Self-assembled Monolayer Modified Gold Electrode Research Articles

Preparation and optimization of a bienzymic biosensor based on self-assembled monolayer modified gold electrode for alcohol and glucose detection

The aim of this project was to develop a bienzymic biosensor, which was based on co-immobilization of alcohol oxidase and glucose oxidase on the same electrode by formation of self-assembled monolayer (SAM) for selective determination of ethanol and glucose. In the biosensor construction the enzymes and the mediator, tetrathiafulvalene (TTF), were immobilized with cross-linking agents glutaraldehyde and cysteamine by forming a self-assembled monolayer (SAM) on a gold disc electrode. Amounts of ethanol and glucose were amperometrically detected by monitoring current values at reduction potential of TTF +, 0.1 V. Decreases in biosensor responses were linearly related to glucose concentrations between 0.1 and 1.0 mM and ethanol concentrations between 1.0 and 10 mM. Limits of detection of the biosensor for ethanol and glucose were calculated to be 0.75 and 0.03 mM, respectively. In the optimization studies of the biosensor some parameters such as optimum pH, optimum temperature, enzyme amount, effect of TTF concentration and duration of SAM formation were investigated.

Application of peptide nucleic acids containing azobenzene self-assembled electrochemical biosensors in detecting DNA sequences

Hybridization of peptide nucleic acids probe containing azobenzene (NH2-TNT4, N-PNAs) with DNA was performed by covalently immobilizing of NH2-TNT4 in sequence on the 3-mercaptopropionic acid self-assembled monolayer modified gold electrode with the helps of N-(3-dimethylaminopropy1)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), and the hybrid was coded as N-PNAs/DNA. Using [Fe(CN)6]4−/3− (1:1) as the electrochemical indicator, the electrochemical properties of the N-PNAs self-assembled monolayer (N-PNAs-SAMs) and N-PNAs/DNA hybridization system under the conditions of before and after UV light irradiation were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectra (EIS). Results showed that the redox currents decreased with the increase of irradiation time, suggesting that the ability of the charge transfer on the electrode surface was weakened and the conformation of hybrid system had been changed, and the control of PNAs/DNA hybridization could be realized by UV light irradiation.

Diffusional Electrochemistry of Cytochrome c on Mixed Captopril/3-Mercapto-1-propanol Self-Assembled Monolayer Modified Gold Electrodes

Well-defined, quasi-reversible, and diffusion controlled electrochemistry of cytochrome c (cyt c) has been observed at a gold electrode modified with a novel mixed captopril/3-mercapto-1-propanol self-assembled monolayer (SAM) in an aqueous solution. An exchange rate constant of 1.4 × 10−3 cm/s, an electron transfer coefficient of 0.52, a diffusion coefficient of 7.8 × 10−7 cm2/s, an apparent number of electrons transferred of 0.98, and formal potential of 0.076 V vs Ag|AgCl (in saturated KCl) were obtained for the reaction from complete kinetic and thermodynamic analyses of the impedance data obtained using Fourier transform electrochemical impedance spectroscopic experiments. The differential pulse voltammetric peak currents show an excellent linearity with the cyt c concentration in a range of 5.0 × 10−6 to 5.0 × 10−4 M at the mixed SAM modified gold electrode.

Charge-Transfer Patterns for [Ru(NH3)6]3+/2+ at SAM Modified Gold Electrodes: Impact of the Permeability of a Redox Probe

Electrochemical performance of a (Ru(NH3)6) 3+/2+ redox couple at gold electrodes modified by alkanethiol self assembled monolayer (SAM) films of the type (-SH -(CH2)n - CH3) with different number of methylene units (n = 2 to 10) in the presence and absence of glucose additives has been studied using fast scan cyclic and steady-state voltammetry. Specific scatter of measured rate constants caused by enhanced sensitivity of this probe to minor defects of SAMs has been observed in a general agreement with the published data for thicker SAMs (n = 9 to 18). In addition, we have disclo- sed the anomalous viscosity-imposed drop of the heterogeneous rate constant for the case of Au electrodes modified by thinner n-alkanethiol SAMs (n = 2, 4). Taking into the account the fact of (Ru(NH3)6) 3+/2+ couple's capability to penetrate into the SAM interior, we ascribe the obtained results to the manifestation of the solvent-friction mechanism under the condition where the redox species presumably together with a few of solvating water molecules reside in a SAM's peri- pheral interior marked by much higher local viscosity (slower dielectric relaxation) compared to the electrolyte solution.

Electrochemical Behaviors of Methylene Blue on DNA Modified Electrode and Its Application to the Detection of PCR Product from NOS Sequence.

An electrochemical DNA biosensor for the detection of NOS gene sequences from genetically modified organisms (GMOs) is presented in this paper. Single-stranded DNA (ssDNA) was covalently attached through the carboxylate ester formed by the 3′-hydroxy end of the DNA with the carboxyl of a mercaptoacetic acid self-assembled monolayer-modified gold electrode using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) as linkers. The electrochemical behavior of methylene blue (MB) on the ssDNA and dsDNA modified gold electrode were carefully studied. Compared with ssDNA/Au electrode, an increase of redox peak current of MB on dsDNA/Au electrode was found, which could be further used for monitoring the recognition of DNA hybridization. Based on this result, the polymerase chain reaction (PCR) product of the common inserts NOS terminator from real GMOs samples was detected successfully.

Label-Free Detection of Antibody−Antigen Interactions on (R)-Lipo-diaza-18-crown-6 Self-Assembled Monolayer Modified Gold Electrodes

Novel (R)-diaza-18-crown-6 has been prepared by a simple two-step synthetic method and characterized for its ability to form a uniform self-assembled monolayer (SAM) on gold as well as to immobilize proteins using atomic force microscopy, quartz crystal microbalance, and electrochemical impedance spectroscopy (EIS) experiments. The (R)-lipo-diaza-18-crown-6 was shown to form a well-defined SAM on gold, which subsequently captures the antibody (Ab) molecules that in turn capture the antigen (Ag) molecules. The Ab molecules studied include antibody C-reactive protein (Ab-CRP) and antibody ferritin (Ab-ferritin) along with their Ag's, i.e., CRP and ferritin. Quantitative detection of the Ab-Ag interactions was accomplished by EIS experiments with a Fe(CN)6(3-/4-) redox probe present. The ratios of the charge-transfer resistances for the redox probe on the SAM-antibody-covered electrode to those with the antigen molecules attached show an excellent linearity for log[Ag] with lower detection limits than those of other SAMs for the electrochemical sensing of proteins.

Amperometric DNA quantification based on the use of peroxidase-mercaptopropionic acid-modified gold electrodes

An electrochemical biosensor, constructed by immobilization of the enzyme horseradish peroxidase (HRP) by cross-linking atop a 3- mercaptopropionic acid (MPA) self-assembled monolayer modified gold electrode, was employed for the amperometric detection of ss- and ds-calf thymus DNA. The catalytic reduction of methylene blue (MB) at the biosensor in the presence of H2O2 was used as the analytical signal, and both batch and flow injection modes were evaluated. Experimental variables concerning both, the biosensor design and the detection process were investigated for an optimum analytical performance in both cases. The biosensor response to calf-thymus ds-DNA was approximately 3-fold lower than that to ss-DNA, indicating a much more favorable binding event of MB with free guanine bases in the ss-DNA. A linear calibration graph for calf-thymus ss-DNA over the 0.8-7.2 mg L −1 concentration range was obtained. Fifty successive injections of 6 mg L −1 ss-DNA yielded a RSD value for ip of 5.5% under flow injection conditions. No significant worsening in the analytical characteristics towards ss-DNA determination was observed under the hydrodynamic conditions. As a potential application of the FI methodology, the possibility of sulfonamides detection through their competition with MB for the DNA binding sites was demonstrated. © 2008 Elsevier B.V. All rights reserved.

Immunosensor for the determination of Staphylococcus aureus using a tyrosinase–mercaptopropionic acid modified electrode as an amperometric transducer

An amperometric immunosensor for the quantification of Staphylococcus aureus based on the coimmobilization of rabbit immunoglobulin G (RbIgG) and tyrosinase on a mercaptopropionic acid self-assembled monolayer modified gold electrode is reported. A competitive mode in which protein-A-bearing S. aureus cells and antiRbIgG labeled with alkaline phosphatase (AP) compete for the binding sites of immobilized RbIgG was used. Monitoring of the affinity reaction was carried out by the amperometric detection at -0.15 V of phenol generated in the enzyme reaction with AP, at the tyrosinase-modified electrode through the electrochemical reduction of the o-quinone formed. Optimization of the working variables, such as the immunosensor composition and incubation times, the applied potential, the working pH and the concentration of phenyl phosphate used as the AP substrate, was carried out. Under the optimized conditions, both the repeatability of the measurements and the reproducibility of the responses obtained with different immunosensors yielded relative standard deviation values for the steady-state current lower than 10%. The immunosensor showed a dynamic range from 4.4x10(5) to 1.8x10(7) S. aureus cells mL(-1), with a detection limit of 1.7x10(5) cells mL(-1). The limit of detection was remarkably improved by subjecting S. aureus cells to wall lysis by heat treatment. The value obtained was 2.3x10(3) cells mL(-1), which is adequate for the monitoring of S. aureus contamination levels in some foodstuffs. As an application, milk samples spiked with bacteria at the 4.8x10(3) cells mL(-1) level were analyzed.

Recognition and detection of ssDNA using 2-mercaptobenzothiazole self-assembled monolayer modified gold electrode

A novel method for sensitive detection of single-stranded DNA (ssDNA) using 2-mercaptobenzothiazole (MBT) self-assembled monolayer (SAM) modified gold electrode (Au-MBT) has been developed. Based on the intercalating effect of MBT into double stranded DNA (dsDNA), Au-MBT electrode possessed the ability to distinguish ssDNA and dsDNA. Cyclic voltammetry (CV) was used to preliminarily characterize the MBT self-assembled monolayer on gold electrode. In the mixture of excessive probe ssDNA and target ssDNA, current signal recorded by differential pulse voltammetry (DPV) after DNA hybridization reflected the extent of the hybridization. Definite relations were observed between the reductive peak currents and the concentration of target ssDNA. The quantitative detection of target ssDNA was achieved with a linear range from 1.59 × 10−8 to 2.4 × 10−6 mol/L. The detection limit was 2.38 × 10−9 mol/L (3σ, n = 11). The Au-MBT electrode possessed high reusability and reproducibility, no significant deterioration of peak currents occurring over 10 detection/regeneration cycles. Combined with the advantages of simplicity and low-cost, the developed electrochemical biosensor shows potential in continuous and quantitative detection of ssDNA in biological samples.

Sensitive voltammetric detection of clomipramine at 16-mercapto-hexadecanoic acid self-assembled monolayer modified gold electrode

Clomipramine, an effective and important antipsychotic drug with low redox activity and poor hydrophilicity, was found to effectively accumulate on hydrophobic 16-mercaptohexadecanoic acid (i.e. MHA) self-assembled monolayer (SAM) modified gold electrode (i.e. MHA/Au) and generating a sensitive anodic peak at about 0.86 V (vs. SCE) in 0.05 M Tris–HCl (pH = 8.1) buffer solution. Thus, quantitative measurement of clomipramine was established with high sensitivity under optimum conditions. The anodic peak current was linear to clomipramine concentration in the range from 1 × 10−6 to 5 × 10−5 M, with a detection limit of 6 × 10−9 M. This method was successfully applied to the detection of clomipramine in drug tablets and proved to be reliable compared to UV. The spectral features, electrochemical characteristics and wettability of MHA-SAM were also studied.

Determination of Ddopamine and Ascorbate on Gold Nanoparticle and 4,4-bis (methanethiol) biphenyl (MTP) Self-assembled Monolayer Modified Gold Electrode

Determination of Ddopamine and Ascorbate on Gold Nanoparticle and 4,4-bis (methanethiol) biphenyl (MTP) Self-assembled Monolayer Modified Gold Electrode

DNA sensor based on an Escherichia coli lac Z gene probe immobilization at self-assembled monolayers-modified gold electrodes

A novel approach to construct an electrochemical DNA sensor based on immobilization of a 25 base single-stranded probe, specific to E. coli lac Z gene, onto a gold disk electrode is described. The capture probe is covalently attached using a self-assembled monolayer of 3,3′-dithiodipropionic acid di( N-succinimidyl ester) (DTSP) and mercaptohexanol (MCH) as spacer. Hybridization of the immobilized probe with the target DNA at the electrode surface was monitored by square wave voltammetry (SWV), using methylene blue (MB) as electrochemical indicator. Variables involved in the sensor performance, such as the DTSP concentration in the modification solution, the self-assembled monolayers (SAM) formation time, the DNA probe drying time atop the electrode surface and the amount of probe immobilized, were optimized. A good stability of the single- and double-stranded oligonucleotides immobilized on the DTSP-modified electrode was demonstrated, and a target DNA detection limit of 45 nM was achieved without signal amplification. Hybridization specificity was checked with non-complementary and mismatch oligonucleotides. A single-base mismatch oligonucleotide gave a hybridization response only 7 ± 3%, higher than the signal obtained for the capture probe before hybridization. The possibility of reusing the electrochemical genosensor was also tested.

Electrochemical behavior of uric acid at a penicillamine self-assembled gold electrode

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The electrode can enhance the electrochemical response of uric acid (UA), and the electrochemical reaction of UA on the PCA electrode has been studied by cyclic voltammetry and differential pulse voltammetry. Some electrochemical parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient and proton transfer number have been determined for the electrochemical behavior on the PCA self-assembled monolayer electrode. The electrode reaction of UA is an irreversible process, which is controlled by the diffusion of UA with two electrons and two protons transfer at the PCA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range of 6.0 × 10−5–7.0 × 10−4 mol L−1 and 2.0 × 10−5–7.0 × 10−4 mol L−1 for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 5.0 × 10−6 and 3.0 × 10−6 mol L−1, respectively. The method can be applied to determine UA concentration in real samples.

Integrated Electrochemical Gluconic Acid Biosensor Based on Self-Assembled Monolayer-Modified Gold Electrodes. Application to the Analysis of Gluconic Acid in Musts and Wines

An integrated amperometric gluconic acid biosensor constructed using a gold electrode (AuE) modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) on which gluconate dehydrogenase (GADH, 0.84 U) and the mediator tetrathiafulvalene (TTF, 1.5 micromol) were coimmobilized by covering the electrode surface with a dialysis membrane is reported. The working conditions selected were Eapp=+0.15 V and 25+/-1 degrees C. The useful lifetime of one single TTF-GADH-MPA-AuE was surprisingly long. After 53 days of continuous use, the biosensor exhibited 86% of the original sensitivity. A linear calibration plot was obtained for gluconic acid over the 6.0x10(-7) to 2.0x10(-5) M concentration range, with a limit of detection of 1.9x10(-7) M. The effect of potential interferents (glucose, fructose, galactose, arabinose, and tartaric, citric, malic, ascorbic, gallic, and caffeic acids) on the biosensor response was evaluated. The behavior of the biosensor in a flow-injection system in connection with amperometric detection was tested. The analytical usefulness of the biosensor was evaluated by determining gluconic acid in wine and must samples, and the results obtained were validated by comparison with those provided by using a commercial enzyme test kit.

Sensitive determination of fluphenazine at a dodecanethiol self-assembled monolayer-modified gold electrode, and its electrocatalysis to phenylephrine

Fluphenazine, an important tranquilizer, was found to undergo effective accumulation on dodecanethiol (DDT) self-assembled monolayer modified gold electrode (i.e. DDT/Au) and generated two anodic peaks at about 0.7 and 0.79 V (vs. SCE) in 0.05 M Na2B4O7 (pH = 9.3) buffer solution. Sensitive and quantitative measurement of fluphenazine based on the former anodic peak was established under optimum conditions. The peak current was linear to fluphenazine concentration in the range from 5 × 10−7 to 5 × 10−5 M, with a detection limit of 5 × 10−9 M. This method was successfully applied to the determination of fluphenazine in drug tablets and proved to be reliable compared with UV spectrophotometry. In the presence of fluphenazine, the electrochemical oxidation of phenylephrine was catalyzed. The DDT self-assembled monolayer was characterized by Fourier transform infrared spectroscopy, surface Raman spectroscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and electrochemical probing.

Molecular Recognition of Protonated Polyamines at Calix[4]Crown-5 Self-Assembled Monolayer Modified Electrodes by Impedance Measurements

Molecular recognition of protonated aliphatic polyamines has been studied at calix[4]crown-5 self-assembled monolayer modified gold electrodes by electrochemical impedance spectroscopic (EIS) experiments. The energy of complex formation between the calix [4]crown-5 molecule and a series of alkyl ammonium ions was shown by molecular modeling and EIS experiments to depend on the number of amine groups in the alkyl chain as well as the number of methylene groups between the amine groups. The structures of complexes formed between the crown ether on the lower rim of calix[4]arene and protonated amines were determined by minimizing the complex formation energies. The adducts thus formed on the SAM rendered the electron transfer from the electrode to the probe (Fe(CN)63-/4- pair) easier or more difficult depending on the number of ammonium groups and their arrangement in linear alkyl chains. Analytical procedures have been developed to detect protonated spermidine (a recognized cancer marker) in simulated urine, blood, erythrocyte, and cerebrospinal fluids.

Self-assembling Process of Alkanethiol Monolayers on Gold Surface via Underpotential Deposition

It was demonstrated feasible that underpotential deposition (UPD) of copper on a monolayer-modified gold substrate can be used to determine the gold electrode area. The deposition and stripping of a Cu adlayer can take place reversibly and stably at a bared or a self-assembled monolayer modified gold electrode. The growth kinetics of decanethiol/Au was also investigated via Cu UPD. The difference between the assembling kinetics determined by UPD and that by quartz crystal microbalance measurements reveals the configuration transmutation of the assembled molecules from a disordered arrangement to an ordered arrangement during the self-assembling processes.

Selective determination of uric acid in the presence of ascorbic acid using a penicillamine self-assembled gold electrode

The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode (Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry (CV). The diffusion coefficient D of UA is 6.97 × 10−6 cm2 s−1. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit was 1 × 10−6 mol L−1. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties.

Electrochemical Behavior of Dopamine at a Penicillamine Self‐Assembled Gold Electrode and its Analytical Application

The fabrication and electrochemical characteristics of penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows an obvious electrocatalytic activity for the oxidation of dopamine (DA). In phosphate buffer (pH 7.0), the peak current is proportional to the concentration of DA in the range of 8.0 x 10(-6) approximately 1.0 x 10(-3) M by the cyclic voltammetry methods with the detection limits of 4.5 x 10(-7) M. The PCA self-assembled monolayer modified gold electrode can be applied to the determination of DA in practical injection samples with simplicity, rapidness, and accurate results.

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10−6 cm2 s−1. In 0.1 mol L−1 phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10−5–2.0 × 10−4 mol L−1 and 1.0 × 10−7–1.0 × 10−6 mol L−1. The detection limit is 5 × 10−8 mol L−1. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.