Monolayer Modified Gold Electrode Research Articles

Voltammetric-based immunosensing of Newcastle disease virus on polyethylene glycol-containing self-assembled monolayer modified gold electrode

A voltammetric immunosensor for the detection of Newcastle disease virus (NDV) has been developed by employing polyclonal antibody targeting NDV (anti-NDV) as a bioreceptor. Anti-NDV was immobilized on polyethylene glycol (PEG)-containing self-assembled monolayer (SAM) which was activated with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimidehydrochloride (EDC) and N-hydroxy succinimide (NHS) coupling on screen-printed gold electrode (SPGE). The introduction of PEG-containing SAM on the SPGE allowed the bioreceptor to covalently bound to the electrode surface whilst still providing a hydrophilic layer on the electrode which is important to greatly reduce non-specific bindings. The bioreceptor functionalized electrode was then allowed to be incubated with NDV-spiked samples. The electrode surface modification with PEG-containing SAM, immobilization of anti-NDV as bioreceptor, up to the detection of NDV were characterized electrochemically through differential pulse voltammetry (DPV) analysis in [Fe(CN)6]3- as the redox probe. Decrement of anodic current peak (Ipa) of [Fe(CN)6]3- was seen as the concentration of NDV increased from 0.156 to 20 HA μL-1 with the limit of detection (LoD) of 1.50 HA μL-1 at 3σ m-1. The detection of NDV in HA μL-1 unit in this study would ease interlaboratory interpretation as it was the same unit used in hemagglutination (HA) assay of conventional NDV diagnosis. The specificity of anti-NDV used as bioreceptor towards NDV was confirmed through western blot analysis, whilst the selectivity of the bioreceptor-functionalized electrode has been tested with allantoic fluid as the negative control in which no apparent changes of anodic peak (Ipa) has been seen. This simple, fast, and less laborious electrochemical detection method could become an alternative to the conventional method for NDV detection.

Single-Electron Charging of Thioctic Acid Monolayer-Protected Gold Clusters.

There is great interest in the use of Monolayer-Protected Gold Clusters (AuMPCs) as nanoscale capacitors in aqueous media for nanobiotechnological applications, such as bioelectrocatalysts, biofuel cells, and biosensors. However, AuMPCs exhibiting subattofarad double-layer capacitance at room temperature, and the resolution of single-electron charging, has been mainly obtained in an organic medium with nonfunctional capping ligands. We report here the synthesis of Thioctic Acid Monolayer-Protected Au Clusters (TA-AuMPCs) showing electrochemical single electron quantized capacitance charging in organic and aqueous solutions and when immobilized onto different self-assembled monolayer-modified gold electrodes. The presence of functional carboxylic groups opens a simple strategy for interfacing a nanoparticle assembly to biomolecules for their use as electron donors or acceptors in biological electron transfer reactions.

Preparation a novel 1-pyreneacetic acid functionalized graphene/self-assembled monolayer modified gold electrode to immobilize and study interfacial electron transfer of cytochrome c by electrochemical approaches

A new hybrid of favorable orientated cytochrome c (cyt c) and a 1-Pyreneacetic acid (PA) functionalized graphene (Gr) on Au electrode (AuE) was prepared. In the hybrid system, Gr was functionalized with (PA) molecule through π-π interaction (PA-Gr). Afterward the PA-Gr attached to the AuE via Thionalide self-assembled monolayer (SAM), then conjugated with cyt c. The AuE/SAM/PA-Gr/cyt c hybrid system was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) techniques. SECM approach curves were applied to measure the standard tunneling electron transfer (ET) and bimolecular rate constants which were 56.6 s−1 and 1 × 109cm3mol−1 s−1, respectively.

Electrochemical detection of DNA by formation of efficient electron transfer pathways through adsorbing gold nanoparticles to DNA modified electrodes

The high-performance detection of nucleic acids is increasingly important in the early and accurate disease diagnosis. Herein, we describe a unique label-free electrochemical DNA biosensor, which is based on gold nanoparticles (GNPs) mediated electron transfer through a DNA monolayer modified gold electrode surface. We observed that the different states of DNA monolayers (single-strand DNA or triple-helix DNA) and the different sizes of GNPs have a significant effect on the electron transfer by the DNA modified gold electrodes. This DNA biosensing strategy avoids the complicated fabrication process of the DNA capture probes and minimizes the steps of electrode pre-treatment. Under optimal conditions, this method can sensitively and accurately detect the target DNA ranging from 10 pM to 100 nM with a detection limit of 1.47 pM.

A heterogeneous bio-inspired peroxide shunt for catalytic oxidation of organic molecules.

Heme enzymes are capable of catalytically oxidising organic substrates using peroxide via the formation of a high-valent intermediate. Iron porphyrins with three different axial ligands are created on self-assembled monolayer-modified gold electrodes, which can oxidize C-H bonds and epoxidize alkenes efficiently. The kinetic isotope effects suggest that the hydrogen atom transfer reaction by a highly reactive oxidant is likely to be the rate-determining step. Effect of different axial ligands and different secondary structures of the iron porphyrin confirms that the thiolate axial ligand with a hydrophobic distal pocket is the most efficient for this oxidation chemistry.

Characterization of the Iron Species Released by Ferritin Immobilized on Self-Assembled Monolayer Modified Gold Electrodes

Iron is released following electrochemical reduction of immobilized ferritin. In this work, voltammetry is used to elucidate the identity of the released iron. Ferritin was covalently immobilized on 6-mercaptohexanoic acid modified gold electrodes. The current-potential curve shows an initial cathodic peak indicating the reduction of ferritin. The return scan gives an anodic peak that is probably due to the oxidation of released Fe(H2O)62+. The second cycle shows a new cathodic wave suggesting the reduction of the iron species. Voltammetry, while stirring the cell solution, reveals that the released iron is dissolved while the oxidized form is immobilized. The cathodic peak potential of the oxidized iron species has a dependence of 120 mV/pH indicating a two-proton exchange per electron transferred, suggesting that Fe(H2O)62+ is oxidized to Fe(OH)2+. Results from voltammetric scans in the presence of hesperitin, Trolox, and maltol further suggest that the oxidized form of iron is Fe(OH)2+.

Characterization of Covalently Bound Anti-Human Immunoglobulins on Self-Assembled Monolayer Modified Gold Electrodes.

Bioconjugated gold surfaces constitute interesting platforms for biosensing applications. The immobilization of antibodies such as anti-immunoglobulin G and M (anti-IgG and anti-IgM) on gold electrodes via self-assembled monolayers (SAMs) is here studied as a model system for further immunoassays development. The biolayer is characterized by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), a dedicated thin-film transistor (TFT)-based platform and electrochemical surface plasmon resonance (EC-SPR). XPS analysis confirms the presence of all the chemical species involved in the fabrication process as well as the covalent attachment of the antibodies with high reproducibility. Visualization of the biolayer topography by AFM shows nanostructures with a thickness consistent with the actual size of the protein, which is also verified by SPR measurements. EC-SPR allows taking advantage of complementary electrochemical and optical signals during the functionalization steps. Moreover, the functionalization of gold leads to a change in the work function, which is demonstrated in an electrolyte gated thin-film transistor configuration. Such configuration enables also to evaluate the electrostatic changes occurring on the gate that are connected with the threshold voltage shifts. The data support that functional biomodified gold surfaces can be reproducibly prepared, which is a prerequisite for further biosensor development.

Effective Electrochemistry of Human Sulfite Oxidase Immobilized on Quantum-Dots-Modified Indium Tin Oxide Electrode.

The bioelectrocatalytic sulfite oxidation by human sulfite oxidase (hSO) on indium tin oxide (ITO) is reported, which is facilitated by functionalizing of the electrode surface with polyethylenimine (PEI)-entrapped CdS nanoparticles and enzyme. hSO was assembled onto the electrode with a high surface loading of electroactive enzyme. In the presence of sulfite but without additional mediators, a high bioelectrocatalytic current was generated. Reference experiments with only PEI showed direct electron transfer and catalytic activity of hSO, but these were less pronounced. The application of the polyelectrolyte-entrapped quantum dots (QDs) on ITO electrodes provides a compatible surface for enzyme binding with promotion of electron transfer. Variations of the buffer solution conditions, e.g., ionic strength, pH, viscosity, and the effect of oxygen, were studied in order to understand intramolecular and heterogeneous electron transfer from hSO to the electrode. The results are consistent with a model derived for the enzyme by using flash photolysis in solution and spectroelectrochemistry and molecular dynamic simulations of hSO on monolayer-modified gold electrodes. Moreover, for the first time a photoelectrochemical electrode involving immobilized hSO is demonstrated where photoexcitation of the CdS/hSO-modified electrode lead to an enhanced generation of bioelectrocatalytic currents upon sulfite addition. Oxidation starts already at the redox potential of the electron transfer domain of hSO and is greatly increased by application of a small overpotential to the CdS/hSO-modified ITO.

An electrochemical biosensor based on cobalt nanoparticles synthesized in iron storage protein molecules to determine ascorbic acid.

The electrochemical detection of ascorbic acid (AA) was investigated using a cobalt(III)-ferritin immobilized on a self-assembled monolayer modified gold electrode in phosphate buffer solution (pH7.5). The modified electrode showed excellent electrochemical activity for oxidation of AA. The response to AA on the modified electrode was examined using cyclic and differential pulse voltammetry techniques. The resulting biosensor showed a linear response to AA in a concentration range from 6.25×10-6 to 2.31×10-5 M with sensitivity of 86,437 μAM-1 and detection limit of 4.65 × 10-6 M based on a signal-to-noise ratio of 3. Electrochemical parameters including the charge transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (ks ) for AA were found to be 0.52 and 1.054 Sec-1 , respectively. It has been shown that, using this modified electrode, AA can be determined with high sensitivity, low detection limit, and high selectivity.

Molecular recognition based on an electrochemical sensor of per(6-deoxy-6-thio)-β-cyclodextrin self-assembled monolayer modified gold electrode

This paper describes the preparation and characterization of a self-assembled monolayer of per(6-deoxy-6-thio)-β-cyclodextrin (β-CD-SH) on a gold electrode surface and the study of its inclusion interactions with d- and l-phenylalanine (Phe). The β-CD-SH was self-synthesized and characterized by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR). The modified electrode surface was carefully characterized by cyclic voltammetry (CV) using potassium ferricyanide ([Fe(CN)6]3−/4−) and ferrocenecarboxylic acid (Fc-COOH) as redox probes. Phe was labeled with gold nanoparticles (n-Au-Phe), and the chiral recognition between them and β-CD-SH on the surface of an electrode was carried out. The methods of gold labeling and silver staining was strengthened by SEM. Finally, silver enhancement was monitored by differential pulse voltammetry (DPV). The DPV signal was greatly amplified by the silver atoms coated on the n-Au. The proposed method distinguished d- from l-Phe with an enantioselectivity coefficient of 3.64. The association constants of o-, m- and p-ABA with β-CD-SH at pH 4.0 were calculated to be 2.84×104, 1.94×104, and 3.43×105mol−1L, respectively.

Sensitive electrochemical biosensing of H2O2 based on cobalt nanoparticles synthesised in iron storage protein molecules, ferritin.

In this report, a highly sensitive electrochemical biosensor based on cobaltferritin immobilised on a self-assembled monolayer modified gold electrode for determination of hydrogen peroxide (H2O2) in phosphate buffer solution (pH 7.5) was investigated. The modified electrode showed excellent electrochemical activity for oxidation of H2O2. The response to H2O2 on the modified electrode was examined using linear sweep and differential pulse voltammetries. In phosphate buffer (pH 7.5, 0.1 M), the fabricated biosensor exhibited a linear dependence (R = 0.989) on the concentration of H2O2 from 2.49 × 10(-9) to 1.91 × 10(-8) M, a high sensitivity of -0.4099 µA/nM and detection limit of 2.48 × 10(-9) based on a signal-to-noise ratio of 3. Charge transfer coefficient (α) and the exchange current (i0) of oxidation for H2O2 were found to be 0.57 and 7.55 A, respectively. It has been shown that, this modified electrode is able to determine H2O2 with a high sensitivity, low detection limit and high selectivity.

Distance Dependent Sensing Capabilities of Enzymatic Biosensor Surface Constructed with Gold Nanoparticle Immobilized on Self Assembled Monolayer Modified Gold Electrode

Distance Dependent Sensing Capabilities of Enzymatic Biosensor Surface Constructed with Gold Nanoparticle Immobilized on Self Assembled Monolayer Modified Gold Electrode

A study of the electron transfer inhibition on a charged self-assembled monolayer modified gold electrode by odd random phase multisine electrochemical impedance spectroscopy

The interest of self-assembled monolayers (SAM) comes from their wide range of very specific technological applications. The SAMs having a terminal charged group are of great importance as model surfaces for electron transfer studies. The electron transfer for highly charged electroactive ions at a SAM modified electrode involves an electrostatic interaction. The present work studies a negatively charged SAM of 2-mercaptobenzimidazole-5-sulfonate (MBIS). The adsorption of the molecule on polycrystalline gold is described by X-ray photoelectron spectroscopy (XPS) and the reductive desorption of MBIS. The behavior of the MBIS monolayer towards the electron transfer of the ferri/ferrocyanide reaction is investigated by cyclic voltammetry and odd random phase multisine electrochemical impedance spectroscopy (ORP-EIS). This technique ensures reliable experiments and enables a statistically founded modeling. The combined electrochemical and surface study allows the investigation of the characteristics and electrochemical properties of the MBIS monolayer formed on polycrystalline gold to provide a quantitative modeling, which is physically and statistically validated. The major contribution of this work is the use of ORP-EIS and XPS to understand how the interaction between a charged SAM and electroactive ions affects the electron transfer.

Electrochemical detection of adenine and guanine using a self-assembled copper(ii)–thiophenyl-azo-imidazole complex monolayer modified gold electrode

A self-assembled copper(ii)–thiophenyl-azo-imidazole complex monolayer modified gold electrode exhibits an excellent electrochemical sensing ability towards adenine and guanine at physiological pH.

Direct electrochemistry and intramolecular electron transfer of ascorbate oxidase confined on l-cysteine self-assembled gold electrode

A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry.A well-defined redox wave centered at 166±3mV (vs. Ag│AgCl│KCl(sat.)) was observed in 5.0mM phosphate buffer solution (pH7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE.Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41×10−11molcm−2 with the apparent adsorption coefficient of 1.63×106Lmol−1. The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function.

Fabrication of a Polyaniline Ultramicroelectrode via a Self Assembled Monolayer Modified Gold Electrode

Herein, we report a simple and inexpensive way for the fabrication of an ultramicroelectrode and present its characterization by electrochemical techniques. The fabrication of polyaniline UME involves only two steps: modification of a gold (Au) electrode by self assembled monolayers (SAM) and then electrodeposition of polyaniline film on this thiol-coated Au electrode by using cyclic voltammetry and constant potential electrolysis methods. Two types of self-assembled monolayers (4-mercapto-1-butanol, MB, and 11-mercaptoundecanoic acid, MUA) were used, respectively, to see the effect of chain length on microelectrode formation. Microelectrode fabrication and utility of the surface was investigated by cyclic voltammetric measurements in a redox probe. The thus prepared polyaniline microelectrode was then used for DNA immobilization. Discrimination between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) was obtained with enhanced electrochemical signals compared to a polyaniline-coated Au electrode. Different modifications on the electrode surfaces were examined using scanning electron microscopy (SEM).

Glucose Biosensor Based on Immobilization of Glucose Oxidase on Silica Nanoparticles Modified Au Electrode

A feasible method to fabricate glucose biosensor was developed by covalent attachment of glucose oxidase (GOx) to a silica nanoparticle monolayer modified gold electrode. Electrochemical impedance spectroscopy (EIS) of ferrocyanide followed the assembly process and verified the successful immobilization of GOx on silica nanoparticle modified on gold electrodes. Cyclic voltammetry (CV), performed in the presence of excess glucose and artificial redox mediator (ferrocenemethanol), allowed to quantify the surface concentration of electrically wired enzyme. The signal of proposed electrode was more than 2.5 times of that on electrode lacking silica nanoparticles. As a result, silica nanoparticles are a good biocompatible solid support for enzyme immobilization.

Electrochemical Studies of Ochratoxin A Mycotoxin at Gold Electrodes Modified with Cysteamine Self‐Assembled Monolayers. Its Ultrasensitive Quantification in Red Wine Samples

AbstractThe quantification of ochratoxin A is studied at cysteamine self‐assembled monolayer modified gold electrodes in red wine samples by square wave voltammetry. Detection and quantification limits of 0.004 µg L−1 and 0.012 µg L−1, respectively, were determined. The recovery percentages were in the range from 146 % to 94.0 % at spiking levels ranging from 0.02 to 5 µg L−1. The variation coefficients for within‐laboratory repeatability varied from 31.4 to 11.5 % for spiked level from 0.02 to 2.0 µg L−1. The developed electrochemical method is efficient, reproducible, and ultrasensitive for the quantification of OTA in red wine samples.

Study of Heterogeneous Electron Transfer on the Graphene/Self-Assembled Monolayer Modified Gold Electrode by Electrochemical Approaches

The electrochemical behaviors of graphene sheets attached to a self-assembled monolayer (SAM) on a gold electrode have been investigated. A gold electrode is sequentially modified by the SAM of n-octadecyl mercaptan (C18H37SH), followed by controllable adsorption of graphene sheets to obtain a graphene/SAM modified Au electrode. The graphene/SAM modified Au electrode is characterized electrochemically by using ruthenium hexaammine (Ru(NH3)63+) as a redox probe, and by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The experimental results indicate that the heterogeneous electron transfer (ET) blocked by the SAM can be restored by graphene sheets and that the graphene/SAM modified Au electrode has a smaller interfacial capacitance, as compared with that of a bare Au electrode. The apparent ET rate constant of Ru(NH3)63+, kapp, on the graphene/SAM modified Au electrode has been also evaluated quantitatively by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), and...

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10−6−1 × 10−3 M to UA and 2 × 10−6−8 × 10−4 M to AA could be obtained at L-cys/GNP/GCE.