Monolayer Modified Gold Electrode Research Articles

Voltametric Behavior of Noradrenaline at 2-Mercaptoethanol Self-Assembled Monolayer Modified Gold Electrode and its Analytical Application

2-Mercaptoethanol self-assembled monolayer (ME/Au SAMs) was prepared on a gold electrode. The ME/Au SAMs was characterized by using ATR-FTIR and dynamic contact angle measurements. The electrochemical behaviors of noradrenaline (NE) on the ME/Au SAMs were studied in BR buffer solution. The modified electrode accelerated electron transfer rate of the redox of NE and showed an excellent eletrocatalytic activity. The diffusion coefficient (D) of NE was obtained to be 4.3×10-8 cm2 s-1. The catalytic current increased linearly with the concentration of NE in the range of 2.0×10-6 -1.0×10-3 M by square wave voltammetry response. The modified electrode could eliminate the interference of ascorbic acid (AA) at 40-fold concentration of NE and could be satisfactorily used for the determination of NE in the drug injection.

Accumulation and stripping behavior of silver ions at dl-dithiothreitol self-assembled monolayer modified gold electrodes

Silver ions can be entrapped at the dl-dithiothreitol (HSCH 2(CHOH) 2CH 2SH, DTT) self-assembled monolayer films modified gold electrodes. When the potential was made moving, an anodic peak was observed at about 0.23 V (vs. SCE). When the electrode Au/DTT was modified with dodecyl mercaptan further, more Ag (I) can be accumulated and the peak grows. Conditions, such as solution pH and supporting electrolyte, were optimized for Ag (I) determination. Under the selected conditions, i.e. 0.010 M pH 4.3 potassium hydrogen phthalate, preconcentration time of 5 min at open circuit, the anodic peak height is linear to the concentration of Ag (I) in the small range of 0.6–2.4 μM. The influence of some ions on the determination of Ag (I) was examined. The Br − ion makes the peak decrease and NCS − makes the peak increase. But the determination is not interfered by 1000-fold Pb 2+, Cd 2+, Hg 2+, Fe 3+, Ni 2+, Co 2+, Cu 2+ and Sn 2+ when EDTA was added into the solution. The mechanism involved was discussed.

Electrochemical detection of hybridization using peptide nucleic acids and methylene blue on self-assembled alkanethiol monolayer modified gold electrodes

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probes is presented. PNA probes were attached covalently through a competition of free amines on the guanine bases and also at the 5 ′ end of the probe, using N-(3-dimethylamino)propyl)- N ′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) onto a carboxylate terminated alkanethiol self-assembled monolayer (SAM) preformed on a gold electrode (AuE). The covalently immobilized probe could selectively hybridize with the target DNA to form a hybrid on the surface despite the bases being attached to the SAM. The changes in the peak currents of methylene blue (3,7-bis(dimethylamino)phenothiazin-5-ium chloride, MB), an electroactive label, were observed upon hybridization of probe with the target. Effective discrimination against point mutation was also obtained. Performance characteristics of the sensor are described, along with future prospects.

Cyclic Voltammetric and Scanning Electrochemical Microscopic Study of Menadione Permeability through a Self-Assembled Monolayer on a Gold Electrode

Menadione (2-methyl-1,4-naphthoquinone) reduction and menadiol oxidation at octadecanethiol (C18SH) monolayer modified gold electrodes were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The modified electrode acts as a better barrier toward the ferrocyanide transport than toward the menadione species. This difference is attributed to permeation of the organic substrates into the hydrophobic monolayer. A simple model is proposed and applied to extract the rate constant of the kinetically limiting permeation step from the cyclic voltammograms. However, a better estimate of the transport properties is obtained by SECM. The same trends are observed with CV and SECM, and a similar pH dependence shows the loss of an intermediate formed during menadione reduction from the monolayer with increasing pH. This loss can probably be assigned to the rapid expulsion of the more hydrophilic reduced species from the monolayer.

Ion-induced discrete charging of immobilized water-soluble gold nanoclusters.

Hydrophilic gold nanoclusters were immobilized onto monolayer-modified gold electrodes and PF6-(-)induced rectification and stepwise capacitance charging was studied in aqueous supporting electrolyte by cyclic voltammetry and ac voltammetry.

Electrocatalytic response of dopamine at a metallothioneins self-assembled gold electrode.

The metallothioneins (MT) self-assembled monolayer modified gold electrode (MT/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k(s)) is 6.97 x 10(-3) cm s(-1) (20 degrees C) at the self-assembled electrode. The electrode reaction is a quasi-reversible process. The oxidation peak of DA can be used to determine the concentration of DA. The peak current and the concentration of DA follow a linear relationship in the range of 2.0 x 10(-5) M to 8.0 x 10(-4) M. The detection limit is 6.0 x 10-6 M. By ac impedance spectroscopy, the apparent electron transfer rate constant (k(app)) of Fe(CN)6(3-)/Fe(CN)6(4-) at the MT/Au electrode was obtained as 2.0 x 10(-5) cm s(-1). The MT/Au was characterized with grazing angle FT-IR spectroscopy and contact angle goniometry.

Electrochemical behavior of epinephrine at l-cysteine self-assembled monolayers modified gold electrode

The electrochemical behaviors of epinephrine (EP) at the l-cysteine self-assembled monolayers modified gold electrode have been studied. The modified electrode shows an excellent electrocatalytic activity for the oxidation of EP and accelerates electron transfer rate. The diffusion coefficient ( D) is 1.48×10 −7 cm 2 s −1. FTIR has shown that cysteine can bind onto the gold surface through the strong sulfur–gold interaction. The electrocatalytic mechanism to EP has been studied. The catalytic current of EP ν s its concentration has a good linear relation in the range of 1.0×10 −7–2.0×10 −6 mol l −1, with the correlation coefficient of 0.9989 by differential pulse voltametric (DPV) response. Detection limit is down to 1.0×10 −8 mol l −1. At a high EP concentration, the relationship between the catalytic current and its concentration exhibits a Michaelis–Menten kinetic mechanism for the electrocatalytic process and the constant K m is about 0.155 mmol l −1. The highest catalytic current I m is 2.72 μA. The modified electrode can be used for the determination of EP in practical injection. The method is simple, quick, sensitive and accurate.

Electrochemical behavior of dopamine and ascorbic acid at osmium(II) complex cationic monolayer modified gold electrodes.

The electrooxidation of dopamine (DA) and ascorbic acid (AA) was studied using gold electrodes modified by a cationic self-assembled monolayer of [Os(bpy)2(bpy-(CH2),3SH)]2+ by cyclic voltammetry. At an [Os(bpy)2(bpy-(CH2)13SH)]2+/Au electrode, the oxidation peak of DA shifted to a much more positive potential as compared with that of a bare gold electrode, while the oxidation peak potential of AA showed a slightly negative shift due to their different electrostatic interactions with the cationic monolayer. Thus, a sufficient potential difference was achieved for distinguishing the electrochemical responses of DA and AA. However, when CH3(CH2)11SH was mixed into the cationic monolayer, the enhanced packing of the mixed monolayer blocked the access of DA or AA to the electrode, resulting in further positive shifts for both oxidation-peak potentials.

Electrocatalytic response of norepinephrine at a thiolactic acid self-assembled gold electrode

The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant ( k s) is 5.11×10 −3 cm s −1 at the self-assembled electrode. The electrode reaction is a pseudo-reversible process. The peak current and the concentration of NE are a linear relationship in the range of 4.0×10 −5–2.0×10 −3 mol l −1. The detection limit is 2.0×10 −6 mol l −1. By ac impedance spectroscopy the apparent electron transfer rate constant ( k app) of Fe(CN) 3−/Fe(CN) 4− at the TLA/Au electrode was obtained as 2.5×10 −5 cm s −1.

The Electrodeposition of Polypyrrole on a Glutathione Self-Assembled Monolayer Modified Gold Electrode and Its Electrochemical Behavior

The Electrodeposition of Polypyrrole on a Glutathione Self-Assembled Monolayer Modified Gold Electrode and Its Electrochemical Behavior

Direct Electrochemistry of Cytochrome c at a Thiolactic Acid Self-Assembled Gold Electrode

The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to promote the direct electrochemistry of cytochrome c by cyclic voltammetry. A pair of well-defined redox waves were obtained at the TLA/Au electrode in cytochrome c aqueous solution. The calculated standard rate constant (ks) is 8.76×10−3 cm/s. The electrode reaction is a reversible process as scan rate is lower than 300 mV/s. The TLA SAM was characterized with grazing angle FT-IR spectroscopy.

The Electrodeposition of Polypyrrole on a Glutathione Self-Assembled Monolayer Modified Gold Electrode and Its Electrochemical Behavior

Cyclic voltammetry and chronoamperometry have been used to investigate the electrochemical deposition of pyrrole at glutathione (GSH) self-assembled monolayer modified gold electrodes (GSH SAM/Au). It is shown that GSH monolayer exhibits great influence on the nucleation and growth of polypyrrole (PPy) at the electrode surface. GSH SAM makes the initial polymeric potential and peak potential shift positively and polymeric amount decrease. It can depress the diffusion of ions into PPy film and lower the background signal. Various conditions such as potential, solution pH, supporting electrolyte and surfactant have been tested. It was found that the polymerization could be facilitated at sufficiently positive potential and high pyrrole concentration. The nucleation and growth of polypyrrole at GSH SAM/Au is seriously affected by the solution pH and the polymerization becomes easy at lower solution pH, which is different from that at the bare gold electrode. The primary properties of the resulting film are discussed as well in this article.

Electrochemically Regulated Iron Uptake and Release for Ferritin Immobilized on Self-Assembled Monolayer-Modified Gold Electrodes

Abstract Horse spleen ferritin was immobilized on self-assembled monolayers (SAMs)-modified gold electrodes by electrostatic interaction. Electrochemically regulated iron uptake and release for the ferritin immobilized on the electrode was demonstrated.

Electrocatalytic response of dopamine at a thiolactic acid self-assembled gold electrode

The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant ( k s) is 0.525 cm/s at the self-assembled electrode. The electrode reaction is a reversible process. The oxidation peak of DA can be used to determine the concentration of DA. The peak current and the concentration of DA have a linear relationship in the range of 4.0×10 −5–8.0×10 −4 mol/l. The detection limit is 3.0×10 −6 mol/l. The TLA-SAM was characterized with X-ray photoelectron spectroscopy (XPS) and a contact angle goniometer.

Langmuir Monolayer Flow across Hydrophobic Surfaces. 2. Sensor Development Using Langmuir Monolayer Flow

Two sensing mechanisms utilizing Langmuir monolayer flow, the pressure-driven movement of a Langmuir film into a hydrophobic surface−liquid interface, have been investigated and involve analyte interaction with either the flowing monolayer or stationary film. The sensing aspect is achieved through modulation of the bilayer formation rate. A sensor using this novel transduction mechanism was developed for Cd2+, based on the interaction of divalent cations with the carboxylic headgroup of the flowing monolayer. Aqueous divalent cations associate with an oleic acid monolayer, increasing its viscosity. As a result, the flow rate of the associated monolayer is slower than for the unassociated monolayer. A rudimentary pH sensor was also developed to exemplify flow-based sensing, in which oleyl alcohol flows into the interface between a mixed methyl-carboxylic acid terminated self-assembled monolayer modified gold electrode and water. The flow rate for this system was sensitive to subphase pH. Attenuation of the...

PH-dependent binding interaction between functionalized thiol monolayers and electroactive ions

The charge transfer kinetics at ionizable thiol monolayer-modified gold electrodes was investigated as a function of the redox-couple composition and the solution pH by potential scan voltammetry and electrochemical impedance spectroscopy. The adsorption of indigotetrasulfonate and chromate onto a 4-aminothiophenol monolayer, at low pH values, resulted primarily from an electrostatic attraction between the protonated terminal amino groups and the anions. An increase in the solution pH, however, raised the apparent heterogeneous rate constant of indigotetrasulfonate at a 4-aminothiophenol-modified electrode. This pH dependence, which was opposite to that observed at a 1-butanethiol-modified electrode, can be ascribed to a change in the potential difference between the gold electrode and monolayer surface. A large change in the heterogeneous rate constant with the pH implies that in addition to electrostatic interaction, a specific intermolecular force contributes to the interactions between the 4-aminothiophenol monolayer and the redox species.

Nanomolar scale nitric oxide generation from self-assembled monolayer modified gold electrodes

A SAM-modified gold electrode has been developed for the first time for quantitative NO generation of a nanomolar amount that is proportional to the surface area of the electrode.

Photocurrent generation at a fullerene self-assembled monolayer-modified gold electrode cast with a polyurethane membrane

Two photoelectrochemical cells based on C60-SAM-modified gold electrodes have been fabricated and their photoelectric responses with Ar- or O2-saturated electrolyte investigated. High quantum yields under visible light illumination and without an external electron sacrificer were observed. A new approach consisting of casting an ion-selective polyurethane membrane on the C60-SAM leads to improved stability of the photocurrent generation.

Electrochemical Study of a Polypyrrole Film/Decanethiol Self-Assembled Monolayer on a Gold Electrode

Cyclic voltammetry and chronoamperometry were used to study the deposition of polypyrrole on a decanethiol self-assembled monolayer modified gold electrode (PPY/SAM/Au). The voltammetric behavior of the PPY/SAM film was investigated in the presence of several different electrolytes. It is found that the SAM shows great influence on the nucleation and growth of the PPY film. The reaction of the SAM and the anions causes the different voltammetric behavior of the polymerization of pyrrole on the modified electrode. Chronoamperometry shows the nucleation and growth of the PPY is initially inhibited but followed by a rapid increase. The SAM also influences electrochemical behavior of PPY film. Experiments show that the SAM can greatly depress the diffusion of anions in the PPY film, and minimize the background capacitance current.

Electrochemical Study of a Polypyrrole Film/Decanethiol Self-Assembled Monolayer on a Gold Electrode

Cyclic voltammetry and chronoamperometry were used to study the deposition of polypyrrole on a decanethiol self-assembled monolayer modified gold electrode (PPY/SAM/Au). The voltammetric behavior of the PPY/SAM film was investigated in the presence of several different electrolytes. It is found that the SAM shows great influence on the nucleation and growth of the PPY film. The reaction of the SAM and the anions causes the different voltammetric behavior of the polymerization of pyrrole on the modified electrode. Chronoamperometry shows the nucleation and growth of the PPY is initially inhibited but followed by a rapid increase. The SAM also influences electrochemical behavior of PPY film. Experiments show that the SAM can greatly depress the diffusion of anions in the PPY film, and minimize the background capacitance current.