Gold Disk Electrode Research Articles

Effect of SAM Chain Length on Mediated Amperometric Detection of Glucose

Alkanethiol self-assembled monolayers of three different chain lengths were used to immobilize glucose oxidase onto gold disk electrodes and the effect of the length on the kinetics of the electron-transfer reaction were investigated. 6 – mercaptohexanoic acid and 9 – mercaptononanoic acid was synthesized to provide a chain length shorter then the commercially available 11 – mercaptoundecanoic acid. The surface coverage of these SAMs, the detection sensitivity, and enzyme kinetics were investigated using cyclic voltammetry. Results showed that SAM of the 6-mercaptohexanoic acid had a higher degree of surface coverage as well as more efficient enzyme kinetics than expected.

An electrochemical biosensor based on DNA tetrahedron/graphene composite film for highly sensitive detection of NADH.

Dihydronicotinamide adenine dinucleotide (NADH) is a major biomarker correlated with lethal diseases such as cancers and bacterial infection. Herein, we report a graphene-DNA tetrahedron-gold nanoparticle modified gold disk electrode for highly sensitive NADH detection. By assembling the DNA tetrahedron/graphene composite film on the gold disk electrode surface which prior harnessed electrochemical deposition of gold nanoparticles to enhance the effective surface area, the oxidation potential of NADH was substantially decreased to 0.28V (vs. Ag/AgCl) and surface fouling effects were successfully eliminated. Furthermore, the lower detection limit of NADH by the presented platform was reduced down to 1fM, with an upper limit of 10pM. Both the regeneration and selectivity of composite film-modified electrode are investigated and proved to be robust. The novel sensor developed here could serve as a highly sensitive probe for NADH detection, which would further benefit the field of NADH related disease diagnostics.

Synthesis and quantitative characterization of non-conductive colloidal particle multilayers

We have studied theoretically and experimentally layer by layer assembled multilayers of monodisperse colloidal particles. More specifically, we have determined the effect of variations in the single-layer surface coverage on the properties of the multilayers. We have mimicked the layer by layer self-assembling process at a solid-liquid interface using the extended random sequential adsorption model of hard spheres. We have simulated ten multilayers: one with a constant single-layer coverage of 0.3 and nine others with variable single-layer coverages. We have kept the mean single-layer surface coverage of the nine multilayers at 0.3. For each of the multilayers, we have determined its mean thickness, porosity, tortuosity, and equivalent thickness of stagnant solution layer. We have found that, for not too large variations in the single-layer coverage, their effect on the mean multilayer parameters is minor. We have also tested our theoretical results experimentally. We have produced five multilayers of polystyrene latex particles of the diameter 800nm on the surface of gold disk electrodes. For each of the multilayers, we have conducted measurements of the limiting diffusion current at the rotating electrodes to determine the layer’s transport parameters. We have also used an ultra micro balance to determine the mass and mean single-layer surface coverage of each multilayer. We have found a good agreement between the numerical simulations and experiments at the surface coverage below 0.45. Our experimental results have also suggested that at higher surface coverages the colloidal particle multilayers have collapsed forming heterogeneous structures. We have demonstrated the applicability of the cyclic voltammetry and rotating disk electrode techniques for the characterization of colloidal particle multilayers.

Batch-injection stripping voltammetry of zinc at a gold electrode: application for fuel bioethanol analysis

This article reports for the first time the anodic stripping voltammetric (ASV) detection of Zn at a gold disk macroelectrode for the analysis of fuel bioethanol. The accurate determination of Zn at gold macroelectrodes was only possible with the aid of batch injection analysis (BIA) associated with ASV; this statement was proved by comparison with a conventional three-electrode system. The BIA system consisted of injections of bioethanol sample plugs (up to 1mL) at 28.3μLs−1 directly onto a working (gold disc) electrode immersed in 0.04molL−1 Britton-Robinson buffer (pH 7) solution through an electronic micropipette and the Zn deposition occurs simultaneously. The highest analytical response for Zn was obtained for a deposition time of 90s, which indicated that Zn deposition also occurred from diffusion after the injection ended. The proposed method presented a low detection limit (5μgL−1), a linear range between 25 and 250μgL−1, and adequate recovery values (88–104%) for spiked samples, but no sample treatment was required. Such remarkable analytical features associated with the portability characteristics of BIA demonstrated the promising application of the proposed method for routine and on-site determination of metals in fuel bioethanol.

Electrochemical-Nucleic Acid Detection with Enhanced Specificity and Sensitivity

Development of a rapid and label-free Electrochemical Impedance Spectroscopy (EIS) biosensor for nucleic acid detection based on sensitivity and specifies was proposed to fill the technology gap between rapid and portable detection of DNA sequences. Current biosensors have inherent limitations to sensitivity and specificity due to the monovalent character of the detection method. These limitations were significantly improved upon by constructing cooperative probes, called Tentacle Probes™ (TP), which utilize divalent binding to achieve both high sensitivity as well as extremely high specificity. Immobilization of Tentacle Probe onto gold disk electrode produced statistical significance, with p<3.0*10-13. Tentacle Probe with EIS detection was able to detect a difference between the B. AnthracisgyrA gene and B. Cereus gyrA Single Nucleotide Polymorphism sequence at a lower limit of detection of 20nM. Furthermore, B. Cereus gyrA is a common soil bacterium that causes false positives for B. AnthracisgyrA. This method of detection is current a model system for DNA detection; other genes could be detected with this system. With the potential to be transformative by providing a platform technology for both DNA and protein detection with high sensitivity this system offers extremely low rates of false positives. There is a high capacity for the technology to be multiplexed for high-throughput applications or quick diagnostic tests for medical purposes. Thus, the biomarker development will also have the potential to be assessed through noninvasive methods.

Electrochemical Detection of Chromium(VI): Induced DNA Damage

The DNA damage induced by chromium(VI) was examined with the use of gold disk electrodes modified with double-stranded DNA. DNA immobilization method and the pH conditions were optimized. The developed assay relies on the change of the reduction current of an external redox indicator - methylene blue (MB) before and after incubation in potassium chromate solution. The degrading effect of Cr(VI) on dsDNA layer was also observed with the use of quartz crystal microbalance (QCM) measurements. It was shown that the presence of ascorbic acid limits the degrading properties of chromium(VI), and further addition of H2O2 screens the antioxidant activity of ascorbic acid. In the proposed system, the MB current difference rises proportionally within the range of 1 to 100 μmol L−1 of K2CrO4, while for higher concentrations the DNA layer saturation with Cr(VI) is observed.

Voltammetric characterization of Hg2+ ion behaviour in acid media on different electrodes

Abstract This article presents some aspects related to the cathodic discharge of the mercuric ion provided from HgCl2 into an aqueous solution of 0.1 M H2SO4 on different types of electrodes: gold disc electrode (GDE), carbon paste electrode (CPE) and platinum-disk electrode (PDE). Using the rotating disk electrode technique applied on PDE it was established that the cathodic discharge mechanism for the mercuric ion is based on both process types: mass transport, achieved by diffusion and charge transfer, achieved by electron transfer from cathode to mercury ion

Electroencephalographic recordings of physiological activity of the sheep cerebral cortex.

This paper presents the physiological activity of the cerebral cortex in sheep in electroencephalo- graphic findings. The study was performed to evaluate and improve understanding of brain monitor- ing methods in freely moving animals without the use of any anaesthetic methods during the acquisi- tion stage. The aim of the study was to determine the physiological activity of the cerebral cortex in animals in a sheep model (using clinically healthy Polish Merino rams, aged 1 yr.) to determine its clinical EEG protocol. The EEG was registered using an in-lab EEG device as well as ambulatory systems (Holter EEG). The bioelectrical activity of the sheep cerebral cortex was recorded using gold disc and needle electrodes placed on experimentally determined locations on the scalp. The main finding of this study was the rhythmic EEG activity of the sheep brain in wakeful and conscious states (eyes open). The rhythm was bilaterally synchronous and determined a basic pattern in the registra- tion of physiological activity of the cerebral cortex. The acquired rhythm may correspond to the theta rhythm in humans, which is a normal activity controlled by the hippocampus. This background activity comprised intermittent episodic slow waves and synchronous beta waves.

Development of a very sensitive electrochemical immunosensor for the determination of 17β-estradiol in bovine serum samples

This study describes the development of a very sensitive electrochemical immunosensor (EI) for the determination of 17β-estradiol (17β-E). The novelty of this immunosensor is that the detection of 17β-E is carried out without sample pretreatment and unlabeled neither the antigen nor the antibody. Very good results in terms of sensitivity, kinetics, and working range are obtained. The immunosensor was constructed by immobilization of the anti-17β-E monoclonal antibody (mAbE) on a gold disk electrode modified with gold nanoparticles on a cysteamine self-assembled monolayer (AuNP-cys-Au disk). Bovine serum samples were spiked with known amounts of 17β-E and incubated on mAbE-AuNP-cys-Au disk electrodes. Then, the EI was transferred to pH 5.00 citrate buffer solutions, containing horseradish peroxidase (HRP), pyrocatechol (H2Q), and H2O2 at given concentrations. The 17β-E and H2Q, both enzyme co-substrates, react with HRP. The HRP, which did not react with 17β-E, in the presence of H2O2 catalyzes the oxidation of H2Q to o-benzoquinone (Q). The back electrochemical reduction of Q to H2Q was detected on the modified gold electrode surface by square wave voltammetry. The electrochemical signal was proportional to the amount of H2Q that reacts with the enzyme, and inversely proportional to the amount of 17β-E presents in the bovine serum samples. The EI showed a linear range from 0.54 to 1.36×104pgmL−1. The limit of detection (LOD) was 0.84pgmL−1. Recovery percentages were very good, with values of 99.7, 106, and 105% for 10, 50 and 100pgmL−1, respectively. This EI is an attractive tool for the 17β-E determination in bovine serum samples.

Development of electrochemical methods to enzymatically detect traumatic brain injury biomarkers.

As awareness of traumatic brain injury (TBI) increases, the need to detect mild forms and distinguish between the different severities of TBI becomes more apparent. The goal of this work is to develop a point-of-care sensor to detect whole blood biomarkers for rapid and sensitive diagnosis of TBI severity. Presented herein is the enzymatic detection of norepinephrine through the use of immobilization chemistry and impedance techniques. Sustained elevation of norepinephrine concentrations in the blood has been correlated to negative long-term outcomes in TBI cases, often resulting in permanent cognitive or physical deficits. Novel analysis techniques have been used to identify an optimal binding frequency (371.1 Hz) of norepinephrine to the immobilized enzyme on a gold disk electrode. This form of analysis yielded a logarithmic fit characterized by exceptional responsivity (20.89 Ω/pg mL(-1)), reproducibility (R(2)=0.96), and lower limit of detection (98 pg/mL) first in purified samples, then in rabbit whole blood solutions. Once the optimal binding frequency was determined, the preliminary use of an impedance-time technique was attempted in this work. This technique more closely resembles the amperometric detection method used in commercial self-monitoring blood glucose meters, allowing for continuous or instantaneous measurement of blood borne biomarkers without compromising sensitivity. Future directions include exploration of simultaneous multi-marker detection with the impedance-time technique and experimentation with novel mesoporous materials to filter large blood components.

Electrochemical impedance spectroscopy study of proteolysis using unmodified gold nanoparticles

Proteases are involved in numerous cell functions and abnormal proteolysis may lead to a diversity of serious diseases. Herein, a simple electrochemical method is developed to study proteolysis by employing unmodified gold nanoparticles (AuNPs). Substrate of a protease is modified on a gold disk electrode, forming a barrier for electrochemical species and reflecting a significant charge transfer resistance (Rct). After the proteolysis process, the substrate can be cleaved coupled with the decline of Rct. The electrical properties of the substrate residues on the electrode may also change, leading to the subsequent adsorption of AuNPs. Due to the excellent electrical conductivity of AuNPs, Rct can be further decreased, which can be used to reveal the proteolysis process. The proposed method allows the determination of the model protease, trypsin, with desirable sensitivity and specificity. It may also hold great potential use in the study of other proteolysis processes and some biomedical applications in the future.

Voltammetric Determination of TBHQ Individually and Mixed with BHT in Petroleum Products Using a Gold Disc Electrode

A new method is proposed for determination of TBHQ (tert-butylhydroquinone) individually and in a mixture with BHT (butylated hydroxytoluene) in mineral oil and biodiesel when using linear-sweep voltammetry in combination with a gold disc electrode. Both of these analytes gave rise to the respective anodic peak in the supporting electrolyte based on a mixture of dilute H2SO4 and isopropanol. The samples of mineral oil were extracted using ethanol, and the samples of biodiesel were analyzed without any special sample treatment or separation. The electroanalytical method developed has enabled the determination of antioxidants in model and real samples with satisfactory results and good prospects for practical analysis.

4-Fluoro-3-nitrophenyl grafted gold electrode based platform for label free electrochemical detection of interleukin-2 protein

A new platform based on 4-Fluoro-3-nitrophenyl (FNP) grafted gold disk electrode prepared via electrochemical reduction of 4-fluoro-3-nitrobenzene diazonium ion has been developed and utilized for biosensor fabrication. Anti-interleukin-2 (anti-IL2) antibody has been covalently immobilized onto FNP/Au surface and utilized for label free electrochemical impedance based detection of cytokine IL2. FNP acts as a bridge (cross-linker) between gold surface and anti-IL2, where fluoro group of FNP undergoes nucleophilic substitution by amino group of biomolecule and results in its covalent immobilization. The immobilization process and fabricated electrode have been characterized using contact angle (CA) measurements, cyclic voltammetry (CV) and electrochemical impedance (EIS) technique. CV studies show that FNP grafted surface provides conductive surface for anti-IL2 immobilization. The EIS response of studies as a function of IL2 concentrations exhibits a detection in linear range from 1pgml−1 to 10ngml−1 with minimum detectable concentration of 1pgml−1. The electrode has been found to be selective against other cytokine molecules.

Characterization of cysteamine self assembled on gold functionalized with nitrilotriacetic acid and evaluation of copper(II) binding capacity with adsorption transfer stripping voltammetry

A self assembled monolayer of cysteamine was prepared on the surface of gold disc electrode and further modified with nitrilotriacetic acid. Modified electrode was characterized with cyclic voltammetry and electrochemical impedance spectroscopy in presence of potassium hexacyanoferrate(II)/(III). Thus prepared electrode was tested for determination of Cu2+ with adsorption transfer stripping voltammetry. The binding of Cu2+ onto the modified electrode was successfully performed for a wide range of tested concentrations. Electrode response (logIp) was linearly proportional to −logc(Cu2+) with correlation coefficient R2=0.9759. The detection limit was 1·10-8M. The influence of interfering substances (Mg2+, Mn2+, Co2+, Ni2+ and Pb2+) was tested and it was found that Mg2+ and Pb2+ do not interfere while Mn2+, Co2+ and Ni2+ show slight interference. Real-world testing of copper content in urine samples confirmed practical application of prepared sensor.

Simultaneous determination of BHT and BHA in mineral and synthetic oils using linear scan voltammetry with a gold disc electrode

A new method has been proposed for the simultaneous determination of BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) in mineral and synthetic oils when using linear-sweep voltammetry in combination with a gold disc electrode. Both analytes of interest gave rise to the respective anodic peak in the supporting electrolyte based on a mixture of diluted H2SO4 and isopropanol. Partial overlaps of both signals could be resolved by special mathematical treatment of the corresponding voltammograms with the aid of simple procedure proposed by the authors. Then, electroanalytical method developed has enabled the determination of both BHA and BHT in model mixtures with satisfactory results and prospects for practical analysis.

Dual function metal nanoparticles: Electrocatalysis and DNA capture

Dual function platinum nanoparticles (PtNPs) incorporating two functions, i.e., DNA capture and electrocatalysis that are physically separated, are described. The physical separation of the two functions significantly enhances the sensitivity of DNA detection giving attomolar limits of detection. The regio-selective functionalisation has been achieved using defects within a dodecanethiol (C12) monolayer deposited on a gold electrode. These defects–nucleation sites allow for the electrodeposition of electrocatalytic, mushroom shaped PtNPs. The monolayer allows one side of the nanoparticle to be functionalised with a 20-base oligonucleotide with a C3 spacer thiol (probe) that selectively captures a sequence specifically associated with the strain of Staphylococcus aureus associated with mastitis. Once functionalised with capture strand DNA, the particles are released by sonication which maintains the structural integrity of the DNA. Thus, the desorbed nanoparticles are capable of biorecognition on the top curved side and electrocatalytic reduction of hydrogen peroxide on the non-functionalised lower surface. A second gold disc electrode was modified with a 15-base oligonucleotide with a C3 spacer thiol (capture). The presence of a 41-base target oligonucleotide, S. Aureus, which hybridized with both capture and probe oligonucleotides, brings the PtNP close to the electrode surface facilitating the electrocatalytic reduction of hydrogen peroxide generating a significant current for each hybridisation event. This highly sensitive detection approach opens up the possibility of avoiding polymerase chain reaction (PCR) or nucleic acid sequence-based amplification (NASBA) based amplification of the target.

Significant contribution of three-phase boundary for the oxygen reduction current in DMSO solution at a gold disk electrode in hanging meniscus configuration

Significant contribution of three-phase boundary for oxygen reduction reaction at a gold disk electrode in hanging meniscus configuration in dimethyl sulfoxide (DMSO) solution was demonstrated. While cyclic voltammograms (CVs) with symmetrical shape representing quasi-reversible kinetics were obtained for oxygen reduction reaction (ORR) at a Au disk electrode in an ordinary configuration when it was fully immersed in an O2 saturated 0.1M tetrabutylammonium hexafluorophosphate (TBAPF6) DMSO solution, asymmetric CVs with enhanced ORR current were obtained at a Au disk electrode in the hanging meniscus configuration. Origin of this feature was investigated at a gold wire electrode, which was immersed partly in the solution, in detail by changing the concentrations of O2 in the gas phase and in solution independently as well as the immersion depth. All the results confirm that the ORR at the three-phase, O2 gas/Au electrode/electrolyte solution, boundary contributes dominantly to the observed current in the hanging meniscus configuration.

Vapour phase polymerised polyaniline–gold nanoparticle composites for DNA detection

Polyaniline, PANI, films have been deposited on gold disc electrodes by vapour deposition using an Fe (III) tosylate oxidant. Gold nanoparticles were then electrodeposited to give a nanocomposite material, PANI–AuNP. UV–visible and Raman spectroscopy indicate that film contains PANI in both the base and salt states. Thiolated capture strand DNA, that is complementary to a section of the sequence from the pathogen Staphylococcus aureus that causes mammary gland inflammation, was then immobilized onto the gold nanoparticles and any exposed underlying gold electrode. Following hybridisation of the target, a probe strand, labelled with horse radish peroxidase was hybridized to the section of the target not bound to the capture strand. The concentration of the target was determined by measuring the current required to reduce benzoquinone generated by the HRP label. Semi-log plots of the pathogen DNA concentration vs. faradaic current are linear from 150pM to 1μM and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification.

Highly selective detection of dopamine in the presence of ascorbic acid and uric acid using thioglycolic acid capped CdTe quantum dots modified electrode

In this work, cadmium telluride (CdTe) quantum dots (QDs) have been successfully applied for construction of a novel chemically modified electrode for determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). The small CdTe QDs were synthesized by using a wet chemical routes in the presence of thioglycolic acid (TGA), as capping agent at pH 9.5, having particle diameters of 1–3nm. The synthesized QDs were immobilized on the surface of gold disk electrode by self assembly method in dark conditions for 30h and electrochemically characterized. The modified CdTe QDs-based electrode afforded the simultaneous detection of these three compounds with wide peak separations, which allowed the interferences to be masked with applied potential. Using a potential window of 0–350mV, where only dopamine was electroactive, a detection limit of 8.27×10−9M and 1.30×10−9M were calculated from square wave voltammetry and amperometry, respectively.

Oxygen biosensor based on bilirubin oxidase immobilized on a nanostructured gold electrode

Gold disk electrodes modified with gold nanoparticles have been used as a scaffold for the covalent immobilization of bilirubin oxidase. The nanostructured bioelectrodes were tested as mediator-less biosensors for oxygen in a buffer that mimics the content and the composition of human physiological fluids. Chronoamperometry measurements showed a detection limit towards oxygen of 6±1μM with a linear range of 6-300μM, i.e. exceeding usual physiological ranges of oxygen in human tissues and fluids. The biosensor presented is the first ever-reported oxygen amperometric biosensor based on direct electron transfer of bilirubin oxidase.