undertaken using cyclic voltammetry. The results show that the non-Faradaic current scales linearly with electrode area while the Faradaic current of a diffusing electrochemically reversible redox probe (ferrocene methanol) does not. For an adsorbed redox couple (ferrocene hexanethiol), the voltammetric wave shapes and surface coverage were different for the different electrodes.

Effect of Ordered Intermediate Porosity on Ion Transport in Hierarchically Nanoporous Electrodes

The high surface area of nanoporous electrodes makes them promising for use in electrochemical double-layer supercapacitors, desalination and pollution remediation, and drug delivery applications. When designed well and operating near their peak power, their charging rates are limited by ion transport through their long, narrow pores. This can be alleviated by creating pores of intermediate diameter that penetrate the electrode. We have fabricated electrodes featuring these by creating colloidal crystal-templated opals of nanoporous gold formed by dealloying. The resulting electrodes contain a bimodal pore-size distribution, with large pores on the order of several 100 nm and small pores on the order of 10 nm. Electrochemical impedance spectrometry shows that porous gold opals sacrifice some capacitance, but possess a lower internal resistance, when compared to a porous gold electrode with only the smaller-diameter pores. The architectural flexibility of this approach provides a greater ability to design a balance between power density and energy density.